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Exposing secrets of ancient Greek civilization through chemistry

Exposing secrets of ancient Greek civilization through chemistry

This week, learn the story of how analytical instrumentation from Metrohm helps underwater archaeology locate hidden treasures beneath the seafloor.

 

Antikythera Mechanism: a machine lost to time

One of the most fascinating items ever salvaged from an ancient shipwreck is the so-called «Antikythera Mechanism». More than 2000 years old, this magnificent piece of mechanical engineering forced the scientific community to rewrite the history of science as it became clear that its unknown maker must have possessed knowledge and skills that were believed to simply not exist in the 1st century BC.

Figure 1. Digital reconstruction of the Antikythera Mechanism.

The Antikythera Mechanism was a complex and highly precise lunar and solar calendar that could also predict solar and lunar eclipses as well as the future dates of the Panhellenic Games. The complexity and precision of this machine inspired not only scientists but also Hublot, the Swiss brand famous for their luxury watches. Not only did Hublot recreate the Antikythera Mechanism in a wristwatch but they also started their own underwater archaeology program. This project of Hublot is fascinating—and we from Metrohm are part of it on every dive.

 The device was retrieved from an ancient shipwreck (70 BC) found off the coast of the Greek island of Antikythera in 1901. Since then, researchers have tried to get to the bottom of its mysteries. Dated to approximately 100 BC, the Antikythera Mechanism was a shockingly complex piece of machinery, the likes of which were not seen elsewhere for at least another millennium.

One of the challenges faced by underwater archeology is the fact that the cargo and debris of ancient shipwrecks is often randomly scattered across vast areas on the seafloor and also often covered by sediments. Because only fragments of the mechanism have been found and recovered, retrieving the missing pieces of the Antikythera Mechanism would be a scientific sensation.

Figure 2. Location where the Antikythera Mechanism was found in 1901 at a shipwreck in Greece.

As divers can only operate for very limited time spans at depths below 50 meters, drones are needed to investigate larger areas on the seafloor at such depths. Hublot’s engineers have built drones for this purpose, known as «Bubblots», and have equipped them with miniaturized voltammetric measuring stands from Metrohm.

«With a metal detector, all you get is «beep-beep-beep», which means there is metal around. However, in a bronze statue, there is copper, there is tin, and you have to detect the oxides of them, the exact kind of material you are facing. We have decided for Metrohm, because you are the most competent for the measuring technology we need in our drones.»

Mathias Buttet

R&D Director, Hublot

The Bubblots are utilized to perform real-time analyses of the seawater for unusual concentrations of dissolved metal salts typically associated with corroding bronze artefacts. Thus, the systematic and highly selective investigation of larger areas of seafloor for historical bronze artefacts becomes feasible.

Figure 3. Hublot’s underwater drones, known as «Bubblots», and the voltammetric measuring stand from Metrohm.

Voltammetry to the rescue

Due to its selectivity regarding different metals and their oxidation states, voltammetry is ideally suited for such investigations, as it is also very fast and robust technique. In the case of Hublot’s drones, results are obtained in a few seconds and this information can be immediately processed.

«We use this Metrohm instrument for voltammetric measurements. We take a water sample and do a live measurement of the aspirated water. The voltammetric measurement takes only a few seconds. This is enough to give us an idea of the different metals present in the solution. This allows us to do highly selective measurements very fast to cover different regions of the archaeological site.»

Sébastien Recalcati

Materials Engineer, Hublot

For a selection of free Metrohm Application Notes related to voltammetric measurements in seawater, visit our website!

Figure 4. The 910 PSTAT mini from Metrohm used in the study.
Figure 5. One of Metrohm’s disposable screen printed electrodes (SPEs) utilized in Hublot’s drone analysis of the seafloor.

Giving the Antikythera Mechanism a second life

The maker of this mechanism was far ahead of his time. He must have had skills and possessed scientific knowledge that are mind-boggling even today. The watchmakers from Hublot were inspired by this to a very special project: they rebuilt the Antikythera Mechanism in a wristwatch.

«The original Antikythera Mechanism has the size of a shoe box. Reducing the size of the mechanism and putting it into a wrist watch was not so easy. Because the Antikythera Mechanism was not a clock, it was a machine with a driving crank to show the position of the moon and the sun in relation to the stars at any given date. The absolute dream is to find the missing parts of the machine. But the debris is hidden below the seafloor, covered by sediments, one meter, sometimes two meters.»

Mathias Buttet

R&D Director, Hublot

Figure 6. The Antikythera Mechanism miniaturized and captured in a Hublot wristwatch.

We are glad to support Hublot’s archaeological mission with our analytical instruments and our expertise in chemical analysis. Metrohm wishes the Hublot team all the best.

Visit our website to learn more

about this fascinating project and to discover more related applications from Metrohm

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

Trace metal analysis with solid-state electrodes – Part 3

Trace metal analysis with solid-state electrodes – Part 3

In Part 2 of this series on trace metal analysis with solid-state electrodes, we introduced the scTRACE Gold electrode. The third part of this series explains even more applications which can be performed with this electrode, but this time after modifying the gold micro-wire with a thin layer of another metal.

Catch up on the series «Trace metal analysis with solid-state electrodes» here:

Why modify the electrode material?

As explained for the Bi drop electrode in Part 1 of this series, stripping voltammetry is a two-step measurement.

In the first step, the analyte is deposited on the working electrode. In the case of anodic stripping voltammetry (ASV), the analyte is reduced and forms an alloy with the electrode material (Fig. 1). In the case of adsorptive stripping voltammetry (AdSV), the analyte forms a complex which is adsorbed to the working electrode.

In the subsequent stripping step, the deposit is brought back into solution, giving the analytical signal which is proportional to the deposited amount of analyte. In the case of ASV, the electrochemical reaction is the re-oxidation of the analyte during an anodic scan (Fig. 2). In the case of AdSV, the adsorbed metal complex is reduced during a cathodic scan.

Figure 1. Anodic stripping voltammetry (ASV) with Ag film modified scTrace Gold electrode – deposition of lead (solution stirred).

Figure 2. Anodic stripping voltammetry (ASV) with Ag film modified scTrace Gold electrode – stripping of lead (solution not stirred).

Both steps, deposition as well as stripping, are subject to the principles of kinetics and thermodynamics. Without going into detail, the result is simply that some analytes cannot be determined with certain electrode materials. One way to solve this problem is to modify an existing working electrode with a different material that is more suitable.

Applications

Lead in drinking water

Most of the lead which is present in surface and ground water is of anthropogenic origin, resulting from the leaching of contaminated soils. Lead in tap water, however, often originates from the household plumbing system. Pipes from lead metal were popular in some countries until the 1970s. Although Pb is barely soluble in water, it slowly dissolves in the presence of oxygen. As a result, the allowed limit for lead in tap water can be easily exceeded by a significant amount. Now lead pipes for municipal water transport are forbidden, but there are still houses with old installations intact. The WHO (World Health Organization) recommends a limit value for lead in drinking water of 10 µg/L. In the European Union, the upcoming limit is as low as 5 µg/L.

For the determination of lead, the scTRACE Gold electrode is modified with a silver film. The film is plated ex situ from a separate plating solution. Once plated, it can be used for multiple determinations. When the film is depleted, it can be removed, and then a fresh film is plated again. A side effect of the silver film is that the scTRACE Gold electrode lasts longer, since aging processes mainly affect the renewable silver film. In a repeatability study, determining 10 µg/L Pb with 3 different electrodes on 4 different days (total number of determinations = 10) the average recovery of Pb was 96% with a relative standard deviation of 5%.

Using the 884 Professional VA it is possible to measure lead concentrations in water down to 0.4 µg/L, allowing a simple and reliable determination of even the future limit in the European Union.

With the 946 Portable VA Analyzer, the limit of detection is only slightly higher: 0.6 µg/L. However, the mobile use offers the possibility for close monitoring of individual installations without the need to preserve samples and send them in to a central lab. Furthermore, the concerned resident gets an immediate result on the spot.

Free Application Note download: AN-V-214 Lead in drinking water – Straightforward determination by voltammetry using a gold microwire electrode.

If you want to learn more about our voltammetry product lines, lab as well as mobile, check out our website!

Nickel and cobalt in drinking water

Similar to lead, nickel concentrations present in water sources can be increased by human influence as well. Plumbing fixtures and faucets are often plated with a thin layer of nickel for protection against corrosion, even if the finish is made of chromium. Furthermore, nickel is part of many alloys from stainless steel to nickel brasses and bronze. Nickel steel alloy cookware or nickel pigmented dishes can also cause increased nickel levels. The maximum allowed level in drinking water in the European Union is 20 µg/L whereas the WHO recommends a limit of 70 µg/L.

For the voltammetric determination of nickel and cobalt, an ex situ plated bismuth film on the scTRACE Gold electrode is used as working electrode. Nickel as well as cobalt are determined in the form of their DMG (dimethylglyoxime) complex. This method had already proven its reliability with the mercury electrode, and therefore this application can now be transferred to a mercury-free electrode. With a detection limit of 1 µg/L with the 946 Portable Analyzer, and even lower at 0.2 µg/L with the 884 Professional VA lab instrument, the method is surely sufficient to monitor the compliance with legal requirements. The recovery for 1 µg/L Ni in a standard solution is about 99% (mean of 10 determinations) with a relative standard deviation of 5%.

Free Application Note download: AN-V-217 Nickel, cobalt in drinking water – Straightforward determination by voltammetry using a gold microwire electrode.

Chromium(VI) in drinking water

The problem of chromium(VI) in drinking water was brought to the attention of the general public with the movie «Erin Brockovich» in 2000, starring Julia Roberts. The plot is based on a true story, which happened in the small community of Hinkley, California, where the local energy provider contaminated the groundwater with the carcinogenic hexavalent chromium. The company attempted to cover up the incident, but an increased number of tumors and other health problems among the residents could finally be traced back to the contaminated drinking water.

Contamination with Cr(VI) in the environment is usually the result of improper handling of various industrial processes, especially abandoned waste dumped from galvanic chromium plating. The WHO recommends a maximum limit of 50 µg/L total chromium for drinking water

After modifying the scTRACE Gold electrode with an ex situ plated mercury film, Chromium(VI) can be determined as a complex with DTPA (diethylenetriaminepentaacetic acid). The recovery of a standard containing 30 µg/L Cr(VI) is 115% (mean of 3 determinations) with a relative standard deviation of 2%. Using the 946 Portable VA Analyzer it possible to determine concentrations down to 2 µg/L Cr(VI), allowing the on-site determination, providing immediate results without delay.

Free Application Note download: AN-V-230 Chromium(VI) in drinking water – Sensitive determination on the mercury film modified scTRACE Gold (DTPA method).

Summary

Talking about all of the applications that are possible with the scTRACE Gold electrode would go beyond the scope of this blog. The table here gives an overview of several elements for which methods with the scTRACE Gold are currently available from Metrohm. Your local Metrohm representative can assist in case of questions regarding the determination of one of the elements, or analysis in a specific matrix.

Figure 3. The scTRACE Gold electrode from Metrohm is suitable for trace analysis of several elements in water.

Overview: Applications with the scTRACE Gold
Element Application document
As(total) Application Note V-210
As(III) Application Note V-211
Hg Application Note V-212
Cu Application Note V-213
Pb Application Note V-214
Zn Application Note V-215
Tl Application Note V-228
Fe Application Note V-216
Ni, Co Application Note V-217
Bi Application Note V-218
Sb(III) Application Note V-229
Cr(VI) Application Note V-230

What’s next?

In Part 4 of this series, I will discuss the use of screen-printed electrodes (SPEs) which had already been introduced in the blog post «Virus detection using screen-printed electrodes». However, this time the focus will be on the determination of heavy metals using these disposable electrodes.

Post written by Barbara ZumbrägelProduct Manager VA/CVS at Metrohm International Headquarters, Herisau, Switzerland.

Forewarned is Forearmed: Error and risk minimization in process analysis – Part 3

Forewarned is Forearmed: Error and risk minimization in process analysis – Part 3

In the course of life, each of us learns to trust our gut feelings or our experiences to avoid situations that seem dangerous or risky. You quite literally sense potential dangers with an uneasy feeling. Who hasn’t painfully learned that touching a hot stove top isn’t a good idea? Or who voluntarily goes outside during a tornado?

While humans can rely on their intuition and learned patterns to avoid dangers or use protective strategies, this is far more complicated with electronic systems or machines. All components of a system must be in a permanently safe state. Failures and malfunctions of individual components can have devastating consequences for production processes and the safety of the operators.

An example of this is the Seveso disaster in 1976, in which highly toxic dioxin TCDD escaped as a result of an uncontrolled reaction, and sustainably poisoned flora and fauna. With regard to other major chemical accidents, the European Seveso III Directive then came into force in 2012 to control major accident hazards to prevent major accidents.

Have you read Part 1 and Part 2 of our «Advantages of PAT (Process Analytical Technology)» series? If not, find them here!

Recognize, master, and avoid errors

Process engineering systems that are operated continuously contain countless components that can wear out or fail during their life cycle. However, if the measuring, control, or regulating circuit is affected, failures can cause immense damage. Under no circumstances should humans nor the environment be exposed to any kind of danger. For this reason, the functional safety of the components must be guaranteed, and their risk and hazard potential must be analyzed in detail.

The service life of mechanical components can be evaluated by observing mechanical wear and tear. However, the aging behavior of electronic components is difficult to assess. A unit of measure that makes risk reduction and thus functional safety quantifiable is the so-called «Safety Integrity Level» (SIL). 

The following procedure is followed:

  1.   Risk analysis
  2.   Realization of risk reduction
  3.   Evidence that the realized risk reduction corresponds at least to the required risk reduction

«Process analysis systems are part of the entire safety cycle of a manufacturing plant and therefore only one component whose risk of malfunctions and failures must be considered in an assessment.»

Risk assessmentA process is considered safe if the current risk has been reduced below the level of the tolerable risk. If safety is ensured by technical measures, one speaks of functional safety.

Significance for process analysis systems

Errors can happen anywhere, and can never be completely excluded. To minimize possible errors, it is therefore necessary to estimate the risk of occurrence and the damage to be expected from it as part of a risk analysis. A distinction must be made here between systematic and random errors.

Systematic errors are potentially avoidable and are caused, for example, by software errors or configuration deficiencies. Accordingly, they already exist during or prior to commissioning.

In contrast, random errors are potentially difficult to avoid because they occur arbitrarily. Nevertheless, the error rate or failure probability can be determined statistically and experimentally.

Random errors usually result from the hardware and occur during operation. Ultimately, systematic errors should be avoided, and random errors should be mastered to ensure trouble-free functionality.

Process analysis systems are the link between manual laboratory analysis and the industrial process. In applications where continuous and fully automatic monitoring of critical parameters is required, process analyzers are indispensable. Due to the different analysis conditions in the laboratory and directly in the process, there are some challenges when transferring the measurement technology from the lab to the process. The decisive factors are the working and environmental conditions (e.g., high temperatures, corrosive atmospheres, moisture, dust, or potentially explosive environments) which the process analyzers have to meet regarding their design, construction materials, and reliability of the components. The analyzer automatically and continuously transmits system and diagnostic data to prevent hardware or software components from failing through preventive measures. This significantly reduces the chance of random errors occurring.

General process analyzer setup

a) Analyzer Setup

Process analyzers have been specially developed for use in harsh and aggressive industrial environments. The IP66 protected housing is divided into two parts, and consists of separate wet and electronic parts. The electronics part contains all components relevant to control and operate the process analyzer. Modular components like burettes, valves, pumps, sampling systems, titration vessels, and electrodes can be found in the analyzer wet part. Representative samples can thus be taken from the process measuring point several meters away. The analysis procedure, the methods to be used, and method calculations are freely programmable.

A touchscreen with intuitive menu navigation allows easy operation, so that production processes can be optimized at any time. The course of the measurement is graphically represented and documented over the entire determination, so that the analysis process is completely controlled. The measurement results can be generated 24/7 and allow close and fully automatic monitoring of the process. Limits, alarms, or results are reliably transferred to the process control system.

When operating the analyzer, there is a risk that software errors can lead to failures. In order to recognize this with foresight, the system delivers self-diagnostic procedures as soon as it is powered on and also during operation. This includes, e.g., checking pumps and burettes, checking for leaks, or checking the communication between the I/O controller, the human interface, and the respective analysis module.

b) Sensors

The central component of a process analyzer is the measurement technique in use. In the case of sensors or electrodes, there are several requirements such as chemical resistance, ease of maintenance, robustness, or precision which they must meet. The safety-related risk arises from the possibility if measurement sensors fail due to aging, or if they become damaged and subsequently deliver incorrect measurement results.

Failure of the electrode, contamination, or damage must be reported immediately. With online analysis systems, the analysis is performed in an external measuring cell. In addition, recurring calibration and conditioning routines are predefined and are performed automatically. The status of the electrode is continuously monitored by the system.

Between measurements, the electrode is immersed in a membrane-friendly storage solution that prevents drying out and at the same time regenerates the swelling layer. The electrode is therefore always ready for use and does not have to be removed from the process for maintenance. This enables reliable process control even under harsh industrial conditions.

c) Analysis

Process analyzers must be able to handle samples for analysis over a wide concentration range (from % down to trace levels) without causing carry-over or cross-sensitivity issues. In many cases, different samples from several measuring points are determined in parallel in one system using different analysis techniques. The sample preparation (e.g., filtering, diluting, or wet chemical digestion) must be just as reliable and smooth as the fully automatic transfer of results to the process control system so that a quick response is possible.

Potential dangers for the entire system can be caused by incorrect measurement results. In order to minimize the risk, a detector is used to notify the system of the presence of sample in the vessel. The testing of the initial potential of the analysis or titration curves / color development in photometric measurements are diagnostic data that are continuously recorded and interpreted. Results can be verified by reference analysis or their plausibility can be clarified using standard and check solutions.

Detect errors before they arise

The risk assessment procedures that are carried out in the context of a SIL classification for process engineering plants are ultimately based on mathematical calculations. However, in the 24/7 operation of a plant, random errors can never be completely excluded. Residual risk always remains. Therefore, the importance of preventive maintenance activities is growing immensely in order to avoid hardware and software failures during operation.

A regular check of the process analyzer and its diagnostic data is the basic requirement for permanent, trouble-free operation. With tailor-made maintenance and service concepts, the analyzer is supported by certified service engineers over the entire life cycle. Regular maintenance plans, application support, calibration, or performance certificates, repairs, and original spare parts as well as proper commissioning are just a few examples.

Advantages of preventive maintenance from Metrohm Process Analytics

  • Preservation of your investment
  • Minimized risk of failure
  • Reliable measurement results
  • Calculable costs
  • Original spare parts
  • Fast repair
  • Remote Support

In addition, transparent communication between the process control system and the analyzer is also relevant in the context of digitalization. The collection of performance data from the analyzer to assess the state of the control system is only one component. The continuous monitoring of relevant system components enables conclusions to be drawn about any necessary maintenance work, which ideally should be carried out at regular intervals. The question arises as to how the collected data is interpreted and how quickly it is necessary to intervene. Software care packages help to test the software according to the manufacturer’s specifications, to perform data backup and software maintenance.

«Remote support is particularly important in times when you cannot always be on site.»

In real emergency situations in which rapid error analysis is required, manufacturers can easily support the operator remotely using remote maintenance solutions. The system availability is increased, expensive failures and downtimes are avoided, and the optimal performance of the analyzer is ensured.

Read what our customers have to say!

We have supported customers even in the most unlikely of places⁠—from the production floor to the desert and even on active ships!

Post written by Dr. Kerstin Dreblow, Product Manager Wet Chemical Process Analyzers, Deutsche Metrohm Prozessanalytik (Germany).

Frequently asked questions in Karl Fischer titration – Part 2

Frequently asked questions in Karl Fischer titration – Part 2

Since I started working at Metrohm more than 15 years ago, I have received many questions about Karl Fischer titration. Some of those questions have been asked repeatedly from several people in different locations around the world. Therefore, I have chosen 20 of the most frequent questions received over the years concerning Karl Fischer equipment and arranged them into three categories: instrument preparation and handling, titration troubleshooting, and the oven technique. Part 1 covered instrument preparation and handling, and Part 2 will now focus on titration troubleshooting and the KF oven technique.

Summary of questions in the FAQ (click to go directly to each question):

Titration troubleshooting

1.  If the drift value is 0, does this mean that the titration cell is over-titrated?

A drift of zero can be a sign that the cell might be over-titrated. In combination with the mV signal (lower than end-point criteria) and the color of the working medium (darker yellow than usual), it is a clear indicator for over-titration. However, volumetric titrations sometimes exhibit a zero drift for a short time without being over-titrated. If you have a real excess of iodine in the titration cell, the result of the next determination will most likely be erroneous. Therefore, over-titration should be avoided. There are various possible reasons for over-titration, like the sample itself (e.g., oxidizing agents which generate iodine from the working medium), the electrode (coating or invisible depositions on the Pt pins/rings), the reagent, and method parameters (e.g., the titration is rate too high), to name just a few.

2.  Should I discard the Karl Fischer reagent immediately if it turns brown?

Different factors can cause over-titration, however, the reagent is not always the reason behind this issue. The indicator electrode can also be the reason for overshooting the endpoint. In this case, regular cleaning of the electrode can prevent over-titration (see also questions 7 to 9 from Part 1 in this series on cleaning).

A low stirring speed also increases the risk of over-titration, so make sure the solution is well mixed. Depending on the type of reagent, the parameters of the titration need to be adjusted. Especially if you use two-component reagents, I recommend decreasing the speed of the titrant addition to avoid over-titration. Over-titration has an influence on the result, especially if the degree of over-titration changes from one determination to the next. So over-titration should always be avoided to guarantee correct results.

3.  What is drift correction, and when should I use it?

I recommend using the drift correction in coulometric KF titration only. You can also use it in volumetric titration, but here the drift level is normally not as stable as for coulometric titrations. This can result in variations in the results. A stabilization time can reduce such an effect. However, compared to the absolute water amounts in volumetry, the influence of drift is usually negligible.

4.  My results are negative. What does a negative water content mean?

Negative values do occur if you have a high start drift and a sample with a very low water content. In this case, the value for drift correction can be higher than the absolute water content of the sample, resulting in a negative water content.

If possible, use a larger sample size to increase the amount of water added to the titration cell with the sample. Furthermore, you should try to reduce the drift value in general. Perhaps the molecular sieve or the septum need to be replaced. You can also use a stabilizing time to make sure the drift is stable before analyzing the sample.

Karl Fischer oven

5.  My samples are not soluble. What can I do?

In case the sample does not dissolve in KF reagents and additional solvents do not increase the solubility of the sample, then gas extraction or the oven technique could be the perfect solution.

The sample is weighed in a headspace vial and closed with a septum cap. Then the vial is placed in the oven and heated to a predefined temperature, leading the sample to release its water. At the same time, a double hollow needle pierces through the septum. A dry carrier gas, usually nitrogen or dried air, flows into the sample vial. Taking the water of the sample with it, the carrier gas flows into the titration cell where the water content determination takes place.

6.  Can all types of samples be analyzed with the oven method?

Many samples can be analyzed with the oven. Whether an application actually works for a sample strongly depends on the sample itself. Of course, there are samples that are not suitable for the oven method, e.g., samples that decompose before releasing the water or that release their water at higher temperatures than the maximum oven temperature.

7.  How do I find the optimal oven temperature for water extraction?

Depending on the instrument used, you can run a temperature gradient of 2 °C/min. This means it is possible to heat a sample from 50 to 250 °C within 100 minutes. The software will then display a curve of water release against temperature (see graph).

From such a curve, the optimal temperature can be determined. Different peaks may show blank, adherent water, different kinds of bound water, or even decomposition of the sample.

This example curve shows the water release of a sample as it has been heated between 130 and 200 °C. At higher temperatures, the drift decreases to a stable and low level.

Generally, you should choose a temperature after the last water release peak (where the drift returns to the base level) but approximately 20 °C below decomposition temperature. Decomposition can be recognized by increasing drift, smoke, or a color change of the sample. In this example, there are no signs of decomposition up to an oven temperature of 250 °C. Therefore, the optimal oven temperature for this sample is 230 °C (250 °C – 20 °C).

In case the instrument you use does not offer the option to run a temperature gradient, you can manually increase the temperature and measure the sample at different temperatures. In an Excel spreadsheet, you can display the curve plotting released water against temperature. If there is a plateau (i.e., a temperature range where you find reproducible water contents), you have found the optimal oven temperature.

8.  What is the highest possible water content that can be measured with a Karl Fischer oven?

Very often, the oven is used in combination with a coulometric titrator. The coulometric titration cell used in an oven system is filled with 150 mL of reagent. Theoretically, this amount of reagent allows for the determination of 1500 mg of water. However, this amount is too high to be determined in one titration and it would lead to very long titration times and negative effects on the results. We recommend that the water content of a single sample (in a vial) should not be higher than 10 mg, ideally around 1000–2000 µg water. For samples with water contents in the higher percentage range, you should consider the combination with a volumetric titrator.

9.  What is the maximum sample size that can be used with the oven? If I use too much sample, will the needle be blocked?

The standard vial for the oven method has a volume of approximately 9 mL. However, we do not recommend filling the vial completely. Do not fill more than 5–6 mL of sample in a vial. We offer the possibility to customize our oven systems, allowing you to use your own vials. Please contact your local Metrohm agency for more information on customized oven systems.

For liquid samples, we recommend using a long needle to lead the gas through the sample. Solid samples and especially samples that melt during analysis require a short needle. The tip of the needle is positioned above the sample material to avoid needle blockage.

Additionally, you should use a «relative blank value», i.e., taking only the remaining air volume into account for blank subtraction. You can find more information about the relative blank and how to calculate it in Application Note AN-K-048.

10.  What is the detection limit of the oven method, and how much sample is required to analyze a sample with 10 ppm (mg/L) water content?

We recommend having at least 50 µg of water in the sample, if analyzed with coulometry. However, if conditions are absolutely perfect (i.e., very low and stable drift plus perfect blank determination), it is possible to determine even lower water contents, down to 20 µg of absolute water. For a sample with a water content of < 10 ppm (mg/L), this would correspond to a sample size of at least 2 g.

11.  How do I verify an oven method?

For the verification of an oven system, you can use a certified water standard for oven systems. With such a standard, you can check the reproducibility and the recovery. There are a few types of standards available for different temperature ranges.

I hope this collected information helps you to answer some of your most burning KF questions. If you have further unanswered questions, do not hesitate to contact your local Metrohm distributor or check out our selection of webinars.

Automate thermal sample preparation

It’s easy with an oven sample changer from Metrohm!

Post written by Michael Margreth, Sr. Product Specialist Titration (Karl Fischer Titration) at Metrohm International Headquarters, Herisau, Switzerland.

Trace metal analysis with solid-state electrodes – Part 3

Trace metal analysis with solid-state electrodes – Part 2

In the second part of our series on «heavy metal» analysis with solid-state electrodes, the focus lies on the scTRACE Gold electrode. Gold electrodes have been used in electrochemistry for decades. However, the scTRACE Gold has a very special design. Originally developed to improve the voltammetric determination of arsenic, the electrode has also proven to be suitable for the determination of a number of other elements, such as copper, iron, lead, and even the toxic chromium(VI).

How does it work?

The working electrode is a gold micro-wire (Fig. 1), which is thinner than a human hair. This special form of electrode leads to a very short initial preparation time. Different from other gold electrodes, the scTRACE Gold is ready for use within a few minutes.

Another advantage of this electrode is that it comes with the reference and the auxiliary electrode printed on the rear side of the sensor (Fig. 2). That does not only save on costs for the two additional electrodes required in a voltammetric system, it also makes maintenance for the reference electrode obsolete.

Figure 1. Close-up view of the gold micro-wire working electrode on the scTRACE Gold.

Figure 2. Close-up view of the reference and auxiliary electrode on the rear side of the scTRACE Gold.

Applications

The high level of sensitivity and a straightforward setup makes voltammetry a valuable tool in drinking water analysis.

Availability of clean drinking water is one of the major concerns of the 21st century. Besides microbiological contaminations, such as bacteria and viruses, the presence of heavy metals in drinking water can be a health risk. The first step in providing clean water is to identify contaminants, since health-threatening concentrations of heavy metals are not visible. For many heavy metals, limit values in drinking water are specified by authorities like the U.S. Environmental Protection Agency (EPA) or the European Commission. Water quality laboratories often use ICP (inductively coupled plasma) to monitor metal concentrations in drinking water.

Voltammetry is one of the few analysis techniques which offers a comparable sensitivity. Needing only basic infrastructure and low running costs, voltammetry is a viable alternative to monitor some key elements. In the following sections, some selected application examples are shown which demonstrate the capabilities of the scTrace Gold electrode in water analysis.

Arsenic in drinking water

Arsenic gained some global notoriety when water wells were built in Bangladesh to avoid diseases caused by microbiological contaminations in the surface water. Rather than suffering from cholera or hepatitis, people were instead afflicted with chronic arsenic poisoning.

It would be somewhat careless to believe that arsenic is only a problem in less developed countries. Actually, arsenic can be found nearly everywhere in the earth’s crust. Though as Paracelsus already knew, «the concentration makes the poison».

Therefore, the crucial question is how much of this arsenic finds its way into the water table. The WHO (World Health Organization) recommends a concentration of 10 µg/L arsenic as the maximum level in water that is intended for human consumption. This figure is also the legal limit in many countries.

Want to know more about arsenic? Then download our free article: «Arsenic – The multipurpose poison».

The voltammetric determination of the limit value of 10 µg/L shows a recovery of about 92% (n = 10 determinations) with a relative standard deviation of 6.5%. With a detection limit of 1 µg/L, which is one tenth of the legal limit, voltammetry using the scTRACE Gold electrode offers a reliable and cost-effective way of monitoring the arsenic content of drinking water.

For more information, download our free application note AN-V-210: Total arsenic in mineral water – Straightforward determination by voltammetry on a gold microwire electrode.

The scTRACE Gold electrode can be used with the 884 Professional VA as well as with the 946 Portable VA Analyzer. The 884 Professional VA is designed for laboratory use. The system is extremely flexible and can be adapted to user requirements. The modular setup also allows a later extension of the instrument from manual to fully automated.

As the name says, the 946 Portable VA Analyzer is intended for mobile use. It allows for on-site determination, directly at the sample source.

Copper in surface water

Under normal circumstances, copper in drinking water is not a problem. The legal limits are comparably high, WHO recommends a maximum concentration of 2 mg/L. An example from the field illustrates where the determination of copper in water can nevertheless be advisable.

The production of distilled alcoholic beverages (e.g., gin, whiskey, brandy, schnapps) involves single or multiple distillation of the raw material, which is done in copper stills. Cleaning out the copper apparatus and draining the rinsing water to a river can contaminate the environment with copper.

Although regulatory limits in effluents are usually higher than in drinking water, the copper limits can still be exceeded if the water is not treated properly prior to discharge. Since pollution from this cleaning is not a continuous process but only occurs periodically, it is difficult to detect and even harder to confirm, especially in less accessible areas.

Here, mobile voltammetry using the scTRACE Gold with the 946 Portable VA Analyzer can make a valuable contribution to the protection of the environment due to the reliable determination of low concentrations of copper.

For a concentration of 5 µg/L, the mean recovery of 10 determinations is approximately 107%, with a relative standard deviation of 2%. Concentrations down to 0.5 µg/L copper in the water can be determined directly at the point of sampling. This allows immediate re-sampling in case of suspicious results, and can furthermore help to locate the source of the pollution. In this way, chances increase to identify the source and hold the responsible entity accountable.

For more information, download our free application note AN-V-213: Copper in drinking water – Straightforward determination by voltammetry using a gold microwire electrode.

Iron in water

According to WHO, iron does not pose a health concern in levels typically found in drinking water. In contrast, it is an essential element for human nutrition. Nevertheless, many countries specify a maximum contaminant level between 200 µg/L and 300 µg/L.

The reason is simply that higher concentrations have a negative effect on the taste of the water, and will stain laundry and sanitary appliances. 

With a detection limit of 10 µg/L, the voltammetric determination of iron offers a straightforward method for monitoring the iron concentration of the water supply. The recovery of a voltammetric determination of 20 µg/L Fe is in the range of 91% (n = 10 determinations) with a relative standard deviation of 1%.

For more information, download our free application note AN-V-216: Iron in drinking water – Straightforward determination by voltammetry using a gold microwire electrode (DHN method).

What’s next?

In part two of this series, I introduced the scTRACE Gold electrode which I will also continue to discuss in Part 3. In the next installment, I will focus on applications which are carried out after electrochemical modification of the gold micro-wire.

Post written by Barbara ZumbrägelProduct Manager VA/CVS at Metrohm International Headquarters, Herisau, Switzerland.

Making a better beer with chemistry

Making a better beer with chemistry

Lager or ale? Pale ale or stout? Specialty beer, or basic draft? This week, to celebrate the International Beer Day on Friday, August 7th, I have chosen to write about a subject near and dear to me: how to make a better beer! Like many others, at the beginning of my adult life, I enjoyed the beverage without giving much thought to the vast array of styles and how they differed, beyond the obvious visual and gustatory senses. However, as a chemist with many chemist friends, I was introduced at several points to the world of homebrewing. Eventually, I succumbed.

Back in 2014, my husband and I bought all of the accessories to brew 25 liters (~6.5 gallons) of our own beer at a time. The entire process is controlled by us, from designing a recipe and milling the grains to sanitizing and bottling the finished product. We enjoy being able to develop the exact bitterness, sweetness, mouthfeel, and alcohol content for each batch we brew.

Over the years we have become more serious about this hobby by optimizing the procedure and making various improvements to the setup – including building our own temperature-controlled fermentation fridge managed by software. However, without an automated system, we occasionally run into issues with reproducibility between batches when using the same recipe. This is an issue that every brewer can relate to, no matter the size of their operation.

Working for Metrohm since 2013 has allowed me to have access to different analytical instrumentation in order to check certain quality attributes (e.g., strike water composition, mash pH, bitterness). However, Metrohm can provide much more to those working in the brewing industry. Keep reading to discover how we have improved analysis at the largest brewery in Switzerland.

Are you looking for applications in alcoholic beverages? Check out this selection of FREE Application Notes from Metrohm:

Lagers vs. Ales

There are two primary classes of beer: lagers and ales. The major contrast between the two is the type of yeast used for the fermentation process. Lagers must be fermented at colder temperatures, which lends crisp flavors and low ester formation. However, colder processes take longer, and so fermentation steps can last for some months. Ales have a much more sweet and fruity palate of flavors and are much easier to create than lagers, as the fermentation takes place at warmer temperatures and happens at a much faster rate.

Comparison between the fermentation of lagers and ales.

Diving a bit deeper, there are several styles of beer, from light pilsners and pale ales to porters and black imperial stouts. The variety of colors and flavors depend mostly on the grains used during the mash, which is the initial process of soaking the milled grains at a specific temperature (or range) to modify the starches and sugars for the yeast to be able to digest. The strain of yeast also contributes to the final flavor, whether it is dry, fruity, or even sour. Taking good care of the yeast is one of the most important parts of creating a great tasting beer.

Brewing terminology

  • Malting: process of germinating and kilning barley to produce usable sugars in the grain
  • Milling: act of grinding the grains to increase surface area and optimize extraction of sugars
  • Mashing: releasing malt sugars by soaking the milled grains in (hot) water, providing wort
  • Wort: the solution of extracted grain sugars
  • Lautering: process of clarifying wort after mashing
  • Sparging: rinsing the used grains to extract the last amount of malt sugars
  • Boiling: clarified wort is boiled, accomplishing sterilization (hops are added in this step)
  • Cooling: wort must be cooled well below body temperature (37 °C) as quickly as possible to avoid infection
  • Pitching: prepared yeast (dry or slurry) is added to the cooled brewed wort, oxygen is introduced
  • Fermenting: the process whereby yeast consumes simple sugars and excretes ethanol and CO2 as major products

Ingredients for a proper beer

These days, beer can contain several different ingredients and still adhere to a style. Barley, oats, wheat, rye, fruit, honey, spices, hops, yeast, water, and more are all components of our contemporary beer culture. However, in Bavaria during the 1500’s, the rules were much more strict. A purity law known as the Reinheitsgebot (1516) stated that beer must only be produced with water, barley, and hops. Any other adjuncts were not allowed, which meant that other grains such as rye and wheat were forbidden to be used in the brewing process. We all know how seriously the Germans take their beer – you only need to visit the Oktoberfest once to understand!

Determination of the bitterness compounds in hops, known as «alpha acids», can be easily determined with Metrohm instrumentation. Check out our brochure for more information:

You may have noticed that yeast was not one of the few ingredients mentioned in the purity law, however it was still essential for the brewing process. The yeast was just harvested at the end of each batch and added into the next, and its propagation from the fermentation process always ensured there was enough at the end each time. Ensuring the health of the yeast is integral to fermentation and the quality of the final product. With proper nutrients, oxygen levels, stable temperatures, and a supply of simple digestible sugars, alcohol contents up to 25% (and even beyond) can be achieved with some yeast strains without distillation (through heating or freezing, as for eisbocks).

Improved quality with analytical testing

Good beers do not make themselves. For larger brewing operations, which rely on consistency in quality and flavor between large batch volumes as well as across different countries, comprehensive analytical testing is the key to success.

Metrohm is well-equipped for this task, offering many solutions for breweries large and small.

Don’t take it from me – listen to one of our customers, Jules Wyss, manager of the Quality Assurance laboratory at Feldschlösschen brewery, the largest brewery in Switzerland.

«I have decided to go with Metrohm, because they are the only ones who are up to such a job at all. They share with us their huge know-how.

I can’t think of any other supplier who would have been able to help me in the same way

Jules Wyss

Manager Quality Assurance Laboratory, Feldschlösschen Getränke AG

Previous solutions failed

For a long time, Jules determined the quality parameters in his beer samples using separate analysis systems: a titrator, HPLC system, alcohol measuring device, and a density meter. These separate measurements involved a huge amount of work: not only the analyses themselves, but also the documentation and archiving of the results all had to be handled separately. Furthermore, Jules often had to contend with unreliable results – depending on the measurement procedure, he had to analyze one sample up to three times in order to obtain an accurate result.

A tailor-made system for Feldschlösschen

Jules’ close collaboration with Metrohm has produced a system that takes care of the majority of the necessary measurements. According to Jules, the system can determine around 90% of the parameters he needs to measure. Jules’ new analysis system combines various analysis techniques: ion chromatography and titration from Metrohm as well as alcohol, density, and color measurement from another manufacturer. They are all controlled by the tiamo titration software. This means that bitterness, citric acid, pH value, alcohol content, density, and color can all be determined by executing a single method in tiamo.

Measurement of the overall water quality as well as downstream analysis of the sanitization process on the bottling line is also possible with Metrohm’s line of Process Analysis instrumentation.

Integrated analytical systems with automated capabilities allow for a «plug and play» determination of a variety of quality parameters for QA/QC analysts in the brewing industry. Sample analysis is streamlined and simplified, and throughput is increased via the automation of time-consuming preparative and data collection steps, which also reduces the chance of human error.

Something to celebrate: The Metrohm 6-pack (2018)

In 2018, Metrohm celebrated its 75 year Jubilee. At this time, I decided to combine my experience as a laboratory analyst as well as a marketing manager to brew a series of six different styles of beer for the company, as a giveaway for customers of our Metrohm Process Analytics brand, for whom I worked at the time. Each batch was brewed to contain precisely 7.5% ABV (alcohol by volume), to resonate with the 75 year anniversary. The array of ales was designed to appeal to a broad audience, featuring a stout, porter, brown ale, red ale, hefeweizen, and an India pale ale (IPA). Each style requires different actions especially during the mashing process, based on the type of grains used and the desired outcome (e.g., flavor balance, mouthfeel, alcohol content).

Bespoke bottle caps featuring the Metrohm logo.
The 6 styles of beers brewed as a special customer giveaway to celebrate the Metrohm 75 year Jubilee.

Using a Metrohm Ion Chromatograph, I analyzed my home tap water for concentrations of major cations and anions to ensure no extra salts were needed to adjust it prior to mashing. After some of the beers were prepared, I tested my colleagues at Metrohm International Headquarters in the IC department, to see if they could determine the difference between two bottles with different ingredients:

Overlaid chromatograms from IC organic acid analysis highlighting the differences between 2 styles of the Metrohm 75 year Jubilee beers.

The IC analysis of organic acids and anions showed a clear difference between the beers, allowing them to determine which sample corresponded to which style, since I did not label them prior to shipping the bottles for analysis. As the milk stout contained added lactose, this peak was very pronounced and a perfect indicator to use.

Metrohm ion chromatography, along with titration, NIRS, and other techniques, allows for reliable, comprehensive beer analysis for all.

In conclusion, I wish you a very happy International Beer Day this Friday. Hopefully this article has illuminated the various ways that beer and other alcoholic beverages can be analytically tested for quality control parameters and more  fast, easy, and reliably with Metrohm instrumentation.

For more information about the beer quality parameters measured at Feldschlösschen brewery, take a look at our article: «In the kingdom of beer The largest brewery in Switzerland gets a made-to-measure system». Cheers!

Read the full article:

«In the kingdom of beer – The largest brewery in Switzerland gets a made-to-measure system»

Post written by Dr. Alyson Lanciki, Scientific Editor (and «chief brewing officer») at Metrohm International Headquarters, Herisau, Switzerland.