How to Clean Karl Fischer Titrator Electrodes

By Hank Levi on Wed, Mar 30, 2016 @ 03:31 PM

How to Clean Karl Fischer Electrodes:

A Karl Fischer Titrator uses two electrodes.  The Inner burette (aka Generator Electrode) and the Detector Electrode.  We hope this infromation is helpful in giving some guidance on cleaing and caring for these Karl Fischer Titrator electrodes.

 

Twin platinum reference "Karl Fischer Detector Electrode" K103-M713/ K103-M714 or any other model

If the electrode is heavily stained and the potential is unstable and measurement reading fluctuates clean with nitric acid. After cleaning use methanol and wipe off with clean gauze.

Cleanelectrode.png

Single or Dual Inner burette K443-0006/ K103-0002 or any other model (aka Generator Electrode)

Periodic cleaning of the inner burette is recommended if the inner burette is stained and the electrolysis reaction will not run smoothly.  A faulty Inner Burette may cause a longer length of time in the measuring process with measurement results being recorded at higher than theoretical values.

 

Cleaning with alcohol: general method

  1. Turn off all power
  2. Disconnect the electrodes from their ports.
  3. Take out both anolyte and catholyte.
  4. Wipe off grease around sliding area with methanol.
  5. Rinse the inner burette with methanol, and fill it with approximately 10mL of methanol and then put it in a beaker. Fill the beaker with methanol up to the level of methanol inside the inner burette, and leave it for about 30 minutes.
  6. After the above 5), dry the inner burette.

 

Cleaning with nitric acid (boiling): If the color of inner burette or diaphragm does not disappear

When there is a deposition of iodine on the diaphragm or the electrode surface, clean with 1mol nitric acid (boiling):

  1. Immerse the diaphragm or the electrode surface in nitric acid, and boil with a hot stirrer.
  2. Drain out the chromate inside the cell, and rinse it with pure water for 2 to 3 times until yellowish color disappears.
  3. Clean the inner burette with methanol or with alcohol.
  4. Repeat the above steps several times when dirt does not come off.

nictricacidwarning.png

 

Cleaning with chromic acid mixture : When dirt does not come off

If foreign objects are observed on diaphragm and platinum surface, use chromic acid mixture instead of methanol for cleaning.

Chromic acid mixture:  1.5g approx. potassium dichromate dissolved in 100mL of concentrated sulfuric acid

Chromicacidwarning.png

 

 

 

 

  1. Follow the same steps as above for methanol.
  2. Drain out the chromate inside the cell, and rinse it with pure water for 5 to 6 times until yellowish color disappears.
  3. Clean the inner burette with methanol or with alcohol.

Chromewarning.png

 

How to dry the inner burette and diaphragm

Dry it in a decompression dryer for more than 2 hours.  Below sketch shows an example of commercially sold drying under reduced pressure.

 howtodryinnerburette.png

 

NOTE:  Dry the inner burette itself only after removed from the titration cell in order to avoid possible breakage of inside ceramic diaphragm.

SUGGESTION: Use a hair dryer if a compression dryer is not available. With a hair dryer, dry the inner burette well enough as long as for more than 10 minutes, especially dry the diaphragm until it is really dried. Any residue of moisture will cause high drift level.

CAUTION: Set the temperature of the constant temperature drying oven at 65°C or below.  When drying with a hair dryer, make sure not to overheat its cable and connector. Overheating may result in malfunction.

 

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Electrode Shower Cleaning for Auto Titrator Sample Changers

By Hank Levi on Thu, Feb 25, 2016 @ 12:04 PM


ELECTRODE RINSE WITH SHOWER ACCESSORY:

Sample changers that are connected with automatic titrators generally are there for a reason.  Efficiency. From an operators point of view getting multiple tests done quickly while being able to take on other tasks in the lab is a key productivity booster.  Sample changers offer various sizes ranging from as few as 6 positions for samples up to some of the largest exceeding 50 sample positions.  Sample changers either have rotating carousels or an arm that moves electrodes and nozzles from sample to sample.  Each time a sample test is completed the electrode must be cleaned before moving on to the next test.  Many sample changers offer as standard a dip rinse between sample testing and as the name suggests it's really nothing more then dipping the electrode in clean water or solution.  For some samples this process is sufficent but for others it is not enough to effectively clean the electrode before the next test.  Luckily most manufacturers of sample changers offer additional cleaning power with the use of a shower rinse system.   Below is a video showing how a shower rinse process works.   Water is stored in a container and then is flushd and rinsed in one of the sample positions designated as the cleaning station.  Water is evacuated via tubes to a drain or sink.  


 
 
 
 
 
 
 
 

 

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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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Where can I get an electrode repaired? - Karl Fischer

By Hank Levi on Mon, Aug 08, 2011 @ 11:00 PM

We work with numerous titrator models and Electrode Repairencounter many of the day-to-day problems associated with broken electrodes.  In many instances some of the electrodes are destroyed beyond repair but in other circumstances we find that some are in fact capable of being repaired. 

Most of our success with repairing or refurbishing electrodes is with Karl Fischer Generator Electrodes (also known as Inner Burettes). 

However, we do try to evaluate and determine whether other types of electrodes can be repaired also.  Generally we will ask for a photo or other description of the damaged electrode to determine if a repair is possible.  An example of how we examine a typical Karl Fischer Generator Electrode can be viewed in the following short video.  Take a look and let us know if we can help you.

Created on 08/08/11 at 22:20:44

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