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Best practice for electrodes in Karl Fischer titration

Best practice for electrodes in Karl Fischer titration

Have you ever asked yourself why you need an electrode for the endpoint detection in Karl Fischer (KF) titration? Theoretically, the endpoint of a Karl Fischer titration could be determined based on the color change of the reagent. However, if accuracy and reproducibility are important, endpoint detection with a double Pt electrode is a much better choice.

As the indicator electrode detects the endpoint, you can imagine that the results depend highly on the condition of the electrode. In coulometry, an additional electrode (generator electrode) is used to generate the iodine needed for the titration. Both electrode types (i.e. indicator and generator electrode) need to be kept in good shape to guarantee the correct results. It goes without saying that cleaning, storage, maintenance, and checks of the KF electrodes are important factors for success. This blog post takes a closer look at these topics.

Did you catch our series about frequently asked questions in Karl Fischer titration? Find them here!

Cleaning

Indicator electrode

Double  Pt-wire or double Pt-ring electrodes can be easily cleaned with an abrasive cleaning agent like aluminum oxide powder or toothpaste. After cleaning, rinse the electrode well with water and let it dry before mounting it in a titration cell. Check out our video below for more tips and tricks about the proper cleaning procedure for Karl Fischer titration indicator electrodes.

Take special care not to bend the Pt pins of the double Pt-wire electrode. Bending the pins can lead to tiny cracks in the glass body of the electrode. Over time, reagent can flow into the electrode and lead to corrosion (short circuit). If this happens, the electrode is beyond repair and needs replacement. Alternatively, a double Pt-ring electrode can be used instead. Problems with bent pins are then a thing of the past.
Generator electrode
Without diaphragm
Rinse generator electrodes without diaphragms with water, or if the contaminant is not water soluble, then rinse with a suitable organic solvent. If the anode or the cathode of the generator electrode shows discoloration or deposits that cannot be removed with rinsing, the electrode can then be cleaned with concentrated nitric acid (65%). Be aware that nitric acid is a strong oxidizing agent and must be handled carefully according to relevant safety regulations and instructions. Remember to first mount the green protection cap on the connector to avoid corrosion caused by fumes of nitric acid. Afterwards, rinse the electrode with water and finally with methanol.
With diaphragm
To remove salt-like residues, the generator electrode with diaphragm can be rinsed with water. Oily contamination can be rinsed off with an organic solvent (e.g. hexane). Sticky residues on the diaphragm can be removed in the following way: 

  1. Mount the green protection cap on the connector of the electrode.
  2. Place the electrode in an upright position (e.g. in an Erlenmeyer flask) and add a few milliliters of concentrated nitric acid (65%) in the cathode chamber. Let the acid flow through the diaphragm.
  3. Fill the cathode chamber with water and let it flow through the diaphragm to remove the nitric acid. Repeat this step two or three times. A simple way to see whether another rinsing step is required is by performing a quick check of the pH value at the cathode using pH indication paper.
  4. Finally, fill the cathode chamber with methanol and let it flow out.

Now the generator electrode is as good as new and ready for use in a titration cell again.

Maintenance

Except for the generator electrode with diaphragm, KF electrodes are maintenance free. However, the catholyte filled in the generator electrode with diaphragm can decompose over time. To avoid any influence of the decomposition products on the results, exchange the catholyte on a regular basis according to the manufacturer’s recommendations.

Storage

Unlike pH electrodes, KF electrodes do not contain a glass membrane that could potentially dry out. Therefore, no special solution is required in which to store KF electrodes. If you use the electrodes frequently, it is recommended to keep the electrodes mounted in the titration cell and immersed in the KF reagent. Alternatively, all KF electrodes (indicator and generator electrodes) can be stored dry.

What to check for

It is recommended to check the complete titration setup instead of only the electrode(s).

Volumetry

Carry out a threefold titer determination using either a liquid or a solid water standard suitable for volumetry and calculate the mean value of the titer. Then, determine the water content of a water standard (also via triplicate determination). Make sure that you do not use the same standard as for the titer determination but use a different batch of the standard or even a completely different standard. Calculate the water content and compare it to the certified water content of the standard.

If the recovery is determined to be in the range of 97–103%, the titration system (including the electrode) is working fine. Finding values outside this range means that there is something wrong with the titration system or with the determination procedure. Results of the sample analysis would very likely also deviate from the real water content. Therefore, it is important to find the reason for values that are too high or too low. Sometimes the reason for deviations is just an air bubble in the dosing cylinder or due to an exhausted molecular sieve. However, if you do not find the reason, do not hesitate to contact your local Metrohm agency.

Coulometry

Water standards with lower water contents (0.1%) are available to properly check the health of coulometric titration systems. Carry out a water content determination in triplicate with such a standard. Calculate the recovery with the obtained results and the certified water content of the standard.

A recovery value in the range between 97–103% means that everything is fine with the system and that the electrodes work as expected. As with volumetry, in coulometry it is important to find the reason for any deviating recovery values. Make sure that you find and eliminate the problem to obtain correct results for your samples.

What you should avoid

  • Do not use solvents that contain ketones or aldehydes (e.g. denatured ethanol) to clean KF electrodes or any KF accessories.
  • Do not treat KF electrodes in an ultrasonic bath. This might destroy the electrode.
  • For drying, use a maximum temperature of 50 °C. Higher temperatures might damage the electrode.
  • Do not bend the Pt pins of the double Pt-wire electrode.

Summary

As you can see, keeping your KF electrodes in good shape is actually very simple. Regular cleaning helps to avoid erroneous results and ensures that your Karl Fischer electrodes will work for a long time.

Best practice for electrodes in titration

Treat your sensors right!
Post written by Michael Margreth, Sr. Product Specialist Titration (Karl Fischer Titration) at Metrohm International Headquarters, Herisau, Switzerland.
Unmatched flexibility in online ion analysis: The 2060 IC Process Analyzer

Unmatched flexibility in online ion analysis: The 2060 IC Process Analyzer

When discussing chemical analysis, the first thing that comes to mind is a chemist working in the laboratory analyzing a sample.

However, in the industrial process world chemical analysis is a much more complicated affair. In the metalworking industry for example, corrosion is a complex problem. The conventional approach (offline analysis systems) is costly, and a more proactive approach is needed for prevention, identification, and manufacturing of high quality metalworking products. Therefore, a more comprehensive sample monitoring and analysis approach is necessary in order to comply with such requirements.

While offline analysis systems depend upon an analyst to collect and process samples, an online analysis system allows for continuous monitoring of multiple parameters in real time without being dependent on an analyst.

Need to refresh your knowledge about the differences between online, inline, and atline analysis? Read our blog post: «We are pioneers: Metrohm Process Analytics».

The implementation of Process Analytical Technologies (PAT) provides a detailed representation in real time of the actual conditions within a process. As a complete solution provider, Metrohm Process Analytics offers the best solutions for online chemical analysis. We seek to optimize process analysis by developing flexible, modular process analyzers that allow multiple analyses of different analytes from a representative sample taken directly at the process site.

Want to learn more about PAT? Check out our article series here: «To automate or not to automate? Advantages of PAT – Part 1».

2060 IC Process Analyzer

With more than 40 years of experience with online process analysis, Metrohm Process Analytics has always been committed to innovation. In 2001, the first modular IC system was developed at Metrohm and it was a success. In the past several years Metrohm Process Analytics focused on implementing more modular flexibility in their products, which resulted in the introduction of the next generation of Process Ion Chromatographs: the 2060 IC Process Analyzer (Figure 1) in 2019. It is built using two 930 Compact IC Flex systems and is in full synergy with the Metrohm process analyzer portfolio (such as the 2060 Process Analyzer).

Figure 1. The 2060 IC Process Analyzer from Metrohm Process Analytics. Pictured here is the touchscreen human interface, the analytical wet part (featuring additional sample preparation modules – top inlay, and the integrated IC – bottom inlay), and a reagent cabinet.

For more background behind the development of IC solutions for the process world, check out our previous blog posts featuring the past of the 2060 IC Process Analyzer:

Using the 2060 platform, modularity is taken to the next step. Configurations of up to four wet part cabinets allow numerous combinations of multiple analysis modules for multiparameter measurements on multiple process streams, making this analyzer unequal to any other on the market.

This modular architecture gives the additional possibility to place separate cabinets in different locations around a production site for a wide angle view of the process. For example, the 2060 IC Process Analyzer can be set up at different locations to prevent corrosion on the water steam cycles in fossil and nuclear power plants.

The 2060 IC Process Analyzer is managed using flexible software enabling straightforward efficient control and programming options. With multiple types of detectors available from Metrohm, high precision analysis of a wide spectrum of analytes is possible in parallel.

The inclusion of an optional (pressureless) ultrapure water system for autonomous operation and reliable trace analysis also benefits users by providing continuous eluent production possibilities for unattended operation (Figure 2).

Finally, the well-known Metrohm Inline Sample Preparation (MISP) techniques are an added bonus for process engineers for repeatable, fully automated preparation of challenging sample matrices.

Figure 2. Continuous eluent production integrated in the 2060 IC Process Analyzer.

Top applications

The collection of samples and process data, including corrosion prevention and control indicators, is critical for efficient plant management in many industries. In order to prevent unscheduled plant shutdowns, accidents, and damage to company assets, process engineers rely on their colleagues in the lab to pinpoint corrosion problems. One of the most effective ways to bridge laboratory analyses to the process environment is to employ real-time analysis monitoring.

Figure 3. Product and process optimization differences between offline, atline, online, and inline analysis.

Optimal online corrosion management

Be it quantifying the harmful corrosive ions (e.g., chlorides, sulfates, or organic acids), measuring corrosion inhibitors (e.g., ammonia, amines, and film-forming amines), or detecting corrosion products, the 2060 IC Process Analyzer is the ideal solution for 24/7 unattended analysis.

In a nuclear power plant, this analyzer can measure a number of analytes including inorganic anions, organic cations, and aliphatic amines to ensure a thorough understanding of corrosive indications without needing multiple instruments.

Figure 4. Water sample from the primary circuit of a pressurized water reactor containing 2 g/L H3BO3 and 3.3 mg/L LiOH spiked with 2 μg/L anions (preconcentration volume: 2000 μL).
Figure 5. Simulated sample from the primary circuit of a pressurized water reactor containing 2 g/L H3BO3 and 3.3 mg/L LiOH spiked with 2 μg/L nickel, zinc, calcium, and magnesium (preconcentration volume: 1000 μL).

Providing quick, reliable results, this system gives valuable insight into the status of corrosion processes within a plant by continuous comparison of results with control values. By correlating the results with specific events, effective corrective action can quickly be undertaken to prevent or minimize plant downtime.

For more information about the determination of anions and cations in the primary circuit of nuclear power plants with the 2060 IC Process Analyzer, download our free Application Notes below.

Online drinking water analysis

In drinking water plants and beverage bottling companies, determination of disinfection byproducts (DBPs) like bromate is crucial due to their carcinogenic properties. The carcinogen bromate (BrO3) has a recommended concentration limit of 10 μg/L of in drinking water set by the World Health Organization.

Nowadays, ion chromatography has been proven to be the best routine analysis method for water analysis, due to its possibility of automated sample preparation, various separation mechanisms, and different types of detectors. Some of the analytical standards that support this include: EPA 300.1EPA 321.8, ASTM D6581, ISO 11206, and ISO 15061.

The 2060 IC Process Analyzer can monitor trace levels of bromate in drinking water online, meaning higher throughput, less time spent performing manual laboratory tests, and better quality drinking water.

Figure 6. Drinking water sample, spiked with 10 μg/L each of chlorite, bromate, chlorate, 40 μg/L each of nitrate, bromide, 100 μg/L phosphate, and 500 μg/L dichloroacetate.
Figure 7. Analysis of a mineral water sample spiked with 0.5 μg/L bromate.

To learn more about the online analysis of bromate in drinking water with the 2060 IC Process Analyzer, download our free Application Note.

Monitoring aerosols and gases in air

Approximately 92% of the world population lives in places where the World Health Organization air quality guideline levels are not met. Air pollution can exacerbate preexisting health conditions and shorten lifespans. It has even been suggested as a link to infertility causes. Hence, understanding the impact of air pollution and air constituents on the environment and our wellbeing is of great significance.

Air pollution is caused not only by gaseous compounds, but also by aerosols and particulate matter (PM). These extremely fine particles enter and damage the lungs; from them, ultrafine particles can spread across the body through the blood cells and cause symptoms of inflammation. While these risks are being debated and researched actively around the world, it is still not known which compounds actually cause harm.

As a result, there is a great need for more specific data on long-term measurements. Fast analytical methods and real-time measurements of concentrations of chemical compounds in ambient air are important and should make it possible to better understand the circumstances and effects.

For optimal air quality monitoring, the gas and aerosol composition of the surrounding air has to be analyzed practically simultaneously as well as continuously, which is possible via inline analysis with ion chromatography.

Metrohm Process Analytics offers the 2060 MARGA (Monitor for AeRosols and Gases in ambient Air) which thanks to its dual-channel ion chromatograph, can automatically analyze the ions from the collected gas and aerosol samples.

If you want to learn more background behind the development of the 2060 MARGA, check out our previous blog post: History of Metrohm IC – Part 5.

For a full list of free downloadable 2060 IC applications, visit our website and check out the Metrohm Application Finder!

Free Application Notes

For the 2060 IC Process Analyzer

Post written by Andrea Ferreira, Technical Writer at Metrohm Applikon, Schiedam, The Netherlands.

«Analyze This»: 2020 in review

«Analyze This»: 2020 in review

I wanted to end 2020 by thanking all of you for making «Analyze This» – the Metrohm blog for chemists such a success! For our 60th blog post, I’d like to look back and focus on the wealth of interesting topics we have published this year. There is truly something for everyone: it doesn’t matter whether your lab focuses on titration or spectroscopic techniques, or analyzes water samples or illicit substances – we’ve got you covered! If you’re looking to answer your most burning chemical analysis questions, we have FAQs and other series full of advice from the experts. Or if you’re just in the mood to learn something new in a few minutes, there are several posts about the chemical world to discover.

We love to hear back from you as well. Leaving comments on your favorite blog posts or contacting us through social media are great ways to voice your opinion—we at Metrohm are here for you!

Finally, I wish you and your families a safe, restful holiday season. «Analyze This» will return on January 11, 2021, so subscribe if you haven’t already done so, and bookmark this page for an overview of all of our articles grouped by topic!

Stay healthy, and stay curious.

Best wishes,

Dr. Alyson Lanciki, Scientific Editor, Metrohm AG

Quickly jump directly to any section by clicking a topic:

Customer Stories

We are curious by nature, and enjoy hearing about the variety of projects where our products are being used! For some examples of interesting situations where Metrohm analytical equipment is utilized, read on.

From underwater archaeological research to orbiting Earth on the International Space Station, Metrohm is there! We assist on all types of projects, like brewing top quality beers and even growing antibiotic-free shrimp – right here in Switzerland.

Interested in being featured? Contact your local Metrohm dealer for details!

Titration

Metrohm is the global market leader in analytical instruments for titration. Who else is better then to advise you in this area? Our experts are eager to share their knowledge with you, and show this with the abundance of topics they have contributed this year to our blog.

For more in-depth information about obtaining the most accurate pH measurements, take a look at our FAQ about pH calibration or read about avoiding the most common mistakes in pH measurement. You may pick up a few tips!

Choose the best electrode for your needs and keep it in top condition with our best practices, and then learn how to standardize titrant properly. Better understand what to consider during back-titration, check out thermometric titration and its advantages and applications, or read about the most common challenges and how to overcome them when carrying out complexometric titrations

If you are interested in improving your conductivity measurements, measuring dissolved oxygen, or the determination of oxidation in edible fats and oils, check out these blog posts and download our free Application Notes and White Papers!

Finally, this article about comprehensive water analysis with a combination of titration and ion chromatography explains the many benefits for laboratories with large sample loads. The history behind the TitrIC analysis system used for these studies can be found in a separate blog post.

Karl Fischer Titration

Metrohm and Karl Fischer titration: a long history of success. Looking back on more than half a century of experience in KFT, Metrohm has shaped what coulometric and volumetric water analysis are today.

Aside from the other titration blog posts, our experts have also written a 2-part series including 20 of the most frequently asked questions for KFT arranged into three categories: instrument preparation and handling, titration troubleshooting, and the oven technique. Our article about how to properly standardize Karl Fischer titrant will take you step by step through the process to obtain correct results.

For more specific questions, read about the oven method for sample preparation, or which is the best technique to choose when measuring moisture in certain situations: Karl Fischer titration, near-infrared spectroscopy, or both?

Ion Chromatography (IC)

Ion chromatography has been a part of the Metrohm portfolio since the late 1980s. From routine IC analysis to research and development, and from stand-alone analyzers to fully automated systems, Metrohm has provided IC solutions for all situations. If you’re curious about the backstory of R&D, check out the ongoing series about the history of IC at Metrohm.

Metrohm IC user sitting at a laboratory bench.

Common questions for users are answered in blog posts about IC column tips and tricks and Metrohm inline ultrafiltration. Clear calculations showing how to increase productivity and profitability in environmental analysis with IC perfectly complement our article about comprehensive water analysis using IC and titration together for faster sample throughput.

On the topic of foods and beverages, you can find out how to determine total sulfite faster and easier than ever, measure herbicides in drinking water, or even learn how Metrohm IC is used in Switzerland to grow shrimp!

Near-Infrared Spectroscopy (NIRS)

Metrohm NIRS analyzers for the lab and for process analysis enable you to perform routine analysis quickly and with confidence – without requiring sample preparation or additional reagents and yielding results in less than a minute. Combining visible (Vis) and near-infrared (NIR) spectroscopy, these analyzers are capable of performing qualitative analysis of various materials and quantitative analysis of a number of physical and chemical parameters in one run.

Our experts have written all about the benefits of NIR spectroscopy in a 4-part series, which includes an explanation of the advantages of NIRS over conventional wet chemical analysis methods, differences between NIR and IR spectroscopy, how to implement NIRS in your laboratory workflow, and examples of how pre-calibrations make implementation even quicker.

A comparison between NIRS and the Karl Fischer titration method for moisture analysis is made in a dedicated article.

A 2-part FAQ about NIRS has also been written in a collaboration between our laboratory and process analysis colleagues, covering all kinds of questions related to both worlds.

Raman Spectroscopy

This latest addition to the Metrohm family expands the Metrohm portfolio to include novel, portable instruments for materials identification and verification. We offer both Metrohm Raman as well as B&W Tek products to cover a variety of needs and requirements.

Here you can find out some of the history of Raman spectroscopy including the origin story behind Mira, the handheld Raman instrument from Metrohm Raman. For a real-world situation involving methamphetamine identification by law enforcement and first responders, read about Mira DS in action – detecting drugs safely in the field.

Mira - handheld Raman keeping you safe in hazardous situations.

Are you looking for an easier way to detect food fraud? Our article about Misa describes its detection capabilities and provides several free Application Notes for download.

Process Analytics

We cater to both: the laboratory and the production floor. The techniques and methods for laboratory analysis are also available for automated in-process analysis with the Metrohm Process Analytics brand of industrial process analyzers.

Learn about how Metrohm became pioneers in the process world—developing the world’s first online wet chemistry process analyzer, and find out how Metrohm’s modular IC expertise has been used to push the limits in the industrial process optimization.

Additionally, a 2-part FAQ has been written about near-infrared spectroscopy by both laboratory and process analysis experts, which is helpful when starting out or even if you’re an advanced user.

Finally, we offer a 3-part series about the advantages of process analytical technology (PAT) covering the topics of process automation advantages, digital networking of production plants, and error and risk minimization in process analysis.

Voltammetry (VA)

Voltammetry is an electrochemical method for the determination of trace and ultratrace concentrations of heavy metals and other electrochemically active substances. Both benchtop and portable options are available with a variety of electrodes to choose from, allowing analysis in any situation.

A 5-part series about solid-state electrodes covers a range of new sensors suitable for the determination of «heavy metals» using voltammetric methods. This series offers information and example applications for the Bi drop electrode, scTrace Gold electrode (as well as a modified version), screen-printed electrodes, and the glassy carbon rotating disc electrode.

Come underwater with Metrohm and Hublot in our blog post as they try to find the missing pieces of the ancient Antikythera Mechanism in Greece with voltammetry.

If you’d like to learn about the combination of voltammetry with ion chromatography and the expanded application capabilities, take a look at our article about combined analysis techniques.

Electrochemistry (EC)

Electrochemistry plays an important role in groundbreaking technologies such as battery research, fuel cells, and photovoltaics. Metrohm’s electrochemistry portfolio covers everything from potentiostats/galvanostats to accessories and software.

Our two subsidiaries specializing in electrochemistry, Metrohm Autolab (Utrecht, Netherlands) and Metrohm DropSens (Asturias, Spain) develop and produce a comprehensive portfolio of electrochemistry equipment.

This year, the COVID-19 pandemic has been at the top of the news, and with it came the discussion of testing – how reliable or accurate was the data? In our blog post about virus detection with screen-printed electrodes, we explain the differences between different testing methods and their drawbacks, the many benefits of electrochemical testing methods, and provide a free informative White Paper for interested laboratories involved in this research.

Our electrochemistry instruments have also gone to the International Space Station as part of a research project to more efficiently recycle water on board spacecraft for long-term missions.

The History of…

Stories inspire people, illuminating the origins of theories, concepts, and technologies that we may have become to take for granted. Metrohm aims to inspire chemists—young and old—to be the best and never stop learning. Here, you can find our blog posts that tell the stories behind the scenes, including the Metrohm founder Bertold Suhner.

Bertold Suhner, founder of Metrohm.

For more history behind the research and development behind Metrohm products, take a look at our series about the history of IC at Metrohm, or read about how Mira became mobile. If you are more interested in process analysis, then check out the story about the world’s first process analyzer, built by Metrohm Process Analytics.

Need something lighter? Then the 4-part history of chemistry series may be just what you’re looking for.

Specialty Topics

Some articles do not fit neatly into the same groups as the rest, but are nonetheless filled with informative content! Here you can find an overview of Metrohm’s free webinars, grouped by measurement technique.

If you work in a regulated industry such as pharmaceutical manufacturing or food and beverage production, don’t miss our introduction to Analytical Instrument Qualification and what it can mean for consumer safety!

Industry-focused

Finally, if you are more interested in reading articles related to the industry you work in, here are some compilations of our blog posts in various areas including pharmaceutical, illicit substances, food and beverages, and of course water analysis. More applications and information can be found on our website.

Food and beverages
All of these products can be measured for total sulfite content.

Oxidation stability is an estimate of how quickly a fat or oil will become rancid. It is a standard parameter of quality control in the production of oils and fats in the food industry or for the incoming goods inspection in processing facilities. To learn more about how to determine if your edible oils are rancid, read our blog post.

Determining total sulfite in foods and beverages has never been faster or easier than with our IC method. Read on about how to perform this notoriously frustrating analysis and get more details in our free LC/GC The Column article available for download within.

Measuring the true sodium content in foodstuff directly and inexpensively is possible using thermometric titration, which is discussed in more detail here. To find out the best way to determine moisture content in foods, our experts have written a blog post about the differences between Karl Fischer titration and near-infrared spectroscopy methods.

To determine if foods, beverages, spices, and more are adulterated, you no longer have to wait for the lab. With Misa, it is possible to measure a variety of illicit substances in complex matrices within minutes, even on the go.

All of these products can be measured for total sulfite content.

Making high quality products is a subject we are passionate about. This article discusses improving beer brewing practices and focuses on the tailor-made system built for Feldschlösschen, Switzerland’s largest brewer.

Pharmaceutical / healthcare

Like the food sector, pharmaceutical manufacturing is a very tightly regulated industry. Consumer health is on the line if quality drops.

Ensuring that the analytical instruments used in the production processes are professionally qualified is a must, especially when auditors come knocking. Find out more about this step in our blog post about Analytical Instrument Qualification (AIQ).

Moisture content in the excipients, active ingredients, and in the final product is imperative to measure. This can be accomplished with different analytical methods, which we compare and contrast for you here.

The topic of virus detection has been on the minds of everyone this year. In this blog post, we discuss virus detection based on screen-printed electrodes, which are a more cost-effective and customizable option compared to other conventional techniques.

Water analysis

Water is our business. From trace analysis up to high concentration determinations, Metrohm has you covered with a variety of analytical measurement techniques and methods developed by the experts.

Learn how to increase productivity and profitability in environmental analysis laboratories with IC with a real life example and cost calculations, or read about how one of our customers in Switzerland uses automated Metrohm IC to monitor the water quality in shrimp breeding pools.

If heavy metal analysis is what you are interested in, then you may find our 5-part series about trace analysis with solid-state electrodes very handy.

Unwanted substances may find their way into our water supply through agricultural practices. Find out an easier way to determine herbicides in drinking water here!

Water is arguably one of the most important ingredients in the brewing process. Determination of major anions and cations along with other parameters such as alkalinity are described in our blog post celebrating International Beer Day.

All of these products can be measured for total sulfite content.
Illicit / harmful substances

When you are unsure if your expensive spices are real or just a colored powder, if your dairy products have been adulterated with melamine, or fruits and vegetables were sprayed with illegal pesticides, it’s time to test for food fraud. Read our blog post about simple, fast determination of illicit substances in foods and beverages for more information.

Detection of drugs, explosives, and other illegal substances can be performed safely by law enforcement officers and first responders without the need for a lab or chemicals with Mira DS. Here you can read about a real life training to identify a methamphetamine laboratory.

Drinking water regulations are put in place by authorities out of concern for our health. Herbicides are important to measure in our drinking water as they have been found to be carcinogenic in many instances.

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

Electrochemistry in orbit

Electrochemistry in orbit

For over twenty years now, there has been continuous human occupation off our planet.

The International Space Station (ISS), launched in 1998, is a modular satellite in low orbit around the Earth, which is visible even with the naked eye.

Since November 2, 2000, the ISS has had a constantly revolving crew from a variety of nations, working on projects to further push the boundaries of our knowledge. Aside from their important scientific duties, these astronauts must live their daily lives like us – exercising, relaxing, cleaning, and sleeping – albeit in microgravity.

The International Space Station celebrated 20 years of constant habitation in November, 2020.

In October, an Antares rocket carrying a Cygnus resupply ship was launched by NASA at Johnson Space Center. This cargo ship carried an experimental system on board used to study the oxidation of ammonia under microgravity conditions to convert urine into water on the ISS.

Improving this waste management system has far-reaching repercussions for longer exploratory missions where the weight of the payload must be optimized with the amount of water needed (which is heavy) to sustain life during the trip. Given the limited resources aboard a spaceship, the recovery of water from all processes is of great importance.

Future missions which may benefit from this study include trips to the moon (Artemis) and eventually to Mars (Orion).

This system uses Metrohm DropSens screen-printed electrodes (SPEs). The novel nanomaterial coating of the electrodes was developed by researchers at the University of Alicante in Spain in collaboration with the University of Puerto Rico. In this article, we would like to introduce the people behind the project and elaborate on the research they are doing in space with Metrohm products.

Meet the researchers

Dr. José Solla Gullón (Ph.D. 2003, Chemistry)

Dr. José Solla Gullón in his laboratory at the University of Alicante, with Metrohm DropSens and Metrohm Autolab products on the bench.

I am currently a Distinguished Researcher at the Institute of Electrochemistry of the University of Alicante, Spain. My research mainly focuses on the synthesis, characterization and electrochemical properties of different types of nanoparticles with well-defined size, composition, shape, and surface structure. My overall publication record includes about 175 publications (h-index 53). I have also given more than 250 contributions in international and national meetings.

Ms. Camila Morales Navas

Camila Morales Navas holding the Nanoracks 2U, where the electrochemical equipment is kept inside.

I am a senior graduate student in the Department of Chemistry at University of Puerto Rico (UPR). I am working on a research project in collaboration with NASA, titled «Elucidating the Ammonia Electrochemical Oxidation Mechanism via Electrochemical Techniques at the ISS», or «Ammonia Electrooxidation Lab at the ISS (AELISS)» for short. The purpose of this project is to improve the water processing system and to identify new technology for long-term missions in space.

The project is attributed to NASA-ESPCoR, University of Puerto Rico, University of Alicante, NuVant Systems, and Nanoracks, with support from Metrohm DropSens.

Read more about the project on the NASA website:

The AELISS project

For a brief overview by Camila and her graduate advisor, have a look at the video provided below by NASA:

Here, you can see the Metrohm DropSens instruments used for this study: the screen-printed carbon electrode (SPCE8X110) and its corresponding flow-cell (FLWCL8X1C).

The Metrohm DropSens 8X110 carbon SPE (left) and the FLWCL8X1C flow-cell (right).
Instrumentation setup for the AELISS project which was launched to the ISS in October, 2020.

How did the AELISS project begin?

About five years ago, the groups from the University of Alicante and the University of Puerto Rico (UPR) began working together on microgravity experiments which led them to collaborate again for this project, which now resides on the ISS.

The electrochemical oxidation of ammonia using platinum as a catalyst is a well-established reaction, first published almost two decades ago by José’s group. The ammonia is extremely sensitive to the surface structure of platinum. However, this is well-known on earth. How does this reaction process behave in a microgravity environment? The groups sought to determine this by performing experiments in the US using a special airplane which mimics weightlessness for brief periods by flying in a parabolic motion.

SPE modification process: droplets of platinum nanoparticle ink provided by the University of Alicante deposited on the carbon SPEs. Platinum acts as a catalyst for the oxidation reaction. Click image to enlarge.

At first, this was purely for research, but later Camila’s group in Puerto Rico thought more about its potential use in space. Urea from urine is converted to ammonia, which then goes through the electrochemical oxidation process, resulting in N2 gas, water, and energy. Perhaps it was possible to use this technology to improve the onboard water recovery and recycling system in the ISS and other spaceships?

Because the UPR group often writes research proposals that are funded by NASA, they are quite knowledgeable in this area regarding the project requirements, as well as what materials are allowed on board a mission. The UPR group has been working in conjunction with NASA for about 20 years.

Unassembled equipment: plastic protector frame (grey), Metrohm DropSens FLWCL8X1C electrochemical flow-cells with 8X110 carbon SPEs (blue/white), and Nanoracks 2U (green). Click image to enlarge.

Combining the expertise in ammonia oxidation research from José’s lab in Spain with the knowledge of Camila’s group in Puerto Rico about NASA’s engineering and safety requirements made the construction and realization of the complex AELISS project possible. However, launching something to the ISS isn’t without its issues…

Has the COVID-19 pandemic had a significant effect on the research? 

Camila Morales Navas assembling the AELISS equipment in the UPR laboratory. Click image to enlarge.

Aside from the usual problems and delays that can pop up during collaborative research projects, the introduction of a global pandemic at the last stages did not help the situation. The COVID-19 pandemic affected the timeline of the AELISS project, especially when it came to traveling and working within the extremely regulated environment of NASA. Additionally, Puerto Rico had already dealt with several large earthquakes and hurricanes in this period.

Keeping each other on track became difficult at times, particularly when Camila had to bring the entire setup back home to finish the engineering. In June, she was able to return to the laboratory and complete the project. However, the stressful part was not yet over because there was still a flight to NASA in the US, and with that the ever present threat of COVID-19 infection during travel.

One positive test result would mean a denial of entry – there can be no chance of infecting the ISS crew.

Ultimately, everything went to plan before and during the launch, and the instrumentation was sent to the International Space Station in October along with other precious cargo for the astronauts. Now that this part of the puzzle is finished, the rest of the work begins…

How will AELISS differ from similar experiments on Earth?

The final goal of this research is to determine how gravity affects the oxidation of ammonia, and also to test out different catalysts for the reaction in microgravity. While several other parameters can be adjusted in the lab such as pH, nanoparticle shape, and more – gravity is a universal constraint we cannot avoid. On Earth, we are only able to mimic the effects of microgravity for a few seconds with freefall. The previous collaboration between the groups in this project also involved performing experiments on special flights that allowed weightless conditions for less than 15 seconds at a time. This is certainly not enough time to draw long-term conclusions, and hence the push to launch the project into orbit. Only then can a true comparison be made, and conclusions drawn about the effects of gravity and the future applicability of this technology.

Dr. José Solla Gullón shown in his lab at the University of Alicante depositing Pt nanocubes on the 8X110 substrates which are used in the FLWCL8X1C electrochemical cell. Click image to enlarge.

One of the major concerns regarding this project is to achieve the most efficient conversion of waste urine into usable water for long-term space missions. Here, water recycling is a critical point. Also, it is important to note that the product of the oxidation of ammonia is nitrogen gas, but the behavior of gases is not the same on Earth as in space. Understanding how the N2 bubbles behave in the absence of gravity is a critical step to study.

Camila’s doctoral research project aims to answer these questions and more, using the realistic conditions of space rather than short periods of weightlessness in flight. So how did the researchers come to use Metrohm products?

There’s Something About Metrohm

So, why choose Metrohm over other providers? I asked José and Camila just what it was that drew them to our products.

«In my case, I have been working with Metrohm DropSens for many, many years. We have a very good collaboration, not only in the in the case of the nanomaterials, but also in the electrochemical cells, and the use of the screen-printed electrodes for electroanalysis. So, we have a very long history together

Dr. José Solla Gullón

Distinguished Researcher at the Institute of Electrochemistry, University of Alicante

Additionally, José mentioned that it was the fact that the electrochemical cells from Metrohm DropSens were very small, perfectly fitting into their conceptual system, which was another critical point. In fact, only cosmetic changes were needed to the products to be used in this project – all of the used materials were already approved for use by NASA..

For Camila, this was her first time using these products, and she found their out-of-the-box usage incredibly helpful.

«This was my first experience since José suggested it. And I trust them because they’re the people that really know about this subject

Camila Morales Navas

Senior graduate student in the Department of Chemistry, University of Puerto Rico

In the past, José has asked Metrohm DropSens several times to custom design SPEs for his research needs, and has always found them responsive and agreeable.

«I know that I can send an email and in two hours, I will have some response. This is wonderful for me. They are always open to new solutions

Dr. José Solla Gullón

Distinguished Researcher at the Institute of Electrochemistry, University of Alicante

We wish the very best to the research groups behind the ambitious AELISS project at the University of Puerto Rico and the University of Alicante. We at Metrohm are proud that our products can contribute to space exploration.

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

Special thanks go to Dr. José Solla Gullón and Ms. Camila Morales Navas for their important research and taking time to contribute to this article.

Trace metal analysis with solid-state electrodes – Part 5

Trace metal analysis with solid-state electrodes – Part 5

In the last part of our series of articles about trace metal analysis using solid-state electrodes, we will have a look at the glassy carbon rotating disc electrode (GC RDE) and its application possibilities.

Did you read the other parts in this series? Find them here!

The Glassy Carbon Rotating Disc Electrode

A rotating disc electrode (RDE) consists of two parts: the electrode tip which is made available in different materials, and a driving axle. The electrode tip is simply screwed onto the axle (Figure 1) to assemble the complete working electrode.

Figure 1. The two parts which make up the RDE. Left: driving axle for RDE. Right: glassy carbon electrode tip, with shaft made of glass.

Glassy carbon (GC) has a long history as solid electrode material for trace metal analysis. In general, GC is carbon with an amorphous structure which is similar to glass or ceramics, but different from graphite or diamond which both have a crystalline structure.

Aside from properties including a high temperature stability and a hardness similar to quartz, glassy carbon is very chemically inert and has a low electrical resistance, making it a versatile electrode material.

In the Metrohm GC electrode tip (Figure 1), the glassy carbon rod is fused within a glass shaft—another inert material. This design creates an electrode tip that is inert against most chemicals and solvents and guarantees measurements with excellent reproducibility due to the seamless intersection between the electrode material and glass shaft.

Modification with a metal film

For trace metal applications, the GC electrode is modified with a metal film, usually mercury or bismuth. The film is plated ex-situ from an acid plating solution which contains about 20 mg/L Hg2+ or Bi3+. Such a solution can easily be prepared from commercially available metal standard solutions and can be used for the plating of several films.

Once the film is deposited on the glassy carbon electrode, multiple determinations can be carried out with the same film. When the performance deteriorates, the exhausted film is simply wiped off and a fresh film is plated. Since only the renewable film is affected by aging processes, the GC electrode itself can be used for a very long time.

Applications using glassy carbon electrodes exhibit excellent reproducibility and stability in combination with very low detection limits.

Figure 2. Glassy carbon rotating disc electrode in a 884 Professional VA instrument from Metrohm.

Applications

Cadmium and lead determinations

The risk of cadmium and lead poisoning from drinking water and the significance of the determination of these two elements has already been discussed in previous posts in this series. To monitor the guideline values of 3 µg/L for cadmium and 10 µg/L for lead, recommended by the WHO (World Health Organization), a detection limit of β(Cd) = 0.3 µg/L and β(Pb) = 1 µg/L would be sufficient.

With the glassy carbon electrode the determination is far more sensitive, featuring a ten-fold improvement on the limit of detection of β(Cd) = 0.02 µg/L and β(Pb) = 0.05 µg/L with a deposition time of 30 s. This limit can be lowered even more with an increased deposition time.

For this extremely sensitive determination, a mercury film is plated on the glassy carbon electrode. The determination of cadmium and lead is carried out by anodic stripping voltammetry (ASV).

To learn more about this application, please check our website.

Free Application Note download: AN-V-225 Cadmium and lead in drinking water – Simultaneous determination on a mercury film modified glassy carbon electrode.

The very low detection limit makes this application especially interesting when it is not only required to monitor limit values but to actually detect concentrations in the ppt (parts per trillion, ng/L) range, e.g. in environmental analysis such as for seawater research.

Nickel and cobalt measurements

Another application with very low detection limits using the GC electrode is the determination of nickel and cobalt. This electrode allows the detection of concentrations down to β(Ni) = 0.05 µg/L and β(Co) = 0.03 µg/L. For this application, the electrode is modified with a bismuth film. The determination of nickel and cobalt is carried out by adsorptive stripping voltammetry (AdSV) using the complexing agent DMG (dimethylglyoxime).

Figure 3. Determination of β(Ni) = 0.34 µg/L and β(Co) < LOD in tap water (30 s deposition time) using the GC RDE.

For decades, this method was successfully executed with the mercury drop electrode. The use of a bismuth film on a glassy carbon electrode offers a non-toxic alternative with a similar sensitivity as the established method. Besides the high sensitivity, this application also shows excellent repeatability.

20 consecutive determinations of β(Ni) = 0.5 µg/L and β(Co) = 0.5 µg/L, carried out on the same bismuth film, showed an average recovery of 105% for nickel, with a relative standard deviation (RSD) of 2.0%. The recovery for cobalt was 112% with a RSD of 3.3%. This makes this method a viable tool in environmental analysis when natural background concentrations, which are often in the ppt (ng/L) range, should be investigated.

For further details about this application, please refer to Application Note AN-V-224: Nickel and cobalt in drinking water – Simultaneous determination in low ng/L range on the GC RDE modified with a bismuth film.

Chromium(VI) monitoring

Legal limits for chromium are relatively high. For example, the guideline value of the World Health Organization (WHO) is 50 µg/L for drinking water. These values usually refer to the total chromium concentration, but there are significant differences in toxicity between Cr(III) and Cr(VI). Even miniscule doses of Cr(VI) are toxic as well as carcinogenic.

Since the beginning of this century, there have been ongoing discussions in the scientific community about whether an additional limit value only for Cr(VI) is required, and what this value should be.

Measuring techniques are needed which allow the determination of Cr(VI) in the ng/L range. Using the glassy carbon electrode modified with a mercury film it is possible to detect Cr(VI) concentrations down to 0.05 µg/L. Cr(VI) is determined by adsorptive stripping voltammetry (AdSV) with DTPA (diethylenetriaminepentaacetic acid) as complexing agent. The recovery of a concentration of β(Cr(VI)) = 0.1 µg/L is 111% with a relative standard deviation of 4.4% (triplicate determination).

If you are interested to learn more, download our free Application Note V-277: Chromium(VI) in drinking water – Ultra-sensitive determination on the mercury film modified glassy carbon electrode (DTPA method).

All the above-mentioned applications can be carried out manually with a 884 Professional VA system (Figure 4), but it is also possible to run small sample series with an automated setup.

Figure 4. 884 Professional VA with two 800 Dosinos for automatic addition of electrolyte and standard solution.

Summary

This was the last post in our five-part series on heavy metal analysis with solid state electrodes. If this or one of the previous posts sparked your interest in one of the applications, do not hesitate to contact your local Metrohm representative.

For a complete overview of the different applications that can be performed with the SSEs exhibited in this series, check out the table below. Click on each application note or bulletin for a free download! 

Overview: Applications with Metrohm SSEs
Element Electrode Application Document Lab Portable
Ag GC RDE Application Bulletin 207

As scTRACE Gold Application Note V-210
Application Note V-211

Bi scTRACE Gold Application Note V-218

Cd, Pb GC RDE (Hg film) Application Note V-225

Cd, Pb SPE (Hg film) Application Note V-231

Cd, Pb Bi drop Application Note V-221

Cr(VI) GC RDE (Hg film) Application Note V-227

Cr(VI) scTRACE Gold (Hg film) Application Note V-230

Cu scTRACE Gold Application Note V-213

Fe scTRACE Gold Application Note V-216

Fe Bi drop Application Note V-222

Hg scTRACE Gold Application Note V-212

Ni, Co scTRACE Gold (Bi film) Application Note V-217

Ni, Co GC RDE (Bi film) Application Note V-224

Ni, Co SPE (Bi film) Application Note V-232

Ni, Co Bi drop Application Note V-223

Pb scTRACE Gold (Ag film) Application Note V-214

Sb(III) scTRACE Gold Application Note V-229

Se(IV) scTRACE Gold Application Note V-233

Te(IV) scTRACE Gold Application Note V-234

Tl scTRACE Gold (Ag film) Application Note V-228

Zn scTRACE Gold Application Note V-215

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