Karl Fischer Over Titration and 7 things you should know about it

By Hank Levi on Wed, May 02, 2012 @ 06:30 PM

We have all seen it.  We’re running a test to see how much moisture is in our sample when inexplicably the liquid inside the Karl Fischer vessel starts to turn from a normal light-yellow color to a dark burnt-red looking color.  Sometimes the titrator screen will inform us of the problem with a digital readout stating the dreaded

OVER-TITRATION!” 

kfbeforestart resized 600describe the imagedescribe the imagedescribe the image

 

Sometimes the digital readout says nothing at all.  In either case the operator knows something has gone wrong because the Karl Fischer Titrator is no longer giving moisture results.  A panic to figure out the problem and get testing underway again becomes the immediate priority. 

But where do you start?  

As it turns out “over-titration” is probably one of the top 2 or 3 complaints or issues we hear about from operators.    So what is causing this problem to occur?  How can we determine the source of this problem, fix it, and more importantly how can we avoid it?

 
This is a critical question for operators and managers working in a production or QC environment who are concerned with keeping their Karl Fischer Titrator 100% “in-service”, day-in and day-out.   Having the ability to identify the problem correctly so appropriate measures can be taken quickly is very important.

 
So how do we approach the problem of “over-titration”?   By knowing the facts.  Having a clear understanding of the process can help operators correct the problem faster when time is of the essence.  

Important facts you should know about over-titration:  
  1. Over-titration is a state where there is more iodine present in the vessel than water (general definition).
  2. When over-titration occurs the vessel will become very dark as a result of the abundance of iodine present inside the vessel.
  3. The reagent inside the vessel should normally have a light-yellow color absent a very dark sample such as oil.
  4. The Karl Fischer Titrator always attempts to maintain an equilibrium where only enough iodine is introduced to counter and neutralize the water present inside the vessel.
  5. During a single titration test there should only be enough iodine introduced to counter and neutralize the amount of water present inside the titration vessel during that test – no more, no less.
  6. Any incident that interferes with the final amount of iodine introduced during the titration test can lead to dis-equilibrium and result in more iodine being introduced than necessary.
    Important facts you should know about Karl Fischer Titrator Glassware:  
  1. The Karl Fischer Vessel and Glassware is composed of the following
    1. Vessel (coulometric and volumetric)
    2. Generator Electrode (coulometric only) - The Generator Electrode is a precision electrode designed to deliver an electrical current inside the vessel to the reagent – causing the reagent to produce iodine
    3. Titration nozzle (volumetric only) - The titration nozzle delivers precise amounts of iodine (composite or titrant) via a burette driven mechanism using a piston
    4. Detector Electrode (coulometric and volumetric) - The detector electrode has a sole purpose and probably the most important role in continuously monitoring and determining the conductivity levels within the titration vessel.
  So what are the causes that can lead to over-titration? 

✓ A damaged Detector Electrode

✓ A "Tricked" or "Fooled" Detector Electrode (no joke)

 

Since coulometric and volumetric Karl Fischer Titrators handle the delivery of iodine differently it’s worth describing the two methods separately.  

A Word About Coulometric Karl Fischer Titration:

In a coulometric system the reagent is a complete system where it is designed to release iodine when the generator electrode delivers an electrical current to it.  So what causes the generator electrode to deliver too much current causing the over production of iodine?  Another way to say it is, “who or what” is telling the generator electrode to continue to generate a current when it’s not needed?  

   
The detector electrode!  So why would the detector electrode do this?   describe the image
Without getting into too much of the electronics the detector electrode is designed to “detect” conductivity in the vessel.  Depending on the amount of conductivity detected the detector electrode will send a message to the titrator telling it to continue producing a current - enough to release the appropriate amount of iodine to counter and neutralize the water present in the vessel.  As long as this process is working during a titration an eventual endpoint will be found and a result will be produced.  


So it’s really a problem of misinformation. If the Karl Fischer Titrator is not getting the right information from the detector electrode then over-titration is possible. 

The problems we see that can effect the proper functioning of the detector electrode include:  
  1. The electrode cable.  If the cable becomes cracked or breaks it can cause a situation where the message to the titrator is to continue producing a current – continually.  In this case the vessel will become very dark and in most cases the titrator will not even know it is in an over-titration state.  The generator electrode will simply continue to produce a current, turning the vessel very dark.  There will be no other warning or notice from the titrator for the operator to see.
  2. Cracked electrode.  Sometimes mishandling or even a stirrer bar bouncing around inside the vessel can cause a tiny crack near the bottom of the detector electrode that cannot be seen with the naked eye.  These cracks can allow small amounts of reagent inside the electrode enough where errors in detection will begin to occur.  What ensues is an unstable drift that jumps around giving the titrator a misreading. The jumping around and unstable drift may be picked up by the titrator and an error stating “OVER TITRATION” may be seen on the screen of the titrator.
  3. Cable connectors.  Sometimes the connectors on the titrator itself can become dirty, wet and corroded.  Also, some electrodes use multi-plug designs that can also become dirty, wet and corroded.   These connectors if not clean and dry can lead to a similar misreading similar to a cracked electrode where the drift begins to jump around and become unstable.  The titrator may also state that there is “OVER TITRATION” when this occurs.
A "Tricked" or "Fooled" Detector Electrode you say?describe the image

If it’s determined that the problem is not the detector electrode then we need to look at the stirring action inside the vessel.  If the iodine being released is not mixing well because the stirrer is off or set too low, then the detector electrode will not realize there is iodine already released inside the vessel.  This will cause the detector electrode to continue telling the titrator to produce more current via the generator electrode up to the point where the detector electrode senses a reduction in the conductivity level inside the vessel.  Conductivity only reduces as the iodine interacts with the water.  So it is important for the detector electrode to sense the true and most accurate “mix or state” of iodine and water during the titration process.  If it does not know the true state of the mix it will be fooled into telling the titrator to keep going – causing OVER TITRATION.        

A Word About Volumetric Karl Fischer Titration:

   
describe the imageIn a volumetric system the reagent setup is different where a composite or titrant is introduced via a burette piston through a titration nozzle.  The amount of composite or titrant delivered is based upon the commands of the titrator.  The command from the titrator to the burette and piston that push out the “iodine” through the titration nozzle is, yes, given by the detector electrode.  For the purposes of this discussion the difference between the coulometric and volumetric setup is that the delivery of iodine is different.   But the same problem can occur where the iodine does not mix well and therefore trick the detector electrode in to thinking there is not enough iodine present inside the vessel to counter and neutralize the water.  Since both coulometric and volumetric Karl Fischer Titrators use detector electrodes the problems mentioned earlier about the detector electrode will hold true with volumetric titrators also.  

 

 

  7 Thoughts (DOs and DON'Ts) on Problem Solving and Prevention:  

1.  Don’t abuse the detector electrode!  Be very careful with the detector electrode and do not handle it unnecessarily.  Small bumps (clanks) here and there can lead to a crack.   Do you really need to remove the detector thinking dragonelectrode from the vessel all the time?
2.  Don’t turn up the titrator’s stirrer speed to high.  This will only cause the stirrer bar to bounce around uncontrollably and possibly hit and damage the detector electrode (crack).
3.  Do inspect all connections and connectors on the detector electrode cable and Karl Fischer Titrator to ensure they are dry and clean.
4.  Do be careful with the detector electrode cable.  Try not to bend it unnecessarily.
5.  Do make sure there is enough stirring action inside the vessel to mix the iodine around effectively.  A small vortex should be visible.  But not too fast to cause the stir bar to bounce around.
6.  Do introduce some moisture - Sometimes when you are in an over-titration situation and the vessel is already very dark you can introduce a little moisture to bring the vessel back to equilibrium.  This sometimes works and immediately the vessel turns from a dark burnt-red color to a light-yellow.
7.  Do have a spare detector electrode on hand.  This little electrode seems to get over looked but plays a huge role inside the Karl Fischer Titrator vessel.

Created on 05/02/12 at 18:10:44

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What are Karl Fischer Water Standards and what do the numbers mean?

By Hank Levi on Thu, Feb 09, 2012 @ 01:44 PM

Most everyone working with Karl Fischer Titration at some point ends up wanting to check their instrument for accuracy and overall operational readiness.  Karl Fischer Water Standards were made to assist operators with making these operational checks.  Sometimes however we find there is some confusion about the choice of water standards available and what the numbers mean.

Karl Fischer Titration Water Standard Video from Scientificgear on Vimeo.

Hydranal water standards provide a few popular choices for both coulometric and volumetric Karl Fischer Titrators:

  • Hydranal 0.1 (100PPM ±10% error acceptance)
  • Hydranal 1.0 (1,000PPM ±3% error acceptance)
  • Hydranal 10.0 (10,000PPM)

So what do the numbers mean?  0.1, 1.0, 10.0?

Simply put, these numbers tell us the amount of moisture (H2O) that is present in 1 gram of the water standard.  The amount of moisture (H2O) is expressed as milligrams on the packaging.  Using the Hydranal 1.0 for example we say there is 1.0 milligram of moisture (H2O) in 1 gram of the water standard.  Did you know there are 1,000 micrograms per 1.0 milligram?  Yes there is.  So instead of thinking in terms of 1 milligram per 1 gram of water standard, think in terms of 1,000 micrograms per 1 gram of water standard.  Why?

Karl Fischer Titrators count moisture in micrograms!

Since Karl Fischer Titrators count moisture in micrograms it's easier to think about the water standards in terms of micrograms.  Why?

We evaluate our water standard test in PPM

For the Hydyanal 1.0 we are looking for results within ±3% of 1,000PPM (970PPM to 1030PPM).  For the Hydranal 0.1 we are looking for results within ±10% of 100PPM (90PPM to 110PPM).

 

Don't forget this formula!:

PPM = WATER DETECTED IN MICROGRAMS/SAMPLE SIZE IN GRAMS

(For those who don't know PPM stands for Parts Per Million)

We hope this information has been helpful.

 Created on 02/09/12 at 13:36:32

 

 

 

 

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Karl Fischer Titration and Water Standard Presentation

By Hank Levi on Tue, Jun 28, 2011 @ 10:43 AM

Kf waterstandard presentation resized 600In this presentation we discuss the basic Karl Fischer Water Standards and talk about some of their uses for both Coulometric and Volumetric Karl Fischer Titration.  We also describe some of the related problems that can be identified and overcome by using Karl Fischer Water Standards.

  • Karl Fischer Water Standards
  • Why we use them
  • Coulometric Karl Fischer
  • Volumetric Karl Fischer
 

Created on 06/28/11 at 10:48:28
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Karl Fisher Titration and the 20 Most Critical Questions

By Hank Levi on Sun, Jun 12, 2011 @ 12:27 PM

questionsAs a service provider of Karl Fisher testing apparatus, we see different moisture testing issues that many operators, managers, and even companies face. We have come to realize that helping operators become more knowledgeable about "the little things" can help boost confidence, improve performance and efficiency, and ensure accurate testing. 

Are you new to Karl Fisher Titration and just beginning to learn about moisture testing or has it just been a while since you had to pull the Karl Fisher Titrator out to run some tests?  Regardless of your reason we know how important it is to get up to speed quickly so you can be running tests and providing moisture test results to those who need them.

To help with this we have compiled a list of the 20 most critical questions to help operators navigate through the learning curve and gain a better understanding of Karl Fisher Titration.

Some examples of issues you will discover include:

1.  "Our Karl Fisher says 'OVER TITRATION' and the reagent is turning really dark. Why?”

2.  “Why won’t the instrument go into “Ready mode”?”

3.  “Results seem "all over the place", what should I do?”

4.  "We use a solids evaporator and we are getting ZERO moisture results. Why?"

5.  "How many tests can I run and when should I change out my reagents?"

 

Avoid unnecessary surprises by getting a copy of the complete list of questions and learn what the issues are and why they are important.

Created on 06/11/11 at 08:00:22

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Karl Fisher Titration Advantages for measuring moisture

By Hank Levi on Thu, Jun 02, 2011 @ 11:12 AM

Karl FisherThere are multiple methods of moisture determination, including loss on drying, Karl Fischer titration, piezoelectric sorption, spectroscopy, and chilled mirrors among others. However, it is advantageous to use Karl Fischer (KF) titration in moisture analysis for the following reasons:

  • It is highly accurate and precise (Part Per Million Accuracy).
  • KF is specific to water determination. This specification is different from the other popular moisture analysis method, loss on drying (LOD), because LOD can detect the loss of any volatile substance. However, this specification is advantageous because it allows KF titration to work independent from volatile substances present in the sample
  • The process does not require large samples, which is typically truer with Loss on Drying where more sample is required to achieve higher accuracy and repeatability - which introduces another entirely different problem.
  • It does not require much time to perform an analysis since the samples are easy to prepare and the analysis itself is short in duration.
  • The method has a nearly unlimited measurement range (from 1ppm to 100%).
  • Karl Fischer titration can determine the moisture content of a sample in any state, whether it is a solid, liquid, or gas.

We hope the above advantages show some of the benefits that Karl Fischer titrators can provide.  Even today with technological advancements Karl Fisher Titration remains very popular not only because of the advantages we mention, but also because it is widely accepted as a standard for moisture detection and measurement.

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Calibrating Karl Fisher Titrators using water standards

By Hank Levi on Fri, May 20, 2011 @ 02:33 PM

“Calibrating” a Karl Fischer titrator is somewhat of a misnomer.MKC520 Karl Fisher Titrator What most operators are attempting to do is determine whether their Karl Fisher titrator is measuring moisture accurately.

A simple method is to run a water standard through the Karl Fischer Titrator like a normal direct injection test. Depending on the water standard you use, the result should equal a pre-determined level of moisture plus or minus a margin for error. These water standards are certified by the manufacturer (a certificate is included) to equal a precise level of moisture.

We use Hydranal water standards. There are two kinds we typically use for coulometric Karl Fischer Titrators.

1) 0.1 normal

2) 1.0 normal.

The 0.1 normal administered at about 1mL should result in 100ppm (Parts Per Million) of moisture when measured. The acceptable result for this standard for the Karl Fischer titrator is +/- 10%. So your Karl Fischer Titrator should produce a reading between 90ppm and 110ppm to be in the acceptable range. If it is, you know your Karl Fischer Titrator is performing correctly.

For the 1.0 normal everything is the same except the standard should result in 1,000ppm and your acceptable range is smaller at +/-3%. So your Karl Fischer Titrator should produce a reading between 970ppm and 1,030ppm.

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