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Fire and ice: discovering volcanic eruptions with ion chromatography

Fire and ice: discovering volcanic eruptions with ion chromatography

Some answers lie deep beneath the ice, waiting to be discovered.

Performing environmental chemistry research has taken me to the most remote places on Earth. In my doctoral studies, I was fortunate enough to handle samples from the South Pole and to perform my own research in Greenland, and later in Antarctica for my post-doc. What were we searching for, that took us to the middle of nowhere?

Volcanic eruptions are pretty unpredictable. Among the more active and aesthetic volcanoes with lava flows are Mount Etna in Catania (Italy), Kilauea on the large island of Hawaii (USA), and more recently Mount Fagradalsfjall in Iceland. When smaller events occur, people travel from all over to view this natural wonder. However, not all eruptions are equal…

Depending on a number of factors including the height of the eruption plume and the composition of the emissions, volcanic events can have quite a significant effect on the global climate. The Volcanic Explosivity Index (VEI) is a logarithmic scale used to measure the explosivity value of volcanic eruptions and categorize them from 0 (effusive) to 8 (mega-colossal). The largest of these events in the past century was the 1991 Pinatubo eruption in the Philippines (VEI 6, colossal). The cloud column reached high into the stratosphere, ejecting huge amounts of aerosols and gases, including sulfur dioxide (SO2) that scatter and absorb sunlight. This led to a measured global cooling effect for nearly two years after the eruption ended. Images of cloudless days at noon during this time showed a flat white hazy sky, indicative of the scattering effect of high-altitude sulfur aerosols.

Other large volcanic eruptions have led to periods of famine as well as enlightenment. It is said that the fantastic skies resulting from Krakatoa in 1883 (VEI 6, colossal) inspired Edvard Munch to paint his well-known masterpiece The Scream. If you’re familiar with Frankenstein, you can thank Mary Shelley for writing it during the wintry «year without a summer» in 1816, a result of the eruption of Mount Tambora (VEI 7, super-colossal).

Solving a mystery at the ends of the Earth

This cold period has been studied at length by several research groups and methodologies. In fact, the preceding decade had been found to be abnormally cool, however no record of another volcanic eruption was immediately apparent. Ultimately, it was pristine ice that held the clue that solved this mystery, and many others.

The sulfur dioxide emitted during volcanic eruptions is oxidized to sulfuric acid aerosols in the atmosphere, and depending on the height they reach, they can reside for days or even up to years. The deposition of volcanic sulfate on the polar ice sheets of Antarctica and Greenland preserves a record of eruptions via the continuous accumulation of snow in these areas. Therefore, records of volcanic activity can be found in polar ice cores by measuring the amount of sulfate. A fantastic way to determine sulfate, along with other a suite of major anions and cations in aqueous samples even at trace levels is with ion chromatography (IC).

The author holding a 1-meter long ice core drilled in Summit Camp, Greenland (left) and Dome Concordia, Antarctica (right).

Of course, gases can also be measured as they are trapped in the spaces between snowflakes, which are then compacted into firn and subsequently locked into the ice sheet. However, the time resolution for this is not fine enough for such volcanic measurements, nor is the volume of gas large enough to make an accurate estimate of the volcanic origin.

Gases trapped in the ice can be measured with special instrumentation and give insight into the prehistoric atmosphere.

Drilling ice cores for ion analysis is not a simple business. The logistics are staggering – getting both the field equipment and properly trained personnel to the middle of the ice sheet takes a sophisticated transportation network and cannot follow a strict schedule because Mother Nature plays by her own rules.

A complete medical checkup is necessary from top to bottom, as medical facilities can be rudimentary at best. This includes bloodwork, heart monitoring, full dental x-rays, and more (depending on your age and gender). It can take several days to evacuate a hurt or sick person to a proper hospital and therefore being in good health with an up-to-date medical record is part of being prepared for this type of remote work.

Equipment must be shipped to the site weeks or months in advance, often left at the mercy of the elements before being assembled again. Hopefully, everything works. If not, you must be very resourceful because there are no regular shipments and replacement parts are difficult to come by.

Boarding passes given to polar support staff leaving from Christchurch, New Zealand to McMurdo Station (USA) in Antarctica.

Ice cores obtained from polar areas and other remote places have been used for decades to analyze and reconstruct past events. Many considerations must be made regarding where to drill, how deep to go, and so on. The geographic location is of critical importance for several reasons including avoiding contamination from anthropogenic emissions, but also for its annual snowfall accumulation rate, proximity to volcanoes and even to other living beings (like penguin colonies, in the Antarctic).

Remote drill site based outside and upwind of Summit Camp, Greenland.

A fine resolution record of sulfate from ice cores drilled in Greenland and Antarctica has led to the discovery of previously unknown volcanic events. Ion chromatography with a dual channel system allows the simultaneous measurement of cations and anions from the same sample. When dealing with such critical samples and small volumes, this is a huge benefit for complete record keeping purposes. With the addition of automatic sample preparation like Metrohm Inline Ultrafiltration or Inline Dilution, human error is eliminated with a robust, time-saving analysis method.

Over the past two decades, the time resolution for data from ice core analysis has increased significantly. Conductivity used to be the measurement of choice to determine large volcanic events in ice cores, as it is difficult to see (unaided) the deposits of tephra from many eruptions, contrary to what you may think. The conductivity of sulfuric acid is higher than that of water, but conductivity is a sum parameter and does not disclose exactly what components are in the sample.

Tephra layers deposited by a volcanic eruption in Iceland.

Even when IC began to build traction in this space, the sample sizes did not allow researchers to determine monthly variations, but yearly approximations. This meant that any smaller sulfate peaks could have been overlooked. Researchers have tried to overcome this by matching records from ice cores around the globe to estimate the size, origin, and climatic impact of past volcanoes. Unfortunately, when the drill site is located close to active volcanism (as is the case with Greenland, downwind from Iceland), even smaller eruptions can seem to have an oversized effect.

Drilling into the ice always requires keeping track of the top and bottom ends of each meter!

The enhanced time resolution now possible with more sophisticated sample preparation (i.e. continuous flow setups for sample melting without contamination) for small volume IC injection allows for more accurate dating of volcanic eruptions without other apparent historical records.

Selected data from a drilled ice core, measured by IC. Trace analysis is necessary due to the low concentrations of ionic species deposited in remote locations. Annual layer counting was possible here, as shown with the yearly variations in several measured analytes. Grey bars represent the summer season.

Depending on the annual snowfall at the drill site and the depth of the core drilled, it can be possible to determine which month in a given year the deposition of sulfate from a volcanic eruption occurred.

This information, combined with other data (e.g., deposition length) helps pinpoint the circulation of the eruption plume and estimate the global impact. Aside from this, other data can be gained by measuring the isotopic composition of the deposited sulfate to determine the height of the eruption cloud (a more accurate method to confirm stratospheric eruptions), but that is beyond the scope of this article.

Storing hundreds of meters of ice cores during a summer research campaign in Antarctica.
Summers at Dome Concordia are not balmy, as shown in the temperature data (-54.3 °C wind chill!).

Using ion chromatography, it is possible even in the field to accurately determine the depth where specific volcanic events of interest lie in the ice. Then several ice cores can be drilled in the same location to procure a larger volume of ice to perform more detailed analyses.

My ice core research laboratory in Antarctica. Left: Metrohm IC working around the clock in the warm lab. Right: the ice core sample processing area in the cold lab (kept at -20 °C).

To solve this particular mystery, it was the combination of matching the same sulfate peak measured via IC in ice cores from both polar regions along with confirming the stratospheric nature of the eruption that led to the discovery of a previously unrecorded volcanic event in the tropics around the year 1809 C.E.

Transporting insulated ice cores back home for further research takes the cooperation of scientists, camp support staff, and the government. If flying, the entire flight must be kept cold to ensure the integrity of the ice. Any unlucky person catching a ride on a cold-deck flight must bundle up!

Cold period was extended by a second volcanic eruption

In fact, the stratospheric Tambora eruption in 1815 was already preceded by another huge climate-impacting event in the tropics just a few years before. This combination led to one of the coldest periods in the past 500 years. The data obtained by IC measurements of ice cores was instrumental in this discovery, and many more in the past few years.

Leaving the Antarctic continent can happen in a number of ways: by boat, military aircraft, or a plane. I was lucky enough to catch a first class ride on a government plane, with the added bonus of having a very interesting flight plan on screen.

High impact data

Other new volcanic eruptions have been discovered in the ice core record as the analytical technology improves. Their eruption dates can also be more accurately determined, helping to explain which of them had a climatic impact or not. This information helps to improve the accuracy of climate models, as the high altitude sulfate aerosols resulting from large eruptions reflect the sun and cause long periods of global cooling. It is for this reason that some groups have proposed a form of geoengineering where controlled amounts of sulfur gases are injected high into the atmosphere to mimic the effects of a stratospheric eruption.

In conclusion

I hope that this brief summary of a niche of environmental research with ion chromatography has piqued your interest! Maybe the inspiration of knowing that such roles exist will push other young scientists to pursue a similar career path. Chemistry education does not always have to happen indoors!

Robust ion chromatography solutions

Metrohm has what you need!

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

Analysis of prebiotics with IC-PAD: Improving AOAC 2001.02

Analysis of prebiotics with IC-PAD: Improving AOAC 2001.02

Our diet is critical for our health. In the past several years, interest has increased in food additives and dietary supplements such as prebiotics like β-galactooligosaccharides (GOSs). The determination of total GOS contents in food and supplements is essential to fulfill strict food labeling and safety requirements. The most widely used method for total GOS determination is based on enzymatic hydrolysis to break down the complex molecules into simple carbohydrates prior to their chromatographic analysis. This article outlines the advantage of using an improvement to AOAC Method 2001.02 using ion chromatography with amperometric detection (IC-PAD) and full sample automation after enzymatic hydrolysis.

What are GOSs?

GOSs are chains of galactose units with an optional glucose end. They are often naturally present in small amounts in various foods and beverages.

Initially discovered as major constituents of human breast milk (present up to 12 g/L), GOSs are added as a prebiotic supplement to infant formulas. They show bifidogenic effects, meaning they support growth and well-being of non-pathogenic gut bacteria.

GOS supplements are available either raw, or as concentrated powders or syrups, and are subsequently used by food manufacturers to enrich consumer products or sold as supplements.

GOS labeling requirements

The ongoing growth of global prebiotic and GOS markets is a result of increasing consumer awareness regarding healthy eating. Similarly, increased demand regarding food quality has led to stricter, more comprehensive rules for food labeling and safety (e.g., EU 1169/2011 and  EU 2015/2283). The determination of total GOS contents in food, supplements, or raw products is thus essential to fulfill such requirements.

Studies about GOS health effects recommend maximum doses under 30 g per day, though this is much stricter for infant formulas. Otherwise, there are no other limits regarding GOS content in food or as nutritional supplements.

AOAC 2001.02

The most widely used method to measure total GOSs in food products is the standard method AOAC 2001.02. This method is based on the extraction of GOS from a sample followed by enzymatic hydrolysis of the oligosaccharides into monosaccharides and their subsequent analyses with high performance anion exchange chromatography with pulsed amperometric detection.

Figure 1. Schematic for determination of total GOS contents using ion chromatography with pulsed amperometric detection (IC-PAD) according to AOAC 2001.02, and an optimized method from Metrohm (in green). Chromatography for anions in AOAC is referred as HPAEC (high performance anion exchange chromatography) but is simplified here to the generic term of IC.

In AOAC, chromatography for anions is referred to as HPAEC (high performance anion exchange chromatography) but here we will simplify this to the generic term of IC.

The key to AOAC 2001.02 is the comparison of a control solution with one which has been treated and hydrolyzed with an enzyme (β-galactosidase). The enzyme catalyzes the splitting of glycosidic bonds and hydrolyzes GOSs and lactose into glucose and galactose. The concentration differences of free galactose and lactose determined in these two solutions is used to calculate the total GOSs (Figure 1).

Improvements to the AOAC Method

The sample preparation for AOAC 2001.02 is rather complex: one shortcoming is the incubation of the reference solution with the deactivated enzyme (which is rather expensive) to determine the initial carbohydrate concentrations (Figure 1) rather than using the pure extract. Another critical point is the sample dilution procedure, which is supposed to be done in acetonitrile, while standards are based on ultrapure water.

Here, the focus was to simplify the entire procedure to increase the ease of use and the overall efficiency of the method.

The improved method for total GOS content analysis uses the extract for measuring of the initial glucose, galactose, and lactose concentrations (Figure 1 Assay 1). However, the deactivated enzyme was not used, and instead comparisons were made to see if its presence had any effect on the results. This step was eliminated after proving results equivalent to AOAC 2001.02 Assay 1 (with the deactivated enzyme), but chemical expenses and additional manual work are reduced. The total GOS content is therefore calculated from the analyte concentrations in Assay 1 (without any enzyme) and Assay 2 (extract with the active enzyme) (Figure 2).

Figure 2. Overlaid chromatograms of Bimuno (prebiotic supplement), untreated (black) and treated with enzyme (orange).

Want to know more details about the application? Download our free Application Note AN-P-087 about total GOS analysis in foods with ion chromatography!

Aside from the enzyme usage, the official AOAC method for analysis of total GOSs suggests that standards be prepared in ultrapure water (UPW) while samples are to be diluted with 20% acetonitrile. A control experiment was performed to compare results between:

  • Dilutions in UPW evaluated with UPW calibration (“UPW option”)
  • Dilutions in acetonitrile evaluated with UPW calibration (AOAC 2001.02)
  • Dilutions in acetonitrile evaluated with acetonitrile calibration (“ACN option”)

Reproducibility of total GOS contents was compared among the three options, with the UPW and AOAC preparation options exhibiting similar results. The ACN option resulted in lower total GOS contents than the others. Additionally, the acetonitrile did not seem to lend a stabilizing effect to the samples. This supports the improvement of the AOAC method by performing sample dilutions with UPW instead of acetonitrile, saving unnecessary reagents and limiting the chemical imprint of the analysis.

Results

Overall, the satisfying variability, target and spike recoveries (Application Note AN-P-087), together with the interference tests proved the modified method as valuable and robust. With limits of detection (LODs) of 0.1 mg/L (galactose) and 0.2 mg/L (glucose, lactose) in solution, even low total GOS contents can be determined with high precision.

Summary

As a multicomponent method, ion chromatography with amperometric detection is a very selective, sensitive, and robust analysis method for carbohydrates without any additional derivatization steps. In combination with enzymatic treatment, even more complex carbohydrates can be quantified.

This research presents an update to the standard AOAC method for total GOS determination in foodstuffs. With the same principle (enzymatic hydrolysis of complex GOS molecules followed by chromatographic analysis of simple carbohydrates), analytical method efficiency was improved in favor of laboratory time and running costs. Additional automation steps (e.g., Metrohm Inline Dilution and automatic calibrations) can further improve the method efficiency.

Want more information about the simplified method for total GOSs via IC-PAD? More details about the improvement of AOAC method 2001.02 by reducing manual laboratory work and eliminating expensive reagents can be found in our article published in The Column from LC/GC (2021): Improving on AOAC 2001.02: GOS Determination in Foods Using HPAEC–PAD.

Read our article in LC/GC The Column (2021)

Improving on AOAC 2001.02: GOS Determination in Foods Using HPAEC–PAD

Post written by Dr. Alyson Lanciki, Scientific Editor 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.

Supercharge your battery research – Part 1

Supercharge your battery research – Part 1

Replacing traditional fuel-powered vehicles with battery-powered options is essential to reduce carbon dioxide (CO2) emissions. This greenhouse gas results from the combustion of fossil fuels, therefore limiting its input into the atmosphere will also influence global warming. Battery research therefore focuses on discovering new materials with higher energy and power density as well as a more efficient energy storage.

Various critical parameters need to be determined to develop viable new batteries. In this first of two blog posts, I want to highlight a few of the analytical parameters which can be determined using high precision analytical instruments from Metrohm and provide some free downloads in this research area.

What’s in a lithium battery?

Today, lithium ion batteries are the most common rechargeable batteries available on the market. A battery consists of an anode (negative pole) and cathode (positive pole). An electrolyte facilitates charge transfer in the form of lithium ions between these two poles. Meanwhile a separator placed between anode and cathode prevents short-circuits. An example cross section can be seen in Figure 1.

Figure 1. Cross-section illustration of a lithium ion battery. While the battery is being charged, lithium ions migrate from the cathode to the anode (from right to left), and during discharging they move from the anode to the cathode (from left to right).

The anode is made from graphite containing intercalated lithium applied to a copper foil, while the cathode consists of metal oxides dotted with lithium ions applied to an aluminum foil. The most common transition metals used in cathode materials are cobalt, nickel, manganese, or iron. The electrolyte is an anhydrous aprotic solvent containing a lithium salt (e.g., lithium hexafluorophosphate) to facilitate charge transfer. The separator is prepared from a porous material, acting as an insulator to prevent short-circuits. The composition of all of these components has a significant influence on the battery characteristics.

After this brief overview about the composition of a lithium battery, let’s take a look at selected key parameters and how they can be analyzed.

Water content in battery raw materials

Lithium-ion batteries should be free of water (concentration of H2O less than 20 mg/kg), because water reacts with the conducting salt (e.g., LiPF6) to form toxic hydrofluoric acid. Sensitive coulometric Karl Fischer titration is the ideal method for determining water content at trace levels. Water determination for solids is carried out using the Karl Fischer oven method – the residual moisture in the sample is evaporated and transferred to the titration cell where it is subsequently titrated. The working principle and advantages of the KF oven method are described in more detail in our blog post «Oven method for sample preparation in Karl Fischer titration».

For more details on how to carry out the water determination in one of the following battery components, download our free Application Bulletin AB-434:

 

  • raw materials for the manufacture of lithium-ion batteries
  • electrode coating preparations (slurry) for anode and cathode coating
  • the coated anode and cathode foils as well as in separator foils and in packed foil layers
  • electrolytes for lithium-ion batteries

Transition metal composition of cathode materials

The cathode of a lithium-ion battery is usually made from metal oxides derived from cobalt, nickel, manganese, iron, or aluminum. To produce the cathode, solutions containing the desired metal salts are used. For an optimized production process, the exact content of the metals present in the solution must be known. Additionally, the metal composition within the obtained cathode material should be determined. Potentiometric titration is a suitable technique to determine the metal content in starting solutions and the finished cathode materials.

The following mixtures of metals or metal oxides can be analyzed potentiometrically:

  • Nickel, cobalt, and manganese in solutions
  • Nickel, cobalt, and manganese in cathode materials such as cobalt tetraoxide (Co3O4), lithium manganite, or lithium cobaltite

For more details about the potentiometric analysis of a mixture of nickel, cobalt, and manganese download our free Application Note AN-T-218.

Analysis of lithium salts

Potentiometric titration is also ideally suited for determining the purity of lithium salts. For lithium hydroxide and lithium carbonate, the purity is determined using an aqueous acid-base titration. It is also possible to determine carbonate impurity within lithium hydroxide using this method.

For more details about performing the assay of lithium hydroxide and lithium carbonate, download our free Application Note AN-T-215.

For the assay of lithium chloride and lithium nitrate, the lithium is directly titrated using the precipitation reaction between lithium and fluoride in ethanolic solutions. For more details about how to carry out the assay of lithium chloride, download Application Note AN-T-181 and for lithium nitrate download AN-T-216.

The knowledge of other cations which might be present in lithium salts (and their concentration) is also of interest. Various cations (e.g., sodium, ammonium, or calcium) can be determined using ion chromatography (IC). IC is an efficient and precise multi-parameter method to quantify anions and cations over a wide concentration range.

The chromatogram in Figure 2 shows the separation of lithium, sodium, and calcium in a lithium ore processing stream.

Figure 2. Ion chromatogram of the lithium ore processing stream (1: lithium, 23.8 g/L; 2: sodium, 1.55 g/L; 3: calcium, 0.08 g/L).

For more information on how this analysis was carried out, download our free Application Note AN-C-189.

Eluated ions and decomposition products

In the development and optimization of lithium-ion batteries, one of the items of special interest is the content of ions (e.g., lithium, fluoride, and hexafluorophosphate) in the electrolyte or in eluates of different components. Ion chromatography allows the determination of decomposition products in electrolyte, or anions and cations eluated for example from finished batteries. Additionally, any sample preparation steps that might be required (e.g., preconcentration, dilution, filtration) can be automated with the Metrohm Inline Sample Preparation («MISP») techniques.

For more detailed information about selected IC applications for battery research, check out our Application Notes:

  • Cations in lithium hexafluorophosphate (AN-C-037)
  • Trace cations in lithium hexafluorophosphate (AN-CS-011)
  • Anions in electrolyte (AN-N-012)
  • Decomposition products of lithium hexaflurophosphate (AN-S-372)

Summary

This blog post contains only part of the analyses for battery research which are possible using Metrohm’s analytical instruments. Part 2 will deal with the electrochemical characterization of batteries and their raw materials. Don’t want to miss out? Subscribe to the blog at the bottom of the page.

If you want to see a complete overview about the analyses which are possible with our portfolio, have a look at our brochure on Battery research and production.

Battery research

Positive experiences with top quality Metrohm equipment!

Post written by Lucia Meier, Technical Editor at Metrohm International Headquarters, Herisau, Switzerland.

Chemistry of Chocolate

Chemistry of Chocolate

Swiss… Belgian… Pure… Milk…

Here we are in mid-February again, bombarded by chocolate from all sides in preparation for Valentine’s Day on the 14th. Whether in a solid bar, as a chewy truffle, or as a luxurious drink, chocolate has completely infiltrated our lives. Most people can agree that this confectionary treat is fantastic for any occasion – to be given as a gift, to recover after having a bad day, as well as to celebrate a good one – chocolate is certainly meant to be enjoyed.

Even if you don’t like the taste, the chances are high that someone close to you does. So how can you be certain of its quality?

Components of a chocolate bar

For the sake of this article, let us consider the humble chocolate bar, without any extra additions (not to mention any Golden Tickets). This form can be found worldwide in nearly any grocery store or candy shop, generally designated as white, milk, or dark.

All of this variability comes from the edible seeds in the fruit of the cacao tree, which grows in hot, tropical regions around the equator. They must be fermented and then roasted after cleaning. From this, cocoa mass is produced, which is a starting base for several uses. Cocoa butter and cocoa solids are prepared from the cocoa mass and are utilized in products ranging from foods and beverages to personal care items.

As for chocolate bars, these are generally sweetened and modified from the pure form, which is very bitter. Milk (liquid, condensed, or powdered) is added to many types, but does not necessarily have to be present. Varying the content of the cocoa solids and cocoa butter in chocolate to different degrees results in the classifications of dark to white. While some dark chocolates do not contain any milk, white chocolates do to add to the significant amounts of cocoa fat used to produce them.

In general, dark chocolate contains a high ratio of cocoa solids to cocoa butter and may or may not contain any milk. It may be sweetened or unsweetened. Milk chocolate is a much broader category, containing less cocoa solids but not necessarily a different cocoa butter content compared to dark chocolate, as milk fats are also introduced. Milk chocolate is also sweetened, either with sugar or other substitutes. White chocolate contains no cocoa solids at all, but a blend of cocoa butter and milk, along with sweeteners.

Depending on the country, there are different regulations in place regarding the classification of the type of chocolate. If you are interested, you can find a selection of them here.

What makes your favorite chocolate unique?

Of course, more ingredients are added to chocolate bars to affect a number of things like the aroma, texture/mouthfeel, and certainly to enhance the flavor. The origin of the cacao beans, much like coffee, can impart certain characteristics to the resulting chocolate. The manufacturing process also plays a major part in determining e.g., whether the chocolate has a characteristic snap or has a distinct scent, setting it apart from other brands.

In some cases, vegetable fats are used to replace a portion of the cocoa fats, although this may not legally be considered «chocolate» in some countries. The adjustment of long-standing recipes for certain chocolate brands has sometimes led to customer backlash, as quality is perceived to have changed. Truly, chocolate is inextricably tied to our hearts.

Applications for chocolate quality analysis

Nobody wants to give their Valentine a bad gift, especially out-of-date chocolate from a dubious source. Here, we have prepared some interesting analyses for different chocolate quality parameters in the laboratory.

Sugar analysis via Ion Chromatography (IC)

Most types of chocolate contain sugars or sugar substitutes to sweeten the underlying bitterness. Considering different regulations regarding food labeling and also nutritional content, the accurate reporting of sugars is important for manufacturers and consumers alike.

Sugar analysis in chocolate can be performed with Metrohm IC and Pulsed Amperometric Detection (PAD). An example chromatogram of this analysis is given below.

A small amount of commercially produced sweetened milk chocolate was weighed and dissolved into ultrapure water. After further sample preparation using Metrohm Inline Ultrafiltration, the sample (20 µL) was injected on to the Metrosep Carb 2 – 150/4.0 separation column and separated using alkaline eluent. As shown, both lactose and sucrose elute without overlap in less than 20 minutes.

Learn more about Metrohm Inline Ultrafiltration for difficult sample matrices and safeguard your IC system!

In this example, the sugar content was listed on the label as 47 g per 100 g portion (470 g/kg). Lactose was determined to be 94.6 g/kg, and sucrose was measured at 385.6 g/kg. To learn about what other carbohydrates, sweeteners, and more can be determined in chocolate and other foods with Metrohm IC, download our free brochure about Food Analysis and check out the table on page 25!

Lactose content in lactose-free chocolate

The accurate measurement of lactose in lactose-free products, including chocolate, is of special importance to consumers who are lactose-intolerant and suffer from digestive issues after eating it. Foods which are labelled as lactose-free must adhere to guidelines concerning the actual non-zero lactose content. Foodstuff containing less than 0.1 g lactose per100 g (or 100 mL) is most frequently declared as lactose-free.

Determination of lactose in chocolate is possible with IC. Here is an chromatographic overlay of a dissolved chocolate sample with lactose spikes which was analyzed via Metrohm IC using the flexiPAD detection mode.

Milk chocolate, labelled lactose-free measured via Metrohm IC (0.57 ± 0.06 mg/100 g lactose, n = 6).

The sample contained 0.6 mg lactose per 100 g, with measurement of the lactose peak occurring at 13.2 minutes. The black line is the unspiked lactose-free chocolate sample, red and blue are spiked samples of increasing concentration. To prepare the samples, approximately 2.5–5 g chocolate was dissolved in heated ultrapure water, using Carrez reagents to remove excess proteins and fats from the sample matrix. Afterward, centrifugation of the samples was performed, followed by the direct injection of the supernatant (10 µL) into the IC system. Measurement was performed with the Metrosep Carb 2 – 250/4.0 separation column and an alkaline eluent.

Interested in lactose determinations with ion chromatography? Download our free Application Notes on the Metrohm website!

Water determination with Karl Fischer Titration

The amount of water in foods, including chocolate, can affect their shelf life and stability, as well as contribute to other physical and chemical factors. Aside from this, during the processing stage, the amount of water present affects the flow characteristics of the chocolate mass.

AOAC Official Method 977.10 lists Karl Fischer titration as the accepted analysis method for moisture in cacao products.

The determination of moisture in different chocolate products is exhibited in the following downloadable poster. As an example, several samples (n = 10) of dark chocolate (45% cocoa content) were analyzed for their moisture content with Metrohm Karl Fischer titration.  Results were found to be 0.96% water with a relative standard deviation (RSD) of 2.73%. More information about this analysis can be found in our poster about automated water determination in chocolate, or in chapter 11.6 of our comprehensive Monograph about Karl Fischer titration.

Oxidation stability with the Rancimat test

Oxidation stability is an important quality criterion of chocolate as it provides information about the long-term stability of the product. Cocoa contains various flavonoids that act as antioxidants. Although the flavonoid content may vary amongst chocolate type, in general, the greater the content of cocoa solids in the chocolate, the greater its antioxidant effect.

The 892 Professional Rancimat from Metrohm determines the oxidation stability of fat-containing foods and cosmetics. The Rancimat method accelerates the aging process of the sample and measures the induction time or oxidation stability index (OSI).

Chocolate cannot be measured directly with the classical Rancimat method, as no evaluable induction time is obtained. There are many reasons for this: e.g., the fat content is too low. Traditionally, extraction of the fat from the chocolate is necessary, but not always.

Learn more about the Rancimat method on our website, and download our free Application Note about the oxidation stability of chocolate. In this Application Note, the oxidation stability of white, milk and dark chocolate is determined without extraction.

Cadmium in chocolate by Voltammetric analysis

The toxic element cadmium (Cd) can be found in elevated concentrations with high bioavailability in some soils. Under such conditions, cacao trees can accumulate cadmium in the beans. Chocolate produced from the affected beans will contain elevated cadmium levels.

Typical limit values for Cd in chocolate in the European Union are between 100 µg/kg and 800 µg/kg (EU Commission Regulation 1881/2006) depending on the cocoa content of the chocolate. Anodic stripping voltammetry (ASV) can be used to accurately determine trace quantities of cadmium in chocolate down to approximately 10 µg/kg. The method is simple to perform, specific, and free of interferences.

Chocolate samples are first mineralized by dry ashing in a furnace at 450 °C for several hours. The remaining ash is then dissolved in an acidified matrix. The cadmium determination is then carried out on the 884 Professional VA instrument from Metrohm. To learn more about how to perform the analysis, download our free Application Note.

Happy Valentine’s Day from us all at Metrohm!

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