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Combat food fraud: Meet Misa

Combat food fraud: Meet Misa

What’s on your plate?

Food fraud is an ever-present danger around the world. Despite increased regulations, huge scandals still occur regularly, such as deliberately tainted infant formula (2008), or the horse meat affair in the UK due to improper labelling (2013). Other more common examples include the adulteration of highly valued items with lower cost substitutes, or the illegal enhancement of color in foods and beverages with unsafe dyes.

As the population continues to increase, driving the demand for high quality food and beverage choices, so will the amount of food fraud cases. Only a concerted effort to test foodstuffs more frequently in an efficient manner along the supply chain with accurate and precise analytical techniques will bring these cases to light before more people come to harm.

Misa to the rescue

Meet the newest addition to the Metrohm Instant Raman Analyzer family: Misa, the Metrohm Instant SERS Analyzer. Misa is fast, smart, and portable with powerful algorithms that simplify high-tech analyses for non-technicians. Misa is designed with safety in mind, purposefully designed to detect illicit drugs and food additives in complex matrices.

The SERS Principle

Surface Enhanced Raman Scattering (SERS) is an extension of Raman. Perhaps you read in my previous blog post about Raman spectroscopy that «If you can see it, Raman can ID it»… well, SERS amplifies the Raman signal of trace analytes, making it an extremely sensitive method for «ID when you can’t see it.»

When SERS-active analytes adsorb to silver or gold nanoparticles, their Raman signal is enhanced as much as a million-fold, providing incredibly sensitive detection abilities.

SERS is used in biosensor applications, including single-cell sensing, antibody detection, and pathogen monitoring. It can be used to detect chemical warfare agents and illicit drug laboratory residues. Additionally, SERS is a particularly powerful technique for detecting trace contaminants in foodstuffs such as antibiotics fungicides, pesticides, herbicides, illicit dyes, and other additives.

If you know ID Kit for Mira DS, then you already know a little about SERS. SERS is an «enhancement» technique to Raman that enables detection of trace materials. For example, ID Kit was developed as a method for identifying heroin and fentanyl in street drug samples. The cutting agents and added stimulants that constitute the bulk of street heroin fluoresce under investigation with Raman and overwhelm the signal coming from heroin. SERS sees right through the cutting agents and identifies the drug.

Overlaid Raman and SERS spectra demonstrating the ability of SERS to detect the active ingredient in street heroin.

Another example of how Raman and SERS complement each other can be seen with Yaba, a common street drug in southeast Asia. Yaba is a red tablet that contains significant caffeine with a small amount of methamphetamine. When a red Yaba tablet is analyzed with Raman, caffeine and the red dye in the coating are the primary identification targets. This makes sense, because Raman is very good at identifying bulk materials.

However, when a Yaba tablet is subjected to SERS analysis, the story is very different (reminder: these are both also capabilities of Mira DS!) Only SERS can ID the methamphetamine in Yaba and complete the story.

Protecting Consumer Safety with Misa

Consumer safety relies on the ability of food inspectors to detect unwanted additives and assure the quality of the products. Trace detection of food adulterants is traditionally very involved laboratory work, using HPLC, GC/MS, and other techniques requiring extensive sample preparation and scientific training. Misa is designed to simplify food testing, from sample preparation, to sharing results.

The unique capabilities of Misa and SERS analysis in food testing deserve some explanation. Raman is used in food testing in some incredible ways: identifying counterfeit honey, distinguishing scotch from different producers, discriminating between very similar sugars, even making a distinction between grass- and grain-fed beef. However, these are bulk, inherent qualities of a food.

Looking for trace levels of pesticides is a very different science. A successful SERS analyte must interact with nanoparticles—target molecules with amine, carboxyl, and thiol groups often have the required interaction. Fortunately, many food additives fit this definition. Metrohm Raman sponsored a year-long study to identify 82 different food adulterants that can be successfully detected with our SERS substrates. That was just the beginning.

Are you looking for applications suitable for Misa? Check out our free selection of application notes available on the Metrohm website: 

Additionally, reference spectra for several other analytes can be obtained by contacting your local Metrohm  sales organization. 

The next step was to determine the foods which were typically treated with these illicit substances, then how to simplify sample preparation for potentially demanding food matrices. Metrohm Raman is taking two different approaches to this challenge. First, Misa will be released with 17 different «real world» food safety applications (click to download):

Misa is a unique instrument, which is reflected in this broad collection of Application Notes (AN). In addition to standard spectra and experiments, each AN includes a special section titled «Field Test Protocol». Briefly, the Field Test Protocol guides any user through a complete experiment using Misa and the tools in the ID Kits. ID Kits for Misa contain dedicated SERS substrates, in addition to the basic tools required for field testing. These, combined with companion Operating Procedures included on Misa, make food safety testing accessible to anyone, anywhere.

Our second approach to application development for Misa is a very interactive process with our users as we identify the target and food matrix, provide standard spectra for library building, advise sample preparation, and help to optimize results. This approach acknowledges that food is different around the world, adulterants vary, and concerns may be localized. These ANs that accompany Misa at release are intended to give the user an idea of how to use SERS and when it is a useful technique for detection of food contaminants, but custom applications will certainly increase demand for Misa.

Metrohm Raman is excited to introduce you to Misa. Misa has all of the qualities that you appreciate about Mira—intuitive user interface, simple guided workflow, and smart attachments to facilitate onsite testing by non-chemists. Our approach to simplifying food testing includes libraries, dozens of reference spectra, and developed applications targeting food adulterants.

Visit our website

and discover more about how Misa can help the fight against food adulteration scandals.

Post written by Dr. Melissa Gelwicks, Technical Writer at Metrohm Raman, Laramie, Wyoming (USA).

Trace metal analysis with solid-state electrodes – Part 1

Trace metal analysis with solid-state electrodes – Part 1

This new series of blog posts covers a range of new sensors suitable for the determination of «heavy metals» using voltammetric methods.

The quantification of heavy metal ions plays an important role in many applications, including environmental monitoring, waste management, research studies, or even in clinical tests. Heavy metals occur naturally, but the rise of industrialization and urbanization in the past two centuries are responsible for increased levels in our environment. These dangerous elements are released and accumulate in the soil, and in ground or surface water. They enter the food chain directly from drinking water or through bioaccumulation in plants and animals. It is for this reason that pregnant women are discouraged from eating seafood, on the basis of mercury (Hg) accumulation through the food chain.

The degree of toxicity depends on the type of metal, its biological role, and most importantly, its concentration. Increased concentrations of lead, iron, cadmium, copper, arsenic, chromium, or nickel in drinking water are most often responsible for human poisoning. To highlight the toxicity of certain heavy metals in drinking water and to protect human health, guideline values or limit values for the heavy metal concentration in drinking water have been set by international organizations as the World Health Organization (WHO) or by such authorities as the U.S. Environmental Protection Agency (EPA) or the European Commission.

Several techniques have been developed for heavy metal ion analysis in the past. Commonly used techniques include atomic absorption spectrometry (AAS), inductively coupled plasma (ICP), or fluorescence spectrometry. However, these techniques require expensive equipment combined with high maintenance costs and trained personnel. Therefore, a price-effective, straightforward and sensitive method that allows detection of metal ions in water samples is highly desired.

Stripping voltammetry is the right solution for these challenges providing a simple, rapid, and cost-effective alternative for the aforementioned techniques that is also suited for untrained personnel. In addition, detection limits in the ng/L range and the possibility to determine the trace levels of heavy metals in the field make it so interesting and valuable.

The principle of stripping voltammetry

Voltammetric determination of heavy metals consists of two steps. In the first step, the analyte is preconcentrated on the surface of the working electrode as shown using the example of anodic stripping voltammetric determination of lead (Pb) in Figure 1.

Figure 1. Anodic stripping voltammetry – deposition of lead (solution stirred).

In the subsequent stripping step (Figure 2), the analyte is released. This can be achieved by oxidation or reduction depending on the method used for the determination. This step generates the analytical signal, which has to be proportional to the deposited amount of analyte.

Figure 2. Anodic stripping voltammetry – stripping of lead (solution not stirred).

Besides anodic stripping voltammetry, cathodic stripping voltammetry or adsorptive stripping voltammetry are also possible to utilize and work in a similar manner. All of these methods have something in common: every voltammetric determination is as good as the sensor used for the measurement. Therefore, in this series of posts we want to introduce our powerful sensors and demonstrate the outstanding performance with a few typical applications.

Need for new sensors

The need for heavy metal ion determinations in the field, sensor costs, and environmental issues are the main triggers for research on new sensors in voltammetry. Non-toxic and inexpensive materials are preferred for new sensors. The properties of these materials, however, can lead to some restrictions. First is the limited number of elements that can be detected on a particular electrode material (e.g., gold, carbon or bismuth). In addition, it is difficult to determine several elements simultaneously at the same mercury-free sensor. The choice of the most suitable electrode material in combination with the optimum sensor design helps to overcome these issues.

Bismuth as an alternative electrode material

In the past, there were many attempts to find less toxic electrode materials than mercury for the determination of heavy metal ions, but none have achieved exceptional electroanalytical performance. Twenty years ago (2000), an American researcher by the name of Joseph Wang reported a bismuth film electrode for the first time (Joseph Wang, 2000).

Figure 3. Bismuth crystal.

After this initial revolutionary report, bismuth-based electrodes prepared as in-situ and ex-situ films on solid-state electrodes such as carbon, have been growing in popularity. The broad electrochemical window and low toxicity of bismuth were key factors. In addition, bismuth is able to form alloys with quite a high number of heavy metals and it exhibits high hydrogen overpotential, similar to mercury. These properties are particularly interesting for stripping voltammetry. The hydrogen evolution is suppressed very efficiently with the consequence that noise-free measurements at negative potentials can be carried out. Bismuth electrodes based on bismuth films are a good option. However, film deposition is an additional step that is time-consuming.

New sensor in VA: the Bi drop electrode

With the Bi drop electrode, a novel solid-state electrode is now available for the determination of heavy metal ions in drinking water. A bismuth drop of approximately 2 mm diameter serves as the working electrode within the voltammetric measurement.

The electrode works without the need for polishing or film deposition—only electrochemical activation is required. This significantly shortens the entire analysis time. Once activated, series of heavy metal determinations with high repeatability in the low μg/L and even ng/L range are possible.

The Bi drop electrode allows for mercury-free monitoring of the limit values of the heavy metals cadmium, lead, nickel, cobalt, and iron in drinking water. Since the electrode does not require mechanical treatment, it is especially suitable for online applications. Another advantage of the Bi drop electrode is fact that cadmium and lead as well as nickel and cobalt can be determined simultaneously.

The sensor is cost-efficient, stable, extremely sensitive, and is able to deliver more reproducible results than other previously examined bismuth-based electrodes. To demonstrate the broad possibilities and flexibility of the Bi drop electrode, examples for anodic stripping voltammetry, adsorptive stripping voltammetry, and direct voltammetric determination will be presented and discussed.

Applications

Anodic stripping voltammetric determination of cadmium and lead

To reduce the toxic effects of cadmium on the kidneys, skeleton, and respiratory system, as well as the neurotoxic effects of lead, the provisional guideline values in the World Health Organization’s «Guidelines for Drinking-water Quality» are set to a maximum concentration of 3 µg/L for cadmium and 10 µg/L for lead.

Figure 5. Example for determination of cadmium and lead in tap water spiked with β(Cd) = 2 µg/L and β(Pb) = 2 µg/L.

A completely mercury‑free sensor, the Bi drop electrode allows the simultaneous determination of cadmium and lead in drinking water without any additional film plating step. With a 60 s deposition time, a limit of detection (LOD) of 0.1 µg/L for cadmium and 0.5 µg/L for lead can be achieved. This outstanding sensitivity is more than sufficient to monitor the provisional WHO guideline values.

Not only is the sensitivity impressive, but also the reproducibility and accuracy. The relative standard deviation for 10 measurements in a check standard solution (β(Cd) = 1 µg/L and β(Pb) = 5 µg/L) is 5% and 3%, and the recovery rate is 90% and 100% for cadmium and lead, respectively.

Direct determination of iron

The presence of iron in drinking water can lead to an unpleasant, harsh metallic taste or reddish-brown stains. In addition, «iron bacteria» which can grow in waters containing iron as low as 100 µg/L, create a reddish-brown slime that can clog plumbing and cause an offensive odor. Over a longer period, the formation of insoluble iron deposits is problematic in many industrial and agricultural applications, such as water supply, system cooling, or field irrigation. To avoid these problems, the U.S. Environmental Protection Agency (EPA) defines the Secondary Maximum Contaminant Level (SMCL) for water treatment and processing plants as 300 µg/L iron in drinking water.

Figure 6. Example for determination of iron in tap water spiked with β(Fe) = 20 µg/L.

The voltammetric determination of the iron triethanolamine complex on the non-toxic Bi drop electrode does not require enrichment. The system uses catalytic signal enhancement, allowing both the detection at very low levels with a limit of detection of 5 µg/L and measurements in a wide range of concentrations up to 500 µg/L.

This method is best suited for automated systems or process analyzers, allowing fully automatic determination of iron in a large sample series and providing stable results. The relative standard deviation for 10 measurements in a check standard solution (β(Fe) = 50 µg/L) is 3% and the recovery rate is 111%.

Adsorptive stripping voltammetric determination of nickel and cobalt

The main sources of nickel pollution are from electroplating processes, metallurgical operations, or leaching from pipes and fittings. Catalysts used in the petroleum and chemical industries are major application fields for cobalt. In both cases, the metal is either released directly, or via the wastewater–river pathway into the drinking water system. Therefore in the EU, the legislation specifies 20 µg/L as the limit value for the nickel concentration in drinking water.

The simultaneous and straightforward determination of nickel and cobalt is based on adsorptive stripping voltammetry (AdSV). The unique properties of the non-toxic Bi drop electrode combined with AdSV results in an excellent performance in terms of sensitivity. The limit of detection for 30 s deposition time is approximately 0.2 µg/L for nickel and 0.1 µg/L for cobalt, and can be lowered further by increasing the deposition time.

Figure 7. Determination of nickel and cobalt in tap water spiked with β(Ni) = 0.5 µg/L and β(Co) = 0.5 µg/L.

This method is best suited for automated systems or process analyzers, allowing fully automatic determination of these metals in large sample series and providing stable and accurate results. The relative standard deviation for 10 subsequent measurements in a check standard solution (β(Ni) = 1 µg/L β(Co) = 1 µg/L) is 4% and 5% and the recovery rate is 106% for nickel and 88% for cobalt.

Key features of the Bi drop electrode

  • Non-toxic, completely mercury-free alternative for trace metal determination
  • Simultaneous determination of Ni and Co, as well as Cd and Pb
  • Limit of detection in low μg/L and even ng/L range
  • Suitable for automated and online systems

What’s next?

In the next installment, we will take a look at a cost-efficient and semi-disposable sensor for heavy metal detection: the scTRACE Gold and its associated applications.

Post written by Dr. Jakub TymoczkoApplication Specialist VA/CVS at Metrohm International Headquarters, Herisau, Switzerland.

Comprehensive water analysis: combining titration, IC, and direct measurement in one setup

Comprehensive water analysis: combining titration, IC, and direct measurement in one setup

If you perform water analyses on a regular basis, then you know that analyzing different parameters for drinking water can be quite time-consuming, expensive, and it requires significant manual labor. In this article, I’d like to show you an example of wider possibilities in automated sample analysis when it comes to combining different analytical techniques, especially for our drinking water.

Water is the source and basis of all life. It is essential for metabolism and is our most important foodstuff.

As a solvent and transporting agent it carries not only the vital minerals and nutrients, but also, increasingly, harmful pollutants, which accumulate in aquatic or terrestrial organisms.

Within the context of quality control and risk assessment, there is a need in the water laboratory for cost-effective and fast instruments and methods that can deal with the ever more complex spectrum of harmful substances, the increasing throughput of samples, and the decreasing detection limits.

Comprehensive analysis of ionic components in liquid samples such as water involves four analytical techniques:

  • Direct measurement
  • Titration
  • Ion chromatography
  • Voltammetry

Each of these techniques has its own particular strengths. However, applying them one after the other on discrete systems in the laboratory is a rather complex task that takes up significant time.

Back in 1998, Metrohm accepted the challenge of combining different analytical techniques in a single fully automated system, and the first TitrIC system was introduced.

What is TitrIC?

The TitrIC system from Metrohm combines direct measurement, titration, and ion chromatography in a fully automated system.

Direct measurements include temperature, conductivity, and pH. The acid capacity (m and p values) is determined titrimetrically. Major anions and cations are quantified by ion chromatography. Calcium and magnesium, which are used to calculate total hardness, can be determined by titration or ion chromatography.

The results are displayed in a common table, and a shared report is given out at the end of the analysis. All methods in TitrIC utilize the same liquid handling units and a common sample changer.

For more detailed information about the newest TitrIC system, which is available in two predefined packages (TitrIC flex I and TitrIC flex II), take a look at our informative brochure:

Efficient: Titrations and ion chromatography are performed simultaneously with the TitrIC flex system.

Figure 1. Flowchart of TitrIC flex II automated analysis and data acquisition.

How does TitrIC work?

Each water sample analysis is performed fully automated at the push of a button—fill up a sample beaker with the sample, place it on the sample rack, and start the measurement. The liquid handling units transfer the required sample volume (per measurement technique) for reproducible results. TitrIC carries out all the work, and analyzes up to 175 samples in a row without any manual intervention required, no matter what time the measurement series has begun. The high degree of automation reduces costs and increases both productivity and the precision of the analysis.

Figure 2. The Metrohm TitrIC flex II system with OMNIS Sample Robot S and Dis-Cover functionality.

To learn more about how to perform comprehensive water analysis with TitrIC flex II, download our free application note AN-S-387:

Would you like to know more about why automation should be preferred over manual titration? Check out our previous blog post on this topic:

Calculations with TitrIC

With the TitrIC system, not only are sample analyses simplified, but the result calculations are performed automatically. This saves time and most importantly, avoids sources of human error due to erroneously noting the measurement data or performing incorrect calculations.

Selection of calculations which can be automatically performed with TitrIC: 

  • Molar concentrations of all cations
  • Molar concentrations of all anions
  • Ionic balance
  • Total water hardness (Ca & Mg)
  • … and more

Ionic balances provide clarity

The calculation of the ion balance helps to determine the accuracy of your water analysis. The calculations are based on the principle of electro-neutrality, which requires that the sum in eq/L or meq/L of the positive ions (cations) must equal the sum of negative ions (anions) in solution.

TitrIC can deliver all necessary data required to calculate the ion balance out of one sample. Both anions and cations are analyzed by IC, and the carbonate concentration (indicative of the acid capacity of water) is determined by titration.

If the value for the difference in the above equation is almost zero, then this indicates that you have accurately determined the major anions and cations in your sample.

Advantages of a combined system like TitrIC

  • Utmost accuracy: all results come from the same sample beaker

  • Completely automated, leaving analysts more time for other tasks

  • One shared sample changer saves benchtop space and costs

  • Save time with parallel titration and IC analysis

  • Flexibility: use titration, direct measurement, or IC either alone or combined with the other techniques

  • Single database for all results and calculation of the ionic balance, which is only possible with such a combined system, and gives further credibility to the sample results

Even more possibility in sample analysis

TitrIC has been developed especially for automated drinking water analysis but can be adapted to suit any number of analytical requirements in food, electroplating, or pharmaceutical industries. Your application determines the parameters that are of interest.

If the combination of direct measurement, titration, and IC does not suit your needs, perhaps a combination of voltammetry and ion chromatography in a single, fully automatic system might be more fitting. Luckily, there is the VoltIC Professional from Metrohm which fulfills these requirements.

Check out our website to learn more about this system:

As you see, the possibility of combining different analysis techniques is almost endless. Metrohm, as a leading manufacturer of instruments for chemical analysis, is aware of your analytical challenges. For this reason, we offer not only the most advanced instruments, but complete solutions for very specific analytical issues. Get the best out of your daily work in the laboratory!

Discover even more

about combined analytical systems from Metrohm

Post written by Jennifer Lüber, Jr. Product Specialist Titration/TitrIC at Metrohm International Headquarters, Herisau, Switzerland.

Virus detection using screen-printed electrodes

Virus detection using screen-printed electrodes

With significant global viral outbreaks becoming the norm rather than generational outliers, it is imperative that fast, sensitive, and cost-effective testing is available to the masses. It is only by a concerted effort of testing and tracing that viral outbreaks can be effectively controlled before becoming global pandemics.

Screen-printed electrodes (SPEs) allow rapid, widespread testing of populations for infectious disease, without the need of skilled personnel or burdensome equipment in the field. The possibility of point-of-care (POC) testing with SPEs has been exhibited in several recent studies. Metrohm DropSens, as a manufacturer of SPEs as well as their compact measuring devices, is the right partner for virology research projects—big and small. With a high production capability, combined with a valid ISO 13485 certification «Manufacturing of sensors for medical devices», this means testing procedures developed on DropSens SPEs can be reliably scaled up for larger operations, with easier approval by the Food and Drug Administration (FDA). As the leading brand in the market for this printing technology, Metrohm DropSens can design custom-made SPEs and offers the expertise and exceptional customer support needed for complicated projects at scale.

Viral outbreaks and human health

Unlike the majority of bacteria, most viruses cause disease. Viruses, however, cannot survive without hosts, and therefore spread easily especially in densely populated areas. While bacterial infections can be fought with a range of antibiotics, viruses require specific vaccines, which can be extremely difficult to manufacture.

Several viral outbreaks have caught global attention and attracted calls for faster, more accessible testing, including Ebola, avian influenza virus (H5N1, H1N1, and others), hepatitis, malaria, noroviruses, dengue, adenovirus, SARS (severe acute respiratory syndrome, HIV (human immunodeficiency virus), and even HPV (human papillomavirus). While some are capable of killing their human hosts in a relatively short timespan, others can linger for decades.

One commonality between these diseases is that they have all been successfully tested with disposable, custom-made SPEs from Metrohm DropSens.

The global pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), more commonly known as «COVID-19», has monopolized the headlines for months. Each country’s response has varied: from the tactics of encouraging normalcy to attempt quicker herd immunity, to extremely strict quarantine measures, especially for the elderly, and the closure of borders and non-essential industries. However, the most effective way to trace and contain the spread of viruses is through comprehensive testing.

General viral testing methods and their drawbacks

The importance of testing for the presence of harmful viruses in the population cannot be overstated. In order to stop the spread of especially communicable diseases, testing must be accurate, reliable, timely, affordable, and of course widely available.

Viral testing can be accomplished via several different methods, including virus isolation cultures, enzyme-linked immunosorbent assay (ELISA), and other molecular methods like polymerase chain reaction (PCR) and reverse transcription polymerase chain reaction (RT-PCR).

High costs limit the affordability and overall availability of such tests to the general population, especially for poorer communities. Complicated analytical procedures require trained professionals, specialty chemicals, and bulky instruments, which may not be available in all areas. On top of this, the waiting time between test and result is prohibitive – sometimes taking several days, which could mean the difference between life or death.

Benefits of electrochemical testing

Recently, initiatives for diagnostic testing methods have been launched by agencies such as the WHO to create faster, more accurate, affordable tests—especially in low-resource areas. For these reasons, electrochemical testing methods have been developed on disposable screen-printed electrodes, exhibiting major promise for fast, affordable, precise testing directly at the point of care.

Speed

The rapid testing capabilities of electrochemical biosensors is among one of their greatest advantages. Results are obtained within minutes, rather than hours or days with other conventional techniques. Waiting for days for results can lead to further viral communication in the community, or even death in the absence of proper care. Earlier response is vital to stopping the spread of disease and the key to saving lives.

Limit of detection

Specific electrochemical detection techniques (e.g., voltammetric or amperometric analysis) already allow for the detection of low analyte concentrations. The high adsorption capabilities of carbon-based working electrodes where certain recognition elements are attached play a key role in the improvement of sensitivity. To further decrease the detection limit, signal amplification by chemical or electrochemical catalytic reactions are commonly used.

Ease of use

The compact size of the measuring device, not to mention the SPEs themselves, equates to complete portability for testing on the go. Simply add a small volume of sample to the electrode, insert it into the measuring device, and receive results about viral exposure in minutes.

Cost

The low cost per test is a great advantage of using screen-printed electrodes for virology studies. Each SPE is meant to be disposable after a single use, ensuring a fresh substrate for every sample. The affordability and portability of SPEs and their measuring devices makes this technique much more attractive for economically depressed areas or regions without an abundance of specialized testing facilities.

Regulatory approval

Metrohm DropSens is certified by ISO 13485 «Manufacturing of sensors for medical devices». This certification permits a simpler pathway to regulatory approval (such as by the FDA) and leads to quicker commercialization of validated tests developed on these products in the medical field.

Customization

Metrohm DropSens has the technology to develop screen-printed electrodes based on the individual needs of the customer. The configuration and dimensions of the electrodes are adapted to their specific requirements.

Selection of screen-printed electrodes manufactured by Metrohm DropSens.
Availability

The large-scale manufacturing capabilities at Metrohm DropSens guarantee a trusted, reliable source for the mass production of SPEs suitable for viral testing. With decades of electrochemical expertise, a worldwide distribution network, and top class after-sales support, the widespread commercialization of tests developed on these products is no problem.

Summary

Point-of-care testing with screen-printed electrodes allows rapid, widespread testing of populations for viral outbreaks at low cost and without the need for skilled analysts or complicated measuring equipment. Fast results mean quicker reaction times – for swift treatment, but also for tracing the spread of contagion and developing a concerted response before the situation gets more out of control.

Portability and the simplicity of use allows rapid testing with screen-printed electrodes in all situations, not only off-site in specialized laboratories with a skilled staff. Since SPEs are customizable, they can be modified and manufactured to suit the needs of all types of research groups.

Metrohm DropSens SPEs, which are ISO 13485 certified, means testing procedures developed on these products require shorter times to receive FDA approval and commercialization. The bulk manufacturing capability of Metrohm DropSens guarantees a stable commercial source for custom-made SPEs and their measuring devices at any order size—big or small.

Metrohm DropSens: a complete solution provider

As a market leader in manufacturing reliable screen-printed electrodes as well as their measuring devices, Metrohm DropSens is the ideal partner for virology studies based on electrochemical testing, as well as for other research involving SPEs. For more information, Visit the Metrohm DropSens website at www.dropsens.com to have an overview of our products, capabilities, and additional peer-reviewed scientific literature featuring these electrodes and measuring devices.

For more information, visit the Metrohm DropSens website to have an overview of our products, capabilities, and additional peer-reviewed scientific literature featuring these electrodes and measuring devices.

Download our free white paper to learn more

Virus detection: Fast, sensitive, and cost-effective with electrochemical testing

Post written by Dr. Alyson Lanciki, Scientific Editor at Metrohm International Headquarters, Herisau, Switzerland.

Save money by using automated titration systems

Save money by using automated titration systems

Perhaps you read my last blog entry: «Why consider automation – even for simple titrations» and liked the idea of disengaging yourself from the tedious, repetitive, and exhausting manual routine lab work by automating analyses and increasing the accuracy and reproducibility of your results at the same time.

Titration is known to be a bargain analytical method, as a glass buret or even a simple stand-alone titrator are quite inexpensive in comparison with other techniques such as spectroscopy or chromatography. In combination with the short determination time and results based on a known stoichiometry, titration is well-accepted in laboratories worldwide as a primary method.

Nevertheless, the increasing sample throughput in the last decades shows more and more why it is worth it to automate lab analysis. On many occasions, I had discussions with lab managers or purchasing agents who had doubts about buying an automation system for the «cheap» titration technique. These concerns are understandable, especially when adding automation to the titrator can cost the same as the titration installation, or even more. However, consider not only the costs for such an upgrade but also the many benefits.

I will now explain how the usage of a fully automated titration system can result in various savings.

 

Save valuable time

Time savings is one of the biggest benefits when using walk-away automation in the lab.

After preparing the sample and entering the required sample data into the controlling device, the system can run unattended for several hours or even days. During this time, lab technicians can spend their valuable time on samples that cannot be automated, evaluating data, preparing new samples, and documentation or inventing new methods or substances.

Don’t waste money on repetitions

In comparison to only using a stand-alone titrator, the automated system can reduce costs for repetitions. Due to the fact that the procedures have been tested before they are run autonomously, handling errors can be reduced to a minimum during the determination. These are typical tasks such as ensuring the sensor and buret tips are sufficiently covered by the sample solution, using the optimum stirring speed for the sample, as well as applying standardized cleaning procedures in between the analyses.

At first glance, these steps might not seem so important, but these have an impact if each lab technician involved in the analysis performs it in a slightly different manner based on their preference and experience. In the worst case, samples have to be repeated more often to prove the validity of the result. With automation, you no longer have to worry about this issue.

Reduce running expenses

The improved handling procedures mentioned above will reduce the costs for consumables such as electrodes. Thanks to the previously defined cleaning, conditioning, and storage procedures, the sensor lasts much longer. The only thing you have to consider is filling the electrolyte reservoir on a regular basis, which can not yet be automated.

However, if you are only running routine pH measurements, a solution already exists for this: the Ecotrode Gel, which allows you to run continuous measurements without any refilling until the electrolyte is exhausted.

The transparency of the electrolyte gel will show when it is time to change the electrode. Cool, isn’t it? 

Besides the electrodes, reagents and eventual waste disposal are topics that have to be taken into account when discussing the costs per analysis of an analytical device. Unfortunately, there are still several norms and standards using absurd amounts of organic solvents. All of these chemicals need a special treatment for proper disposal, i.e. the more waste solution produced, the higher the costs for its disposal—not to mention the impact on the environment.

In automated systems, the amount of these reagents can be reduced to a minimum as analyses can be carried out in beakers with a smaller diameter and perfectly positioned electrodes. Depending on the application, you can even reduce the cleaning procedure between the analyses to a simple dip in solvent rather than showering the electrode with an excess of solvent.

Fewer accidents thanks to walk-away automation

As an automated titration system runs independently for several hours or even overnight, the direct contact with harmful substances and reagents is already minimized. Modern titration systems do not only take over the analysis, but also guarantee the sample beakers are already pre-cleaned before you remove them from the system to put them in the dishwasher or dispose of them.

Even minimizing exposure to chemicals during the exchange of the reagents is possible if your system is equipped with 3S technology, which makes titrant change simpler than ever. The safer the system, the smaller the risk of exposure to hazardous chemicals while handling during sample analysis or disposal. 

We all know that an accident is one thing, but the administration afterwards can also be a real nightmare. Therefore, it is better to avoid situations prone to causing accidents, as it keeps people healthy and the associated costs down.

Increase your profit

Increasing the sample throughput has a direct impact on your profit. Without automation, more analysts are needed to handle the increasing number of samples, but finding well-educated lab technicians becomes ever more challenging and costly. Furthermore, boring routine titration analysis is not the work that lab staff desires.

Automation – not as expensive as you may have thought

Perhaps you started reading this blog post thinking that automation is too expensive for your lab, especially compared to the investment for a simple stand-alone titrator. However, as shown in this article, several kinds of savings can be achieved using an automated titration system.

Consider your regular expenses for consumables, reagents, and time spent for repeated analyses. How often were the results not available either fast or good enough for the production to continue? Think about discussions on safety in the lab when a colleague was injured. Also, how often was the efficiency and profitability of your lab questioned due to the running costs? Considering this, you will see the return on investment is unbelievably good with automation. The more samples you perform fully automated, the faster the initial investment pays off and creates better financial statements for you.

At Metrohm, we don’t just sell titrators. We provide titration solutionsWe offer systems as sophisticated or as straightforward as you need them. Titrator, accessories, electrodes, sample changers, and software – all from a single source.

Looking for a titrator?

Check out our selection here!

Post written by Heike Risse, PM Titration (Automation) at Metrohm International Headquarters, Herisau, Switzerland.

Measuring herbicides in drinking water

Measuring herbicides in drinking water

It’s springtime in the northern hemisphere, and with rising temperatures comes increased use of herbicides on agricultural crops and in public spaces. In March 2015, the International Agency for Research on Cancer (IARC) published a report which stated that one such herbicide, glyphosate, was «probably carcinogenic to humans». Ever since, the use of this chemical has been highly controversial. In some countries, including the USA, there are already limit values in effect for the weed killer.

Carcinogenic or not?

Glyphosate is a broad-spectrum herbicide used globally in agriculture. Alongside farming, the chemical is also used to kill weeds in domestic gardens and in public and private spaces kept free from «vegetal invasion», such as railway tracks.

Glyphosate has been used since the 1970s in pesticides and was previously thought to be harmless at typical levels of exposure. However, since the International Agency for Research on Cancer (IARC) – the specialized cancer-research agency of the WHO – found that glyphosate was «probably carcinogenic to humans» (Group 2A) in a report published in March 2015, the chemical repeatedly made headlines [1].

Experts were then divided over whether glyphosate should be reapproved after the expiry of its EU market approval on June 30, 2016. This is because the European Food Safety Authority (EFSA) only recently arrived at the opposed conclusion that it is unlikely that glyphosate is genotoxic or poses a carcinogenic threat [2]. The approval of glyphosate was initially extended by 18 months, but is now allowed to remain in use in the EU until at least the end of 2022 [3].

Determination of glyphosate in drinking water

Because chemicals used in farming can seep through the ground and enter the ground water, limit values are in effect in some countries concerning the concentration of glyphosate in drinking water.

Glyphosate and its metabolite AMPA (aminomethylphosphonic acid) are usually determined by HPLC with post-column derivatization and subsequent fluorescence detection (EPA Method 547), or alternatively by ion chromatography coupled with a mass-selective detector.

Methodology using IC

The following segments explain the initial results of the determination of glyphosate and AMPA in drinking water in the low µg/L range using ion chromatography (IC) with pulsed amperometric detection. The detection limits for glyphosate and AMPA previously attained with pulsed amperometric detection were around ≥ 50 µg/L [4].

Given this improvement in terms of sensitivity, the method outlined here represents a promising approach to the screening of water and food samples for glyphosate and AMPA.

Instrumentation

All determinations were performed with an IC system consisting of a 940 Professional IC Vario ONE with an IC Amperometric Detector and an 858 Professional Sample Processor for automatic sample injection (Figure 1).

Figure 1. Glyphosate and AMPA were determined with the ProfIC IC Vario 1 Amperometry system.

Glyphosate and AMPA were separated on the high-capacity anion separation column Metrosep Carb 2 – 150/4.0, and subsequently detected via flexIPAD (FLEXible Integrated Pulsed Amperometric Detection) using a gold working electrode as a measuring mode in the amperometric detector. The profile of the potential curve produced in one measuring cycle in flexIPAD mode is presented in Figure 2.

Figure 2. Pulse profile of the flexIPAD method: A measuring cycle lasts 0.9 s; measurement of the current is performed during the phase shown in red.

Experiment

The Metrosep Carb 2 column is used mainly for separating and determining carbohydrates, sugar alcohols, alcohols, etc. Its high column capacity, combined with the high pH value of the eluent (approximately pH 10), results in a large difference in retention time for AMPA and glyphosate. This is because, with a pH value of 10, all three acid groups are deprotonated in part of the glyphosate, meaning that it is partially present as a trivalent anion while the metabolite AMPA, which is missing the carboxyl group, is present as a divalent anion.

Results

Figure 3 shows the chromatogram of the determination of AMPA and glyphosate under the conditions used in this application. An aqueous standard solution was injected containing 10 µg/L each of both components.

Figure 3. Separation of AMPA and glyphosate: a standard solution containing 10 µg/L of each component in ultrapure water was analyzed.

The detection limits for both components were determined using the signal/noise (S/N) ratio, i.e., the ratio of the peak height to the baseline noise. At the detection limit, the S/N ratio is 3; with smaller values, secured detection is not possible. The detection limit found for AMPA was considerably lower than 1 µg/L, while the limit for glyphosate was approximately 1 µg/L.

Figure 4 shows a chromatogram of a drinking water sample mixed with 2 µg/L glyphosate and AMPA.

Figure 4. Determination of AMPA and glyphosate in drinking water which was mixed with 2 µg/L of each component.

Summary

For the first time, glyphosate and its primary metabolite AMPA were determined in drinking water in the low µg/L range using ion chromatography with pulsed amperometric detection (flexIPAD). This puts at our disposal a reliable and – compared with HPLC with a mass-selective detector – very inexpensive method for determining the glyphosate and AMPA content in water and foodstuffs. With a detection limit of approximately 1 µg/L, the adherence to limit values for glyphosate can be verified in the USA, Canada, and Australia, among others.

If you want to learn even more about how to measure glyphosate and AMPA via ion chromatography and amperometric detection, download our free white paper «Glyphosate and AMPA in drinking water».

Curious to learn even more?

Check out our webinar:

«Glyphosate and AMPA analysis»

References

[1] IARC Monographs Volume 112 (2015). Retrieved from http://monographs.iarc.fr/ENG/Monographs/vol112/mono112-09.pdf on June 27, 2016.

[2] EFSA press news, 151112 (2015). Retrieved from http://www.efsa.europa.eu/en/topics/factsheets/glyphosate151112 on June 27, 2016.

[3] European Commission: Status of glyphosate in the EU. Retrieved from https://ec.europa.eu/food/plant/pesticides/glyphosate_en on May 25, 2020.

[4] F. Sanchez-Bayo, R. V. Hyne, and K. L. Desseille (2010) Anal. Chim. Acta, 675 125–131.

Post written by Dr. Alyson Lanciki, Scientific Editor at Metrohm International Headquarters, Herisau, Switzerland.

Photometric complexometric titration

Photometric complexometric titration

…and how to choose the right wavelength for indication

Complexometric titration was discovered in 1945 when Gerold Schwarzenbach observed that aminocarboxylic acids form stable complexes with metal ions, which can change their color by addition of an indicator. From the 1950’s on, this technique gained popularity for the determination of water hardness. Soon it was clear that aside from magnesium and calcium, other metal ions could also be titrated in this way. The use of masking agents and new indicators gave further possibilities to determine not only the whole amount of metal ions present in solution, but also to separate and analyze them. A new titration type was born: complexometric titration.

Dear readers, have you ever performed a complexometric titration? According to my assumption, quite a lot of you will respond with “yes” as it is one of the most frequently used types of titration. However, I assume you probably struggled over the detection of the endpoint and over the titration itself. In contrast to other types of titrations, the boundary conditions such as pH and reaction time play an even bigger role in complexometry since the complex binding constant is very pH dependent and the reaction might be slow. This article presents the most common challenges and how to overcome them when carrying out complexometric titrations.

For a complexometric titration analysis, it is very important to know the qualitative composition of your sample. This determines the indicator, the complexing agent, and the masking agent you need to use.

Due to the length of the article, I have provided an easy legend of the topics so you can click and jump directly to the area that interests you the most.

Complexometric titration and complex-forming constant

Complexometric reactions always consist of a metal ion which reacts with a ligand to form a metal complex. Figure 1 shows an example of such a chemical reaction of a metal ion Mn+ with Ethylene diamine tetra acetic acid (EDTA). EDTA is the most commonly used titrant for complexometric titrations and reacts in a stoichiometric ratio of 1:1. As shown on the right side of Figure 1, EDTA can form six coordinational bonds, in different words: EDTA has a denticity of six. The more coordinational bonds a ligand can form, the more stable is the formed complex.

Figure 1. Example complexation reaction of a metal M with charge n+ with EDTA.

As with most chemical reactions, this type of reaction stays in an equilibrium. Depending on the metal ion used, this equilibrium can shift more to the left (reactants) or on the right (products) of the equation. For a titration, it is mandatory that the equilibrium is on the right side (complex-forming). The equilibrium constant is defined as shown in Equation 1.

Equation 1. Equilibrium constant, where c = concentration of the individual substances.

Equation 1 also illustrates why it is so important to keep the pH value constant. The concentration of hydronium ions influences the complex-forming constant by a factor of the square of its concentration (e.g., if one titrated with H2Na2EDTA). This means if the pH value of the reaction is changed, its complex-forming constant is also changed, which influences your titration.

Generally, the higher the concentration of the complex in comparison to the free metal / Ligand concentration, the higher the Kc and also the log(Kc) value. Some log(Kc) values are shown later on in Table 2 and can give you a hint regarding which titrant is most suitable for your titration.

Complexometric reactions are often conducted as a photometric titration. This means an indicator is added to the solution so that a color change at the endpoint can be observed. 

Color Indicator

As in acid–base titration, the color indicator is a molecule which indicates when the end of titration (the endpoint, or EP) is reached by a change in the solution color. For acid–base titration, the color change is induced by a change of pH, whereas in complexometric titration the color change is induced by the absence/presence of metal ions. Table 1 gives you an overview of different color indicators and the metals which can be determined with them.

Table 1. List of color indicators for different kinds of metal ions.

It is very important to choose the right indicator, especially when analyzing metal mixtures. By choosing an appropriate indicator, a separation of the metal ions can already take place.

As an example, consider a mixture of Zn2+ and Mg2+, which is titrated with EDTA. The log(Kc) value for the zinc ion is 16.5, and 8.8 for the magnesium ion. If we choose to titrate this sample with PAN-indicator then the indicator will selectively bind to the zinc, but not magnesium. As zinc has the higher complex-formation constant, the zinc ion will react first with EDTA, which will lead to a color change, and the endpoint can be detected. In such a case, the separation of the ions is possible. If this is not the case, the choice of a more suitable complexing agent might help you to obtain a separation of metal ions.

Complexing agent

At the beginning of your titration, the metal ions are freely accessible. By addition of the complexing agent (your titrant), the metal ions become bound. The prerequisite for that is a higher complex-formation constant of the metal with the complexing agent than with the indicator. In 95% of cases, this does not pose a problem. Some complexing agents are mentioned in Table 2. In general, ions with higher charges will have a higher complex-formation constant. 

However, what can you do if you are still not able to separate your metal ions sufficiently and determine them individually? The answer to that is: use a masking agent to make the second metal ion “invisible” to the titrant.

Table 2. Complex-formation constants log(Kc) of different complexing agents with various metal ions. The higher the number in the table the higher the binding strength between metal ion and ligand. As an example: aluminum binds stronger to DCTA than to EDTA.

Masking agents

In general, masking agents are substances which have a higher complex-formation constant with the metal ion than the complexing agent. Metal ions which react with the masking agent can no longer be titrated, and therefore the metal ion of interest (which does not react with the masking agent) can be determined separately in the mixture using the complexing agent. Table 3 shows a small selection of common masking agents. There are many more masking agents available which can be used for the separation of metal ions.

Table 3. A selection of different masking agents.

Complexometric titration is still often carried out manually, as the color change is easily visible. However, this leads to several problems. My previous post “Why your titration results aren’t reproducible: The main error sources in manual titration” explains the many challenges of manual titration.

Subjective color perception and different readings lead to systematic errors, which can be prevented by choosing a proper electrode or using an optical sensor, which accurately indicates the color change. This optical sensor changes its signal depending on the amount of light reaching the photodetector. It is usually the easiest choice when switching from manual titration to automated titration, because usually it does not require any changes to your SOP.

Which wavelength is optimal for indication?

Figure 2. The Optrode from Metrohm can detect changes in absorbance at 470, 502, 520, 574, 590, 610, 640, and 660 nm.

If you choose to automate your complexometric titration and indicate the color change with a proper sensor, you should use the Optrode. This sensor offers eight different wavelengths enabling its use with many different indicators.

Perhaps you’re asking yourself “why do I need eight different wavelengths”? The answer is simple. This sensor monitors the absorbance of a certain wavelength in the solution. Each wavelength change is best detected when the light is strongly absorbed by the color of the sample solution, either before or after the endpoint is reached. For example, during a color change from blue to yellow, it is recommended to select the wavelength 574 nm (yellow) for the detection of the color change, as it is the complementary color of blue. For even more accuracy, the optimal wavelength can be chosen by knowing the UV/VIS spectra of the indicator before and after complexation.

Figure 3. Left: spectra of complexed (purple) and uncomplexed (blue) Eriochrome Black T are shown. Right: the difference in absorption of the two spectra is shown.

On the left side of Figure 3 is a graph with the spectra of complexed and uncomplexed Eriochrome Black T. The uncomplexed solution has a blue tint, whereas the complexed one is more violet. On the right, another graph shows the difference of both spectra. According to this graph, the maximum difference in absorption is obtained at a wavelength of 660 nm. Therefore, it is recommended to use this wavelength for the detection of the color change.

For more examples of indicators and their spectra, check out our free monograph “Complexometric (Chelometric) Titrations”.

Challenges when performing complexometric titrations

As mentioned in the introduction, complexometric titrations are a bit more demanding compared to other types of titration.

First, the indicators themselves are normally pH indicators, and most complexation reactions are pH-dependent as well. For example, the titration of iron(III) is performed in acidic conditions, while the complexation of calcium can only take place under alkaline conditions. This leads to the fact that the pH has to be maintained constantly while performing complexometric titrations. Otherwise, the color change might not be visible, indicated incorrectly, or the complexation might not take place.

Second, complexation reactions do not occur immediately, as with e.g. precipitation reactions. The reaction might take some time. As an example, the complexation reaction of aluminum with EDTA can take up to ten minutes to be completed. Therefore it is also important to keep this factor in mind.

Perhaps a back-titration needs to be performed in such a case to increase accuracy and precision. Please have a look at our blog post “What to consider during back-titration” for more information about this topic.

Summary

Complexometric titrations are easy to perform as long as some important points are kept in mind:

  • If more than one type of metal is present in your sample, you might need to consider a masking agent or a more suitable pH range.
  • Reaction duration of your complexation reaction might be long. In this case, a back-titration or titration at elevated temperatures might be a better option.
  • Make sure that you maintain a stable pH during your titration. This can be achieved by addition of an adequate buffer solution.
  • Switching from manual to automated titration will increase accuracy and prevent common systematic errors. When using an optical sensor, make sure that you choose the right wavelength for the detection of the endpoint.

For a general overview of complexometric titration, have a look at Metrohm Application Bulletin AB-101 – Complexometric titrations with the Cu ISE.

For more detailed information

Download our free monograph:

Complexometric (Chelatometric) Titrations

Post written by Iris Kalkman, Product Specialist Titration at Metrohm International Headquarters, Herisau, Switzerland.

A History of Chemistry – Part 4

A History of Chemistry – Part 4

This article is the final installment in our four-part series on the history of chemistry. Did you miss the others? Don’t worry – you can find them all here:

The industrialization of electrochemistry

Michael Faraday (1791–1867) had a modest upbringing. He was 14 years old when he began his bookbinding apprenticeship. The young Faraday read a multitude of works that he received for binding and thus educated himself in the sciences as well as in literature and art. A customer at the bookbinding workshop noticed the curious apprentice and mentioned him to his father, who then took Faraday with him to several lectures given by electrochemistry pioneer Humphry Davy. Shortly after, Faraday began working for Davy.

As his assistant, Faraday traveled with Davy across Europe, as they carried out experiments together and met numerous influential scientists. Back in England, Faraday continued training as a chemist and in 1833 became a professor of chemistry. During this time, he investigated the basic laws of electrolysis. These formed the basis of electrochemistry and, in the second half of the century, enabled the development of an electrochemical industry which manufactured products such as chlorine, hydrogen, aluminum, magnesium, sodium, and potassium in its plants located at hydroelectric power stations.

Solvay’s soda ash

The industrial production of soda ash (sodium carbonate) had been possible since the development of the Leblanc process at the end of the 18th century. However, the synthesis required expensive raw materials and produced large amounts of the byproduct hydrogen chloride, which is toxic to the environment in which it is introduced. The produced hydrogen chloride escapes from industrial stacks and kills surrounding vegetation, and is also lethal to aquatic life when added to water.

During the second half of the 19th century, the Belgian Ernest Solvay (1838–1922) occupied himself with the issue. Solvay, who came from an industrialist family, had little formal education but was familiar with chemical procedures thanks to his work at his uncle’s and father’s factories. He developed the process for manufacturing soda ash, which was named after him and only has one byproduct – the harmless calcium chloride (CaCl2).

In 1861, Ernest Solvay and his brother Alfred began soda ash production in their own small factory in Brussels. By continuously adjusting the process, they became increasingly successful and continued to expand. Solvay, who had become very wealthy, became active in furthering scientific research and charitable causes. He also showed his sense of social responsibility in his factories: he established an eight-hour workday, paid holiday leave, a social security system, and a pension for his employees –long before it was legally mandatory.

The majority of the soda ash produced today is still created using the Solvay process.

Would you like to learn more?

Visit our site to read more about the Solvay process and the associated analysis techniques:

The periodic table of elements

There had already been 64 chemical elements had discovered by 1868. However, there was as yet no clear system of regulating which particular atom combinations formed new molecules. Sorting the elements based on their atomic mass had not offered a solution up to this point.

Dmitri Mendeleev (1834–1907) recognized a pattern here: when elements are sorted by their atomic mass, certain elemental properties are periodically repeated – specifically, after every eight elements. Mendeleev therefore retained the arrangement in ascending order of atomic mass, but then also sorted the elements that had the same properties below one another. Whenever properties were repeated after fewer than eight elements, he left open gaps to be filled with elements that had not yet been discovered. Mendeleev arranged the transition elements, which did not fit with his «octet rule», into their own column. This resulted in the first periodic table of elements in 1869.

From aniline to aspirin

Organic chemistry, which now went far beyond the synthesis of artificial urea, had become a significant and rapidly growing industry. The tar dye companies BASF, Bayer, and Hoechst, all of which were founded in the 1860s, grew so rapidly that they were employing thousands of people even before the turn of the century. From the end of the 19th century, the tar dye industry also developed synthetic organic medicinal products. Bayer, for example, patented the byproduct-free synthesis of acetylsalicylic acid in 1898 and marketed the product under the name «Aspirin» from the beginning of the 20th century.

In basic research, chemists began devoting themselves to increasingly complex organic molecules. Emil Fischer (1852–1919) investigated biologically significant molecules such as sugars and amino acids. In 1890, he used glycerin as a basis for synthesizing three sugars: glucose, fructose, and mannose. He later researched proteins. During this period, he discovered new amino acids and shed light on the type of bond which connects them to one another: an amide bond which he gave the name «peptide bond» [1].

First World War: Artificial fertilizer and warfare agents

The use of fertilizer had been common practice throughout agriculture ever since Liebig proved that it would improve yield. The nitrogen needed by plants for growth was added to fertilizers largely in the form of guano. This consists of the weathered excrement of seabirds which forms meter-thick layers over many years, particularly on the beaches of South America, where there are low levels of precipitation. In order to meet the high demand for food – and thus for fertilizer – entire shiploads of guano were being imported to Europe.

However, the import of guano could not keep pace with the rapid growth of population indefinitely, so at the end of the 19th century, researchers began looking for a way to fix nitrogen from the air. The German chemist Fritz Haber (1868–1934) eventually found a solution in 1909 and, with his ammonia synthesis, prevented the famine prophesied in the western world. Unfortunately, this development also enabled Germany’s production of warfare agents during the First World War, as ammonia could be used to create ammonium nitrate, which was then used in ammunition.

Fritz Haber
Carl Bosch

In the Haber-Bosch process, ammonia is produced as a result of a reaction between hydrogen and nitrogen. Fritz Haber achieved synthesis at a high temperature and a high pressure level, and with the aid of a catalyst. Carl Bosch (1874–1940) developed the industrial implementation of the process. For this purpose, he developed specific equipment made of state-of-the-art materials which could withstand both high pressure and temperature levels.

In 1914, the First World War broke out. The nations involved, as well as neutral states, faced blockades in their trade routes and had to become largely self-sufficient. Thanks to governmental structuring and aid, this led to a boom in industrial research across the globe. Numerous reputable scientists were actively involved in the war or supported it, including Fritz Haber, Walther Nernst, and Emil Fischer. In addition to the Haber-Bosch process, the pressure to create innovations that prevailed before and during the war also resulted in the first synthetic rubber as well as mustard gas and the toxic gas phosgene. Chlorine gas, which is produced during ammonia synthesis, was also used as a warfare agent during World War One.

What if . . .

. . . the Haber-Bosch process didn’t exist? Without the nitrogen fertilizer produced using the Haber-Bosch process, there would likely be a lot fewer people on Earth: the population growth of around 1.6 billion in 1900 to nearly 8 billion today would not have been possible without yield improvements brought about by artificial nitrogen fertilizers. Agriculture is still dependent on it today: without this process, the planet would only be able to provide enough food for half the population [2].

Chemistry since WWI

Following the armistice agreement in 1918, the German chemical industry – which had been world-leading until then – lost all of its patents and had to reveal numerous production secrets in order to satisfy the reparation demands of the victorious Allied Powers [3]. The German chemical industry, which had been the world’s largest at the time, had to relinquish its place at the top. Although it experienced another upswing toward the beginning of the Second World War, today’s leading lights in the chemical industry are the USA and France. During the post-war period, polymer chemistry and pharmaceutical chemistry were the fields that saw particular advancement and brought about countless products which are still essentials today. Among these are polymers, including synthetic fibers such as nylon and polyester, and artificially produced vitamins and hormones.

The time around the turn of the 20th century saw rapid advancement in chemistry, both in fundamental research as well as in industry – and to a great extent, it is the relationship between the two which enabled this progress. Numerous processes developed during this time period, including the Haber-Bosch and Solvay processes, have remained the methods of choice in the production of chemicals – in this case ammonia and soda ash, respectively – to this very day. 

References

[1] The Components of Life: From Nucleic Acids to Carbohydrates; 1st ed., Rogers, K., Ed.; Britannica Educational Publishing/Rosen Educational Services: New York, 2011; p 59.

[2] Erisman, J. W., Sutton, M. A., Galloway, J., Klimont, Z., and Winiwarter, W. (2008) Nat. Geosci. 1, 636–639.

[3] Kricheldorf, H. R. Menschen und ihre Materialien: Von der Steinzeit bis heute; 1st ed., Wiley-VCH Verlag & Co. KGaA: Weinheim, 2012; p 111.

Post written by Dr. Alyson Lanciki, Scientific Editor at Metrohm International Headquarters, Herisau, Switzerland. Primary research and content contribution done by Stephanie Kappes.

What to consider during back-titration

What to consider during back-titration

Titrations can be classified in various ways: by their chemical reaction (e.g., acid-base titration or redox titration), the indication method (e.g., potentiometric titration or photometric titration), and last but not least by their titration principle (direct titration or indirect titration). In this article, I want to elaborate on a specific titration principle – the back-titration – which is also called «residual titration». Learn more about when it is used and how you should calculate results when using the back-titration principle.

What is a back-titration?

In contrast to direct titrations, where analyte A directly reacts with titrant T, back-titrations are a subcategory of indirect titrations. Indirect titrations are used when, for example, no suitable sensor is available or the reaction is too slow for a practical direct titration.

During a back-titration, an exact volume of reagent B is added to the analyte A. Reagent B is usually a common titrant itself. The amount of reagent B is chosen in such a way that an excess remains after its interaction with analyte A. This excess is then titrated with titrant T. The amount of analyte A can then be determined from the difference between the added amount of reagent B and the remaining excess of reagent B.

As with any titration, both involved reactions must be quantitative, and stoichiometric factors involved for both reactions must be known.

Figure 1. Reaction principle of a back-titration: Reagent B is added in excess to analyte A. After a defined waiting period which allows for the reaction between A and B, the excess of reagent B is titrated with titrant T.

When are back-titrations used?

Back titrations are mainly used in the following cases:

  • if the analyte is volatile (e.g., NH3) or an insoluble salt (e.g., Li2CO3)
  • if the reaction between analyte A and titrant T is too slow for a practical direct titration
  • if weak acid – weak base reactions are involved
  • when no suitable indication method is available for a direct titration

Typical examples are complexometric titrations, for example aluminum with EDTA. This direct titration is only feasible at elevated temperatures. However, adding EDTA in excess to aluminum and back-titrating the residual EDTA with copper sulfate allows a titration at room temperature. This is not only true for aluminum, but for other metals as well.

Learn which metals can be titrated directly, and for which a back-titration is more feasible in our free monograph on complexometric titration.

Other examples include the saponification value and iodine value for edible fats and oils. For the saponification value, ethanolic KOH is added in excess to the fat or oil. After a determined refluxing time to saponify the oil or fat, the remaining excess is back-titrated with hydrochloric acid. The process is similar for the iodine value, where the remaining excess of iodine chloride (Wijs-solution) is back-titrated with sodium thiosulfate.

For more information on the analysis of edible fats and oils, take a look at our corresponding free Application Bulletin AB-141.

How is a back-titration performed?

A back titration is performed according to the following general principle:

  1. Add reagent B in excess to analyte A.
  2. Allow reagent B to react with analyte A. This might require a certain waiting time or even refluxing (e.g., saponification value).
  3. Titration of remaining excess of reagent B with titrant T.

For the first step, it is important to precisely add the volume of reagent B. Therefore, it is important to use a buret for this addition (Fig. 2).

Figure 2. Example of a Titrator equipped with an additional buret for the addition of reagent B.

Furthermore, it is important that the exact molar amount of reagent B is known. This can be achieved in two ways. The first way is to carry out a blank determination in the same manner as the back-titration of the sample, however, omitting the sample. If reagent B is a common titrant (e.g., EDTA), it is also possible to carry out a standardization of reagent B before the back-titration.

In any case, as standardization of titrant T is required. This then gives us the following two general analysis procedures:

Back-titration with blank
  1. Titer determination of titrant T
  2. Blank determination (back-titration omitting sample)
  3. Back-titration of sample
Back-titration with standardizations
  1. Titer determination of titrant T
  2. Titer determination of reagent B
  3. Back-titration of sample

Be aware: since you are performing a back-titration, the blank volume will be larger than the equivalence point (EP) volume, unlike a blank in a direct titration. This is why the EP volume must be subtracted from the blank or the added volume of reagent B, respectively.

For more information on titrant standardization, please have a look at our blog entry on this topic.

How to calculate the result for a back-titration?

As with direct titrations, to calculate the result of a back-titration it is necessary to know the involved stoichiometric reactions, aside from the exact concentrations and the volumes. Depending on which analysis procedure described above is used, the calculation of the result is slightly different.

For a back-titration with a blank, use the following formula to obtain a result in mass-%:

VBlank:  Volume of the equivalence point from the blank determination in mL

VEP Volume at the equivalence point in mL

cTitrant:  Nominal titrant concentration in mol/L

fTitrant Titer factor of the titrant (unitless)

r:  Stoichiometric ratio (unitless)

MA Molecular weight of analyte A in g/mol

mSample Weight of sample in mg

100:  Conversion factor, to obtain the result in %

The stoichiometric ratio r considers both reactions, analyte A with reagent B and reagent B with titrant T. If the stoichiometric factor is always 1, such as for complexometric back-titrations or the saponification value, then the reaction ratio is also 1. However, if the stoichiometric factor for one reaction is not equal to 1, then the reaction ratio must be determined. The reaction ratio can be determined in the following manner:

 

  1. Reaction equation between A and B
  2. Reaction equation between B and T
  3. Multiplication of the two reaction quotients
Example 1

Reaction ratio: 

Example 2

Reaction ratio: 

Below is an actual example of lithium carbonate, which can be determined by back-titration using sulfuric acid and sodium hydroxide.

The lithium carbonate reacts in a 1:1 ratio with sulfuric acid. To determine the excess sulfuric acid, two moles of sodium hydroxide are required per mole of sulfuric acid, resulting in a 1:2 ratio. This gives a stoichiometric ratio r of 0.5 for this titration.

 For a back-titration with a standardization of reagent B, use the following formula to obtain a result in mass-%:

VB Added volume of the reagent B in mL

cB:  Nominal concentration of reagent B in mol/L

fB:  Titer factor of reagent B (unitless)

VEP:  Volume at the equivalence point in mL

cT:  Nominal concentration of titrant T in mol/L

fT Titer factor of the titrant T (unitless)

sBT Stoichiometric factor between reagent B and titrant T

sAB:  Stoichiometric factor between analyte A and reagent B

MA:  Molecular weight of analyte A in g/mol

mSample:  Weight of sample in mg

100:  Conversion factor, to obtain the result in %

Modern titrators are capable of automatically calculating the results of back-titrations. All information concerning the used variables (e.g., blank value) are stored together with the result for full traceability.

To summarize:

Back-titrations are not so different from regular titrations, and the same general principles apply. The following points are necessary for a back-titration: 

  • Know the stoichiometric reactions between your analyte and reagent B, as well as between reagent B and titrant T.
  • Know the exact concentration of your titrant T.
  • Know the exact concentration of your reagent B, or carry out a blank determination.
  • Use appropriate titration parameters depending on your analysis.

If you want to learn more about how you can improve your titration, have a look at our blog entry “How to transfer manual titration to autotitration”, where you can find practical tips about how to improve your titrations.

If you are unsure how to determine the exact concentration of your titrant T or reagent B by standardization, then take a look at our blog entry “What to consider when standardizing titrant”.

Post written by Lucia Meier, Product Specialist Titration at Metrohm International Headquarters, Herisau, Switzerland.

A History of Chemistry – Part 3

A History of Chemistry – Part 3

This article is the third in our four-part series on the history of chemistry. Missed the first two? Don’t worry – you can read both of them here:

Chemistry and society: An explosive pair

It is the early 19th century, and industrialization in Europe is in full swing. Close collaboration between the chemical industry and research – largely in France to start with, then followed by other European countries – is resulting in rapid advances in both sectors. As the chemical industry grows, chemistry is gaining a higher profile in society. The third and fourth parts of our series on the history of chemistry consider the relationship between chemistry, industry, and society from the 19th century onward.

The chemistry of living organisms

One of the most important chemists of the early 19th century is Jöns Jakob Berzelius (1779–1848). This Swedish scientist improved laboratory techniques and developed methods for elemental analysis. By conducting systematic analyses on a large scale, he determined the molecular formulae of virtually all known inorganic compounds and the atomic masses of the elements that had been discovered at that point. He is also the person we have to thank for element symbols: H for hydrogen, O for oxygen, and so on. The only difference between his notation and what we use today is that Berzelius presented element proportions in molecular formulae as superscript characters rather than the subscript characters we see nowadays (e.g., H2O instead of H2O). 

As well as this, he dealt extensively with the chemistry of organisms, something which he dubbed «organic chemistry». Being a proponent of vitalism, Berzelius was convinced that only living organisms were capable of producing organic substances, claiming that «vital force» was necessary for this process. The findings of one of his apprentices, Friedrich Wöhler, would later put a question mark on this hypothesis.

Organic from inorganic – is it possible?

In 1828, Friedrich Wöhler (1800–1882) was the first person who successfully managed to synthesize an organic compound from inorganic reagents: by heating ammonium cyanate, he was able to create its organic isomer, urea. He thus showed that organic substances can be created in a laboratory and that humans are therefore able to imitate and manipulate nature. More and more organic syntheses were made possible as the 19th century progressed.

Wöhler’s synthesis of urea was revolutionary. Today, urea is produced industrially at a rate of 150 million tons per year. Among other things, it is used for dermatological products and in the polymer industry.

Metrohm offers you solutions for the determination of urea and its contaminants. To find out more, visit our industry page «Chemical» and choose «Basic chemicals»:

Wöhler and Liebig: A fruitful friendship

Wöhler formed a friendship with Justus von Liebig (1803–1873) after they settled a dispute about silver fulminate and silver cyanate in 1825. Both substances share the same molecular formula, but the silver fulminate discovered by Liebig is highly explosive, whereas Wöhler’s silver cyanate is not. They eventually ascertained that the type and number of atoms in a compound alone are not enough to characterize a substance – the arrangement of the atoms must also be considered. As well as a spirit of mutual esteem, Liebig and Wöhler thus discovered isomerism. However, determining the molecular structure was not yet possible at that time.

In 1832, the two researchers worked together to formulate their so-called radical theory, which paved the way for modern organic chemistry. This stated that organic substances are composed of atom groups, which they called radicals. These remain unchanged during chemical reactions and are merely exchanged between the reactants. Although the term «radical» now has a different meaning in chemistry, a very similar principle remains until today: functional groups.

Superphosphate revolutionizes agriculture

Around 1840, Liebig, who had studied at the Sorbonne in Paris under such great names as Gay-Lussac and experienced France’s symbiotic relationship between science and industry, turned his back on fundamental research. Instead, he began studying organic chemistry in physiology and agriculture. He realized that plants extract nutrients needed for growth from the ground – with the exception of carbon dioxide, sourced from the air. From his findings, he deduced practical implications which revolutionized agriculture. Through his work, Liebig was the first to establish the need for fertilizer from a scientific point of view. His research also allowed him to determine which nutrients need to be present in fertilizer. This included simple organic compounds, but also inorganic substances such as salts. Based on this knowledge, Liebig developed the first artificial fertilizer, superphosphate, which led to an enormous increase in agricultural yields.

Liebig’s superphosphate fertilizer is still used today. Thanks to new findings, however, there are now a multitude of fertilizers which can provide the necessary nutrients based on the plants and soil conditions.

You can find several free Metrohm applications for agrochemicals available for download here:

Kekulé: dreamer or fibber?

Liebig’s students carried on his legacy through conducting fundamental chemical research. One such example is August Kekulé (1829–1896), who was inspired by Liebig to study chemistry during his time at the University of Giessen instead of becoming an architect as Kekulé’s family had envisaged. In 1858, Kekulé recognized the ability of carbon atoms to bond directly with one another to form chains. This explained how the few elements found in organic matter could form such a diversity of organic substances. In 1865, Kekulé also published findings on the structure of benzene.

According to his own statements, both of Kekulé’s groundbreaking ideas were inspirations from dreams – but the truth behind this is disputed. Kekulé is regarded as an intellectual who disparaged the culture prevailing among chemists and industrialists at the time: a pragmatic, positivistic way of thinking was spreading – it was a blind sense of empiricism which afforded no room for imagination. Christoph Meinel – a historian of chemical sciences – doubts the truth behind the dream anecdote, first told by Kekulé during a speech at a celebration in his honor. He states: «Kekulé’s ambivalent attitude toward the mentality present during this historical period, known as the ‹Gründerzeit›, and toward the patriarchal views of Berlin society resonates only too clearly in his speech. When Kekulé finishes narrating his vision with the words ‹Let’s learn to dream, gentlemen!›, the irony is very difficult to ignore given the prominent profile of those in attendance, who represented Prussian bureaucracy, Gründerzeit industries, and the elitist universities of the time» [1].

Artificial colors: All thanks to benzene

Regardless of whether Kekulé’s anecdote was based on true events or not, his discovery of the benzene structure and its importance to chemistry cannot be denied. Knowledge of organic and aromatic structures enabled systematic synthesis of the same molecules. The work of chemists was increasingly shifting from the isolation of substances from nature to the synthesis of artificial substances. The colorant industry experienced a boom after the discovery of the benzene structure, as this meant that a multitude of artificial colors could now be produced. Indigo production, for example, became an economically significant industrial process.

Colorant syntheses have not lost relevance since their invention in around 1900 – in fact, quite the opposite case. Colorants have been continuously developed for numerous properties and functions. This makes them inherently more complex than their primitive predecessors.

You can find out which analysis technique you need to monitor colorant properties on our industry page «Chemical» under the menu item «Solvents and colorants»: 

Check out the blog next week for the final installment of the series to learn about the advancements of chemistry around World War II.

Reference

[1] Sponsel, R. and Rathsmann-Sponsel, I. Kekulés Traum. Über eine typisch-psychoanalytische Entgleisung Alexander Mitscherlichs über den bedeutenden Naturwissenschaftler und Chemiker August Kekulé (1829-1896), Mitschöpfer der Valenz-, Vollender der Strukturtheorie und Entdecker der Bedeutung des Benzolrings. Alternative Analyse und Deutung aus allgemeiner und integrativer psychologisch-psychotherapeutischer Sicht. http://www.sgipt.org/th_schul/pa/kek/pak_kek0.htm (accessed Aug 15, 2016).

Post written by Dr. Alyson Lanciki, Scientific Editor at Metrohm International Headquarters, Herisau, Switzerland. Primary research and content contribution done by Stephanie Kappes.