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Chemical analysis of sourdough: pH and total titratable acidity (TTA)

Chemical analysis of sourdough: pH and total titratable acidity (TTA)

Like many, I am fascinated by the chemistry behind baking, and in this blog I want to talk about bread—sourdough in particular. There is a well-known saying in the baking industry: «The pH value bakes and the total titratable acidity tastes». Why are these two parameters important for baking bread, and how can they be determined in the best way? This is what I want to discuss here.

A brief history of sourdough

Bread has been part of the human diet for several thousand years, although not necessarily in the forms we are familiar with today. One exception to this is sourdough bread. Wild yeast and bacteria (lactobacilli) ferment the dough naturally, creating a tangy loaf full of crevices. Despite originating in the Fertile Crescent, one of the oldest physical examples (at nearly 6,000 years old) was excavated in Switzerland, showing how widely it spread by that point already.

Currently, one of the places most well-known for its sourdough bread is San Francisco, in California. Why California? Bakers from France brought their techniques there during the Gold Rush in the mid 1800’s, and it has since become ubiquitous with the city. In fact, San Francisco has its own eponymous strain of sourdough bacteria: Fructilactobacillus sanfranciscensis.

Sourdough bread loaf full of crevices
Figure 1. Cross section of a sourdough bread loaf.

Many home bakers try to make sourdough at some point, since the ingredients are simple and no leavening agent is used, except for what nature provides. However, with so many people at home during 2020–2021, it was an ideal time for many people to see what they could produce. The development of the starter is of key importance—if there is not sufficient wild yeast and bacteria (or they do not have enough nutrients), then the dough will not rise, and you are left with a dense, chewy result. (While much has been written about how to make the best homemade sourdough, I cannot contribute to this topic, as my own baking spree focused on the Swiss Butterzopf.)

Click here to download the recipe and try it out yourself!

Lactobacilli: helpful bacteria

As their name suggests, lactobacilli produce lactic acid (Figure 2) and also acetic acid, and these give the sourdough bread its characteristic tangy, sour taste. The sourness of the bread also has positive effects on its shelf life, making it possible for our ancestors to preserve the bread for a longer time to supplement their diet.

There is another reason why the presence of this helpful bacteria is important. Without the lactic and acetic acid, it would be impossible to bake bread made from rye flour, which is commonly used in sourdough bread of northern Europe. How come?

Figure 2. Chemical structure of lactic acid.

Starch is the key component within bread and influences the shape, crumb consistency, and overall flavor. During the baking process, gelatinization occurs between the starch within the flour and the water added to the dough. However, flour also contains the enzyme amylase, which catalyzes the hydrolysis of starch into sugar. During the gelatinization process, starch is more prone to hydrolysis by amylase. Strong amylase activity at this point will have detrimental effects on the bread crumb. For wheat, the amylase is already denatured at the temperature gelatinization begins within the dough. This is not the case for rye, which gelatinizes at a lower temperature when amylase activity happens to be the highest [1]. By making an acidic (sour) dough, the amylase activity is inhibited and it becomes possible to bake bread made from rye flour.

So how much acid is necessary and when is it too much? This question brings us back to the two key parameters, pH value and total titratable acidity (TTA), I mentioned in the introduction.

Figure 3. Fermenting sourdough starter in a glass jar.

pH value regulates enzyme activity

The pH value is important to inhibit amylase in an  optimal manner. Every enzyme has an optimal pH range in which it functions the most efficiently. For amylase, the optimal pH value (highest enzyme activity) ranges from pH 5.4 to 5.8. At a lower pH value its activity will be reduced.

The pH value can be easily measured using a pH electrode. For dough analysis, an electrode such as the Spearhead electrode which can pierce into the sample is the best sensor. As the pH value is temperature dependent, the sensor measures the temperature as well.

What is the pH value?

The pH value is the negative logarithm of the hydronium concentration. Therefore, the smaller the pH value, the higher the hydronium concentration.

Pure water itself contains a small amount of free hydronium ions, and its pH value is therefore 7.

As acids release hydronium ions when they are in solution (dissociation), acidic solutions have pH values between 0 and 7. 

Contrary to this, alkaline solutions and products have even less hydronium ions than pure water. They have pH values ranging from 7 to 14. An example of an alkaline solution is lye, which is used to produce lye rolls.

For more information on pH measurement check out our other blog posts «Avoiding the most common mistakes in pH measurement» and «FAQ: All about pH calibration».

Total titratable acidity helps assess the taste

Why do we need to determine the total titratable acidity (TTA) if measuring and controlling the pH value is sufficient to regulate the amylase activity? This is because the pH value does not provide any information about the ratio of lactic acid and acetic acid present in the dough. While the amylase activity is not dependent on the ratio of the two, the composition is important for the taste. For optimal sourdough flavor, the ratio of lactic acid to acetic acid should lie between 3:1 and 4:1. If the ratio shifts towards containing more acetic acid, the taste usually becomes too sour.

Weaker acids such as lactic acid and acetic acid do not completely dissociate, meaning not all acid molecules present will release their hydrogen ion. As lactic acid is a stronger acid in comparison to acetic acid, more lactic acid will dissociate and thus contribute more to the pH value. By determining the TTA, it is possible to find out what the total amount of acids is within the dough.

For the determination of the TTA, dough is homogenized with water to obtain a suspension. It is then titrated to a pH value of 8.5 with 0.1 molar sodium hydroxide solution. The use of an automated titrator provides reliable results without human interference (Figure 4).

Figure 4. A robust and compact titrator for the determination of the total titratable acidity

Before the titration starts, the pH value of the suspension can be determined easily, so you get both parameters (pH value and TTA) without needing to do double the work. For more detailed information on how the analysis is done, download our free Application Note.

pH value and TTA for the perfect sourdough quality

By combining the information about the pH value and TTA it becomes possible to assess the quality of sourdough and thus maintain a constant quality in the final product, especially if delays in the production process occur.

It also becomes possible to detect changes in the sourdough starter which might occur if storage conditions cannot be maintained, and thus provide critical information when it is time to prepare a new starter.

Table 1. Common pH and TTA values for various kind of breads [1].
Bread type pH value TTA
Wheat bread 5.4–6.0 4–6
Wheat mixed bread 5.0–5.3 6–8
Rye mixed bread 4.5–4.8 7–9
Rye bread 4.3–4.7 8–10
Rye bread (coarsely ground) 4.2–4.6 9–14

Lessons learned

I hope this blog post on the chemistry of sourdough has given you some new insights on this fascinating kind of bread.

As for myself, I will probably not venture into the sourdough baking arena but stick with my homemade Butterzopf.

Figure 5Butterzopf (made by the author): a traditional Swiss bread usually consumed on Sundays for brunch.

If you are interested in other blog articles related to yeast, check out our post about beer brewing: «Making a better beer with chemistry». If you have more of a sweet tooth then read our blog post on the «Chemistry of chocolate».

The chemistry of bread

Straightforward determination of pH value and total titratable acidity (TTA) in dough

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

Easy moisture determination in fertilizers by near-infrared spectroscopy

Easy moisture determination in fertilizers by near-infrared spectroscopy

Blooms or bombs?

As the global population steadily increases, it is important that sufficient crops are produced each year to provide enough food, clothing, and other products. Crops such as corn, wheat, soy, and cotton receive nutrients from the soil they are grown in. Fertilizers play a crucial role in providing these crops with the nutrients they need to grow properly.

An important ingredient in the production of high quality, effective fertilizers is ammonium nitrate (NH4NO3), a good source of nitrogen and ammonium for plants.

Produced as small beads similar in appearance to kitchen salt, ammonium nitrate is cheap to buy and usually safe to handle – but storing it can be a problem. Over time, the compound absorbs moisture, which leads to clumping of the individual beads into a larger block. When such a large quantity of compacted ammonium nitrate is exposed to intense heat it can trigger an explosion.

Over the last century, ammonium nitrate has been involved in at least 30 disasters and terrorist attacks. One of the most recent occurrences was on the evening of August 4th, 2020 in Beirut, where an ammonium nitrate explosion killed at least 220 people and injured more than 5000. This blast is one of the largest industrial disasters ever linked to NH4NO3.

Moisture analysis methods for fertilizers

During the production process of ammonium nitrate it is important to control the moisture content. A low moisture content is preferable, but unnecessary excess drying leads to additional manufacturing costs.  Regulations for different fertilizers vary across the globe, but local legal limits ensure that the maximum amount of water present must not be exceeded.  Therefore,  rapid, reliable, and accurate methods for the determination of moisture is necessary. Out of those available, Karl Fischer titration is one of the most common; oven drying, for example, cannot be used with fertilizers containing ammonium nitrate.

Compared to these methods, near-infrared spectroscopy (NIRS) offers unique advantages. It is a secondary technique that generates reliable results within seconds without needing any sample preparation. NIRS is a non-destructive measurement technique and at the same time does not create any chemical waste.

Read our previous blog posts below to learn more about NIRS as a secondary technique.

NIRS analysis of solids

The most suitable NIR analyzer to measuring different parameters in fertilizer or ammonium nitrate pellets is the Metrohm DS2500 Solid Analyzer with Large Sample Cup.

Solid samples (e.g., granules and pellets) that are filled in the rotating DS2500 Large Sample Cup must be placed on the analyzer window. While scanning the sample, the Large Sample Cup will rotate in order to compensate for inhomogeneity.

As the DS2500 Solid Analyzer is a pre-dispersive system, the sample is illuminated with monochromatic light in order to keep the energy level as low as possible. Therefore, the instrument lid must be closed prior to starting the analysis so external light does not affect the results. The NIR radiation comes from below and is partially reflected by the sample to the detector, which is also located below the sample vessel plane. After 45 seconds, the measurement is completed, and a result is displayed. As this reflected light contains all the relevant sample information, this measurement technique is called diffuse reflection.

Advantages of using NIRS

The procedure for obtaining the NIR spectrum already highlights its simplicity regarding sample measurement and its speed. Several advantages of NIRS are listed below:

 

  • Fast technique with results in less than 1 minute.
  • No sample preparation required – solids and liquids can be used in pure form.
  • Low cost per sample – no chemicals or solvents needed.
  • Environmentally friendly technique – no waste generated.
  • Non-destructive – precious samples can be reused after analysis.
  • Multiple component analysis – prediction of different constituents in parallel.
  • Easy to operate – inexperienced users are immediately successful.

Overall, near-infrared spectroscopy is a robust alternative technique for the determination of both chemical and physical parameters in solids and liquids. It is a fast method which can also be successfully implemented for routine analysis by staff without any higher laboratory education.

Related Applications

Specialty chemicals have to fulfill multiple quality requirements. One of these quality parameters, which can be found in almost all certificates of analysis and specifications, is the moisture content. The standard method for the determination of moisture content is Karl Fischer titration.

This method requires reproducible sample preparation, chemicals, and waste disposal. Alternatively, near-infrared spectroscopy can be used for the determination of moisture content. With this technique, samples can be analyzed without any preparation and without using any chemicals.

More information about the application details can be found below!

Moisture content is one of the most commonly measured properties of fertilizers. Globally, regulations for different fertilizers vary, but local legal limits ensure that the maximum amount of water must not be exceeded. A number of analytical techniques are available for this purpose. Next to gravimetric methods, Karl Fischer titration is often used for accurate moisture determination.

Compared to these methods, near-infrared spectroscopy offers unique advantages: it generates reliable results within seconds, and at the same time does not create chemical waste. This Application Note explains how NIRS can offer fast, reagent-free analysis of moisture content in various fertilizer products.

Read on for more technical details…

To learn more about how Karl Fischer titration and NIRS complement each other for the analysis of moisture in different products, read our blog post!

For more information

About spectroscopy solutions provided by Metrohm, visit our website!

We offer NIRS for lab, NIRS for process, as well as Raman solutions

Post written by Wim Guns, International Sales Support Spectroscopy 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.

ASTM D6304: Easier determination of moisture in petroleum products

ASTM D6304: Easier determination of moisture in petroleum products

Water in petroleum products, such as lubricating oils, jet fuel, or other similar products can have deleterious effects. Moisture is often associated with corrosion and engine wear. Knowing the water content of petroleum products can prevent damage to costly infrastructure and ensure safer operations.

ASTM D6304 «Standard Test Method for Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl Fischer Titration» is a standard that is often cited for moisture determination in the specifications of various petroleum products. It has been recently updated (January 2021) and now offers three procedures for accurate moisture determination.

The direct sample injection into the titration cell (Procedure A) is recommended for low viscosity samples without expected interferences. An oven (Procedure B) or water evaporator accessory (Procedure C) can be used to analyze samples that do not readily dissolve in Karl Fischer reagent, viscous samples, and samples with components that are expected to interfere with the Karl Fischer reaction.

In this blog post I want to introduce these three procedures, and then discuss when it is appropriate to use each of them.

Determining the moisture content in petroleum products doesn’t have to be messy. Visit our website to learn more about the new automated measurement capabilities allowed with ASTM D6304.

A coulometric Karl Fischer Titrator such as the 851 Titrando from Metrohm is the basis for all three procedures of ASTM D6304.

Direct injection (Procedure A)

The direct sample injection into the titration cell is recommended for low viscosity samples without expected interferences. An aliquot of known mass or volume is injected into the conditioned titration cell of a coulometric Karl Fischer apparatus, where it is titrated automatically, and the results calculated.

Method D6304 permits the use of coulometric generator electrodes with and without diaphragm. We recommend the use of the generator electrode with diaphragm, due to the low water content of the samples.

Not all petroleum products are soluble in Karl Fischer reagent and phase separation can occur when using Procedure A. If phase separation occurs, the reagents need to be replaced. The number of samples which can be analyzed without phase separation depends on the volume and type of sample, the volume of reagent, and the sample solubility in the reagent.

The generator electrode with diaphragm is recommended for water determination according to ASTM D6304 Procedure A.

However, for these kinds of samples, Procedures B or C are often the better solution. The same is the case if your sample contains interfering substances.

For more information about ASTM D6304 Procedure A, download our free Application Bulletin (AB-209). For more tips and tricks about how to improve your Karl Fischer titration, have a look at our blog series: «Frequently asked questions in Karl Fischer titration».

Water extraction using an oven (Procedure B)

An oven (Procedure B) can be used to analyze samples that do not readily dissolve in Karl Fischer reagent, viscous samples, and samples with components that are expected to interfere with the Karl Fischer reaction.

For the analysis, a representative sample is weighed into a glass vial, which is sealed immediately. The vial is then heated in an oven to extract any water. The vaporized water is carried into the conditioned Karl Fischer titration cell by means of a dry carrier gas where it is titrated.

Schematic drawing of the Karl Fischer oven method.

The ideal temperature used for the evaporation depends on the sample. The 874 Oven Sample Processor can perform a temperature gradient test to determine the optimal temperature for removing water without degrading the sample.

To learn more about the oven method, its working principle and its advantages, check out our blog post: «Oven method for sample preparation in Karl Fischer titration».

Watch our LabCast video below to see the working principle and advantages of using Procedure B.

For more information about using the KF oven method for ASTM D6304 Procedure B, download our free Application Bulletin (AB-209) or free Application Note (AN-K-070).

Just want the highlights? Have a look at our short flyer about how ASTM D6304 has become much easier!

Water extraction using an evaporator (Procedure C)

Instead of using an oven, Procedure C explains how a water evaporator can be used for the water extraction of samples that do not readily dissolve in Karl Fischer reagent, viscous samples, and samples with components that are expected to interfere with the Karl Fischer reaction.

In this procedure, an aliquot of sample is transferred into a heated chamber containing a suitable solvent (most often, toluene). The temperature of the heated chamber depends on the solvent used. The water vaporizes along with the solvent in an azeotrope distillation. The azeotrope is then transferred into the conditioned Karl Fischer titration cell via a dry non-reactive carrier gas. 

Schematic drawing of the evaporator method.

If you wish to read more about the three procedures and their advantages and disadvantages, download our White Paper: «Moisture in petroleum products according to ASTM D6304».

When to use which procedure

Procedure A is mainly suited for liquid samples with a low viscosity, such as diesel fuel, jet fuel, or aromatics. A low viscosity is required in order to be able to add the sample easily into the Karl Fischer titration cell. Furthermore, the samples require a good solubility in Karl Fischer reagent. Otherwise phase separation will occur, which requires the replacement of the Karl Fischer reagents. While the reagent exchange can be automated, time is still required until the reagents reach dryness again.

Even if samples are soluble in Karl Fischer reagents, there might still be issues with using Procedure A due to the sample matrix creating side reactions and thus false results. In this case Procedure B or C are the better option.

Procedure B is suitable for all kinds of samples, regardless of their viscosity or matrix composition. It is only the evaporated water that is transferred into the titration cell, leaving the sample as well as interfering matrix components remaining in the sealed vial, which can be simply disposed of after the analysis. For this reason, the reagent exchange frequency is greatly reduced, saving costs, as less reagent is required. Depending on the workload in your lab, it is even possible to fully automate the analysis including reagent exchange using an automated Karl Fischer oven.

The 874 Karl Fischer Oven Processor with an 851 Titrando for a fully automated analysis according to ASTM D6304 Procedure B.

Procedure C, like Procedure B, is suitable for all kinds of samples, regardless of their viscosity or matrix constitution. It is only the evaporated water in an azeotrope with the solvent that is transferred into the titration cell. The sample, as well as interfering matrix components, remain in the evaporation chamber. However, it is necessary to manually empty and refill the evaporation chamber from time to time, which is time consuming, as the chamber needs to cool down before the content can be exchanged. Furthermore, walk-away automation is not possible with this method.

For a more detailed comparison of the various factors for each procedure, download our free White Paper: «Moisture in petroleum products according to ASTM D6304».

Visit our website

Save time with the new automated measurement capabilities allowed with ASTM D6304

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

«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.

Oven method for sample preparation in Karl Fischer titration

Oven method for sample preparation in Karl Fischer titration

Maybe you have experienced one of the following situations in the laboratory. You need to determine the water content of a sample using Karl Fischer titration and you realize one or more of these issues:

  • The sample does not dissolve in the KF reagent. No solubilizer helps, the sample is still not dissolving, and the results are far from reproducible.
  • The sample reacts with the KF reagent. The titration does not stop, and there is no endpoint detected.
  • The sample contaminates the titration cell and the electrode(s). Even if you replace the reagent after every measurement, the obtained results are out of specification.

There is a way to solve the above-mentioned problems. Trust me—it’s fantastic!!

The solution is the oven method or gas extraction technique.

What is Karl Fischer titration? Download our free Monograph to learn more from the experts.

What is the oven method?

The oven method is a sample preparation technique used in Karl Fischer titration to analyze samples…

For more help, take a look at our frequently asked questions in Karl Fischer titration under the section «Sample Handling» here on our website:

The principle is very simple.

The sample is weighed into a headspace vial and closed with a septum cap. When placed in an oven, the water evaporates and a carrier gas (usually air or nitrogen) dried with a molecular sieve transports the released water into the titration cell, where the determination of the water content takes place. The water is separated from the sample matrix, avoiding side reactions and contamination.

The temperature of the oven is chosen according to the temperature stability of the sample. This leads to the question to which temperature the sample should be heated. What is the optimal oven temperature?

Finding the optimal oven temperature

Using a suitable oven temperature to analyze a sample is crucial to obtain the correct results. The oven temperature should be as high as possible, within reason. This guarantees a fast and complete release of the water and subsequently, short titration times. However, you should avoid choosing a temperature that is too high. Decomposition of the sample usually leads to the formation of unwanted substances that can falsify the water content. Therefore, as a rule of thumb, I recommend choosing an oven temperature 20 °C below the decomposition temperature of the sample.

But what can you do if you have no idea at which temperature your sample should be analyzed? No worries! There are several ways to find the optimal oven temperature.

One possibility is to search in the literature. The more information on temperature stability of the sample you find, the better off you will be. If you are able to find a decomposition temperature, it will help immensely to define the optimal oven temperature. Maybe you are lucky and someone else has already analyzed the same sample; then you may also find a recommended oven temperature. A good start is reading our free Application Bulletin AB-280, which lists several substances.

Are you searching for Karl Fischer titration oven applications? Look no further – the Metrohm Application Finder contains several applications you can download for free! Check them out here:

If literature research does not reveal a suitable oven temperature, you must determine it yourself. How this is done depends upon the type of instrument you are using.

Some instruments offer you the possibility to run a so-called temperature gradient or temperature ramp. The sample is heated at a constant rate (e.g., 0.5 °C or 2 °C per minute) in a defined temperature range (e.g., 50 to 250 °C). At the same time, the released water is determined. In the end, the software will display a curve, showing you the released water as a function of the temperature. The following graph shows an example of such a temperature gradient curve.

The blue line corresponds to the determined water content, whereas the orange line indicates the drift value. An increasing drift signals the release of water, but it can also be a sign for decomposition, especially if the drift no longer decreases to a low level. In this graph, the drift peak at 50 °C corresponds to the blank value and free water. Between 120 and 200 °C, the drift value increases again, meaning the sample releases water. Then the drift decreases and remains low and stable up to 250 °C. There are no signs of decomposition up to 250 °C. As we do not know what would happen at temperatures above 250 °C, the optimal oven temperature for this sample is 230 °C (250 °C – 20 °C = 230 °C).

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

Here is an example of a sample which started to decompose at temperatures above 106 °C (left sample vial) and thus is turning brown. An optimal temperature would therefore be 85 °C.

Sample analysis with a KF oven – step by step

After you have found the optimal oven temperature, water content determination in the sample can begin.

  • First, I recommend to run a system preparation. This means running a determination, but with an empty sample vial. During this preparation step, all tubes in the system are purged with dried carrier gas, and any traces of water are removed.
  • Next, you need to determine the blank value. The sample vials and the caps contain some residual moisture. With the blank determination, the amount of water contained in an empty sample vial is determined. The mean value of e.g. 3 blank value determinations is then subtracted from the water content obtained for the samples.
  • Finally, you can analyze the samples.

Please keep in mind that the same parameters for the system preparation, the blank value determination, and the sample determination must be used. This is of importance if you want to measure a check standard before and/or after the sample analysis or sample series. If the optimal oven temperature for the standard is different from the one for the sample, I recommend that you determine a blank value for the standard as well.

Checking an oven system

There are special, solid water standards available to check the performance of an oven system. These water standards are perfect to inspect the complete oven system and to ensure that the evaporated water reaches the titration cell and is determined there. Such standards include a certificate stating the water content.

Using the certified value, you can calculate the recovery when determining the water content of the standard with the oven. If the recovery value is between 97–103%, everything is fine. However, if the recovery is outside this range, the oven system should be checked for leaks or water deposits. It might be that only the molecular sieve needs to be exchanged. Possibly, the reagent is exhausted and needs to be replaced.

There are other reasons which explain recovery values which are too high or too low. The reason must be found, as incorrect recovery values also mean that the determined sample water content is wrong. Have a look at our free Application Bulletin 280 for detailed information on troubleshooting an oven system.

Summary

The oven method is a simple and convenient way to analyze difficult samples. Side reactions are reduced to a minimum. The titration cell and the reagent are not contaminated with sample. In case you have to analyze a large series of samples, automation of the oven method is possible. Have a look at the available instruments for the oven method on our website!

Want to learn more

about Karl Fischer titration

Watch our free webinars here!

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