The Scientific*gear Blog

How to Clean Karl Fischer Electrodes:

A Karl Fischer titrator uses two electrodes: the inner burette, also known as the generator electrode, and the detector electrode. This guide provides general cleaning and care recommendations to help maintain both electrodes.

Cleaning with alcohol: general method

Recently, we worked with a customer who owns one of our Volumetric Karl Fischer Titrators (MKV-710) and was experiencing unexpected issues when testing samples with high moisture content. Specifically, the customer observed that certain samples appeared to max out at around 1% moisture, after which the titrator would go into over-titration. Interestingly, this behavior only occurred with specific sample types.

To get to the root of the issue, we stepped back and reviewed the fundamentals of volumetric Karl Fischer titration. This back-to-basics approach helped clarify what was happening—and revealed several practical troubleshooting steps that may help others facing similar challenges.

Understanding the Basics

The MKV-710 Volumetric Karl Fischer Titrator is designed to measure moisture content from trace levels all the way up to 100% water, so measuring above 1% moisture should not be a limitation of the instrument itself.

Reagent Factor Check

The customer provided data showing that the Karl Fischer reagent factor was properly calculated using Honeywell Hydranal Composite 5, with a factor of:

5.0796 mg/mL

This is a very reasonable value and indicates the reagent and factor calculation were done correctly. Great start.

What Causes Over-Titration?

Over-titration occurs when the instrument delivers more Karl Fischer reagent than is required for the amount of water actually present in the titration cell.

Here’s how the process works:

• The detector electrode senses moisture in the titration vessel.

• It signals the titrator to dose Karl Fischer reagent (Composite 5).

• The reagent reacts with and neutralizes the water.

• Once all moisture is consumed, the electrode stops detecting water.

• The instrument then calculates total water based on how much reagent was used.

If the electrode receives inaccurate information, the titrator may continue dosing reagent—leading to over-titration.

The Math Behind the Measurement

Understanding the math helps clarify what the instrument is doing:

• Composite 5 reagent neutralizes approximately 5 mg of water per mL

• 1 mg = 1,000 micrograms

• Therefore, 1 mL of reagent ≈ 5,000 micrograms of water

• All Karl Fischer titrators measure moisture in micrograms

Key Conversions

• 10,000 ppm = 1.0% moisture

• 5,000 ppm = 0.5% moisture

• 1,000 ppm = 0.1% moisture

Moisture Calculation Formula

As long as the sample size is known, the moisture result can be accurately calculated from the amount of reagent consumed.

Common Causes of Over-Titration

If the instrument is overdosing reagent, a few common issues may be responsible:

1. Detector Electrode Issues

A faulty or aging detector electrode may not correctly sense when all moisture has been neutralized, sending incorrect signals to the titrator.

2. Poor Sample Mixing (Very Common)

If the sample does not dissolve or homogenize properly in the titration solvent, moisture can exist in localized “pockets.” This can confuse the detector electrode and cause continued dosing.

Solution:
Improve sample mixing and solubility. In some cases, adding a co-solvent such as xylene can significantly help break down the sample.

Pro Tip: Xylene can be added at up to 20% of the total sample volume to improve solubility.

Additional Pro Tips for Reliable Results

1. Verify Instrument Performance
   Run a water check using a micro-drop of pure water. A recovery of 99% or higher confirms the titrator can accurately measure high moisture levels. When combined with a successful factor check, this strongly indicates the instrument is working correctly.

2. Increase Pre-Stirring Time
   If samples have solubility challenges, adjust the method to stir for 60 seconds before titration begins. This simple change can dramatically improve consistency.

3. Use Mixed Solvents When Needed
   For stubborn samples, try a solvent blend such as 80% methanol / 20% xylene to improve dissolution.

4. Watch for Chemical Interferences
   Samples containing ketones, aldehydes, or problematic pH levels can interfere with Karl Fischer reactions and should be evaluated carefully.

Final Thoughts

When high-moisture samples appear to “max out” or cause over-titration, the issue is often sample-related rather than instrument-related. Verifying the basics—reagent factor, instrument performance, electrode condition, and sample mixing—can quickly narrow down the root cause.

A systematic troubleshooting approach not only resolves the immediate problem but also builds confidence in the results moving forward.

Yes, ketones can potentially affect moisture readings in Karl Fischer titration. This is because ketones can react with the methanol in common Karl Fischer reagents, forming acetals, which also react with the reagent and produce water. This additional water is then titrated and can cause the moisture reading to be too high. In order to avoid this, it is important to ensure that the titration cell is cleaned thoroughly after each analysis to remove any traces of ketones that may be present. If traces of ketones are left in the cell, it can cause erroneous readings and affect the overall accuracy of the moisture measurement.  Additionally, there are some specialty reagents, Coulomat AK and Coulomat CGK,  that can be used to help limit this side reaction....and also you have the option of using a Volumetric Karl Fischer Titrator to get around this problem.

This might sound a bit technical but has significant importance in the world of chemistry: validating burettes on an automatic titrator.

For those who are not familiar with burettes, they are glass tubes used in laboratories to measure the volume of liquid dispensed. They are essential in titration, a process of chemical analysis used to determine the concentration of an unknown solution by reacting it with a known solution.

An automatic titrator, on the other hand, is a device used to automate the titration process. It reduces human error, increases precision, and saves time. However, to ensure accurate results, it is crucial to validate the burettes used in the titrator.

Now, let me get personal and share a story. I once worked in a lab where we had a faulty burette that was not calibrated correctly. We did not realize it until we compared our results with another lab, and they were different. We had to redo all our tests, causing a significant delay in our research. It taught me the importance of validating instruments before conducting any experiments.

To validate a burette, we need to check its accuracy by measuring the volume of liquid it dispenses. We can use a standard solution of a known concentration to verify the accuracy and precision of the burette. This process ensures that the titration results are reliable and trustworthy.

Here's a random fact related to the topic. Did you know that the burette was invented by a French chemist named Francois Antoine Henri Descroizilles in 1824?

To sum this all up,  validating burettes on an automatic titrator is crucial to ensure accurate results in chemical analysis. It may seem like a small step, but it can make a significant difference in research and experiments. So, let's not overlook the importance of this process and always validate our instruments before conducting any tests.

P.S, Check out our Burette Validation & Repair Service. 

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Accurate measurement of moisture content is essential to ensure the quality and consistency of your products. There are several methods available for measuring moisture content, but one of the most reliable and accurate methods is Karl Fischer moisture titration.

Karl Fischer moisture titration is a widely used method for measuring moisture content in a variety of materials, including solids, liquids, and gases. This method is based on the reaction between water and a Karl Fischer reagent, which produces a measurable electrical signal. The amount of water present in the sample can be calculated from the electrical signal, providing a precise measurement of moisture content.

One of the main benefits of using Karl Fischer moisture titration is its high accuracy. This method can detect moisture levels as low as 0.001%, making it ideal for applications where even small amounts of moisture can have a significant impact on product quality. In addition, Karl Fischer moisture titration is highly selective, meaning that it only reacts with water and not other substances in the sample. This makes it an excellent choice for measuring moisture content in complex mixtures.

Another advantage of Karl Fischer moisture titration is its versatility. This method can be used to measure moisture content in a wide range of materials, including pharmaceuticals, food products, and industrial chemicals. It can also be used to measure moisture content in gases, making it an essential tool for applications such as natural gas processing and semiconductor manufacturing.

Compared to other methods for measuring moisture content, Karl Fischer moisture titration is also relatively fast and easy to perform. The titration process can be automated, reducing the risk of human error and increasing efficiency. This makes it an excellent choice for high-throughput applications where speed and accuracy are essential.

Share this with associates who may find  an analysis of Karl Fischer titration useful.

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If you want to know more about Total Base Number (TBN) then this is for you.  In this webinar we cover both of the popular ASTM methods, ASTM D2896-21 and ASTM D4739-17.  This is a great training webinar for those who are just learning about it and for those seasoned pros who need a little refresher training.

We will do our best to answer:

• What is TBN (Total Base Number)?
• Why do we test for TBN (Total Base Number)?
• How do we test for TBN (Total Base Number)?
• How to setup the titration application on an automatic titrator
• Common problems to avoid
• Best practices you should follow

This is an on-demand webinar where you will be able to download information as well as the presentation.  You can communicate with us in real time via email while you watch the webinar.  The webinar is about 45 minutes long and even has a short quiz at the end.

In this short 30 minute webinar we dive into understanding the common titration application known as TAN or "total acid number", also known as,  ASTM D664.  As part of our titration webinar series we have a fun and uncomplicated talk about this titration application known as "total acid number".  

In this short but informative webinar we explore:

• What is TAN, total acid number, ASTM D664?
• Why do we test for it?
• How do we test for it?
• How do you set up the titration application?
• What are common problems you need to avoid?
• Best practices you should know about and try to follow

It only takes a few seconds to register for this highly interactive webinar (recorded).  You will be able to watch, send us emails with questions, download various application resources including the application notes, electrode prep tips, and more.

This is a valuable tool for seasoned experts and first timers.

There are still many who test salt content by hand and so the thought of using an automatic titrator might sound intimidating.  It's not. Really.  So we thought it would help if we made some videos to explain some of the basic steps involved and show for those who have never seen one what a titrator looks like.  To be sure there are many capable titrators that can do the job so don't get completely caught up in which one is best but think more about the benefits of automating a test that is repeated many times daily.  

In the following videos we provide a step by step look at how a sample (potato chips) would be prepared and tested using an automatic titrator with the help of a 6 position sample changer.  

VIDEO DEMONSTRATION:  Testing Salt in Potato Chips with Titrator

WHAT YOUR GOING TO NEED IN ADDITION TO THE TITRATOR:

1. Silver Nitrate; 1.0 or 0.1 normal strength (This is the titrant that you will use)

2. Combined silver electrode (it's a silver and pH electrode combined)

THINGS YOU SHOULD KNOW:

1.  How do you currently prep your sample.  This process should not really change.  Sample prep is important though and should be considered.

2. Know the ingredients of your sample.  You should have a pretty good idea about the types of chlorides and sodium that may be found in your sample.

Get More Information on Salt Testing Equipment.  Click here

We get this question a lot.  So, we decided to try and figure it out the best we can.  In this analysis, we are only going to examine and include the per-unit cost of the titrator (automatic) and the reagents (silver nitrate - AgNO3).  It seems we could include other factors including human resources and electrical power requirements but these can vary greatly so we will leave them out of this analysis.  Additional ancillary costs can always be added later.

Let's start off by assuming we purchase a basic automatic titrator for $8,500.00  

Next, let's examine our most required consumable.  Silver Nitrate- AgNO3.

We performed a salt titration on this food product (soy sauce).  On the label, we can see that the amount of sodium is 590mg of sodium per serving.  For this titration (see below), you can see we used 15.8ml of silver nitrate @ (0.1N mol).   

Note that silver nitrate can come in different strengths so there is a little math we need to consider when deciding on which strength of silver nitrate we should use.

Let's consider using a different strength silver nitrate.  Let's look at using 0.5N mol instead of the 0.1N mol we used in our test.  Initially, we used 0.1N for our titration.  So dividing 15.8mL by 5 helps us see that using a bit stronger silver nitrate will reduce our consumption of silver nitrate.  In this case,  around 3mL per test.   But it's not that simple.  Conversely, we can change the strength of the silver nitrate and make it stronger as long as you don't have other samples that have a lot less sodium.  Otherwise, it would be too strong for the other samples with less sodium and it would not be ideal in those situations (You probably would not find the endpoint).  Bottom line, if you are working with only one burette (doses the silver nitrate), then you are going to need to pick a silver nitrate strength that can be used for all of your samples.  The only alternative would be to refill the burette each time with different strength silver nitrate, or, have a swappable burette on hand.  Having a swappable burette means you can have preloaded burettes with different strength silver nitrate and you can then easily swap them on and off the titrator when needed.  Even better, some titrators can be configured to have two or more onboard burettes which would alleviate the need for manually swapping burettes. 

Let's ignore this for the moment and continue to focus on our cost analysis assuming a single burette.

To give you an idea about pricing for silver nitrate. 

•  We recently purchased some 0.1N mol Silver Nitrate (strength).  A 1 Liter bottle cost approximately $75.00.  Divide $75.00 by 1,000 and the per mL cost is $0.075 per mL of 0.1N mol silver nitrate.   Assume 15.8mL of 0.1N mol silver nitrate per test => 15.8x$0.075=$1.19 per test.

• Assume 0.5N mol Silver Nitrate (strength). => 15.8mL divided by 5 = 3.2mL of silver nitrate per test. (e.g. you will use less with stronger).  Some recent pricing for 0.5N mol; $170.00 / 500mL => $0.34 per mL, or Bulk pricing if you buy a larger bottle $1,000.00 / 4L (4,000mL) => $0.25 per mL ~ 3.2mL per test x $0.34 per mL = $1.09 per test or 3.2mL x $.25 per mL = $0.80 per test.

So if you can purchase silver nitrate in bulk you can drive down your per test cost.

When you decide to test for salt (NaCl) using a titrator you are going to have that initial outlay to pay for the titrator.  After that, it's really a question of what strength of silver nitrate you are using and the amount you are using.   Hopefully, from this example, you can see how the price per test can range from about $0.80 per test to almost $1.20 per test.  So if we do some estimating you could say on average it costs about $1.00 per test.  If you are testing 200 samples per day your daily cost for silver nitrate will cost you about $200.00.

Now let's assume depreciation of the titrator using the straight-line method with the useful life of the titrator equal to 5 years (I think this is what a tax accountant would assume for tax purposes).  $8,500 / 5 = $1,700.00 per year.  Let's assume 251 working days per year ==> $1,700 / 251 = $6.73 per working day in depreciation expense.  In this case, divide that by 200 tests today, and that = $0.03 per test.  

I think these numbers (for the most part) provide a good working basis for determining daily operating costs.  They're probably not perfect but they show you how to go about figuring this out. As always we hope you find this information helpful!