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

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!” 

 

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?  
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?

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:

   
In 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 electrode 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.

Du Nouy Ring Repair Service

Hi, this is Hank Levi, and I wanted to take a minute to tell you about what we're doing to provide repair service and replacement of new Du Nouy Rings.  We have been supporting operators working with popular manual and automatic tensiometers for about 10 years.  It may have been a result of the day-in and day-out working with these tensiometers that led us to where we are today...but it all started about 3 1/2 years ago when we started repairing Du Nouy Rings as part of our service.  About a year later we began providing New replacement Du Nouy Rings also.

Since then we have found customers who have needed help with Du Nouy Rings from other tensiometer manufacturers as well.  Last year Fisher Scientific stopped selling and servicing their tensiometers and with it their ability to provide Du Nouy Ring service.  We also discovered that customers of other manufacturers including Kruss, KSV, Kyowa, CSC, SEO and a few others might have a need for our du Nouy Ring service support too.

Well, the good news is that we are in the Du Nouy Ring business.  We can repair or provide replacement rings for any brand of Du Nouy Ring on the market.  This includes Du Nouy Rings for the popular Fischer Scientific Tensiomat, CSC Scientific, Kruss, KSV, Kyowa, SEO and more.

Do you have a need to have a ring repaired?  Or maybe you just need a new one.  Or maybe both.  Well we can help.  Just submit your contact information so we have a way to reach you and tell us what type rings you have.   We'll have someone contact you to review the details and if needed arrange to have your damaged rings sent in for service.
If you know of another person or organization that could benefit from our service please don't hesitate to forward this information to them.

Surface Tension Measurement with the 70545000 Tensiometer

Have you ever wondered about how surface tension is measured?  Without getting into the details relating to things like, "What's a dyne per centimeter?", "Du Nouy Ring vs. Wilhelmy Plate", "the effects and force of gravity", "viscosity of liquid", or "temperature",  we decided to put together this short video tutorial to help explain the main components of a popular manual tensiometer (70545000) and how the instrument works.  We think seeing how a basic manual tensiometer measures surface tension is helpful in gaining a better understanding of the big picture.

CSC Tensiometer Model 70545 Interfacial from Scientificgear on Vimeo.

 

SOME QUICK FACTS ABOUT SURFACE TENSION AND HOW TENSIOMETERS HELP

APPLICATIONS OF SURFACE AND INTERFACIAL TENSIONS: Surface and Interfacial tension measurements are extremely important in the control and improvement of:

• absorption
• emulsification
• osmotic pressure
• cataphoresis
• evaporation
• solubility
• condenstion
• miscibility

Industries using dye solutions, producing detergents, clarifying liquids, or sparating ores by the flotation process can obtain greater uniformity and efficiency through close control of surface tension of the process liquid.  A close relationship exists between interfacial tensions of oil-liquid systems and the lubricating value of the oil.  Another major use is determining the sludging condition within a transformer, thereby eliminating costly repairs.

 

 

Tensiometer Calibration

Although the CSC Scientific Interfacial Tensiometer is fundamentally very straight forward, it is helpful to have a basic understanding of the operational features and components of the tensiometer.  There are dials, clamps, Du Nouy Rings, and Verniers to consider. 

In this video we show you how to check your calibration using a given weight. 

To conduct this calibration check we assume the tensiometer's tension wire is secure and the unit has the ability to provide a stable reading for your given samples.  Take a look at this short video and let us know if you have questions about the process.

 

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

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.

 

 

 

 

 

Karl Fischer Titrator not finding all of the moisture you expected?

If your operating a dual-reagent Karl Fisher Titrator and your getting lower than expected moisture results you may want to check a few things.  First, make sure your analytical balance or specific gravity (if you use it) calculation is not the problem. Next, focus your attention on the reagents.

Reagents can cause problems if they are not being replaced often enough.

With a dual-reagent setup the operator places anolyte into the main vessel (75mL to 150mL of anolyte solution depending on the vessel size) and catholyte into the generator electrode (5mL of catholyte solution).

Now for some reason, most operators focus their attention primarily on the anolyte reagent and take great care in monitoring the condition and level of the anolyte. Unfortunately their is a tendency to forget about the catholyte. I say unfortunately because it is this oversight that can cause the problem.

Before I tell you the reason for the problem it’s helpful to know some useful information about the reagents ability to measure moisture. A typical vessel can hold 100mL of anolyte. 100mL of anolyte (Coulomat A, Coulomat AG, Coulomat AG-H) can measure 1,000,000 micro grams of water. Yes, 1 million micrograms of water!. Conversely, the pre-measured 5mL ampules of catholyte solution (Coulomat CG) that goes into the generator electrode has the ability to only measure 300,000 micro grams of water per 5mL charge. Do you see it?  Do you see the connection?

There is a 3 to 1 relationship of the cathoyte to anolyte!

Yes, you should be replacing the catholyte 3 times per 1 charge of the vessel. Or put another way, change the catholyte 3 times as often as you change the anolyte.

Now, back to the problem and the answer. If your not replacing the catholyte often enough, the catholyte will actually begin to convert and form a salt by-product. This “salt by-product” can then form and become deposited down around the frit at the bottom of the generator electrode (AKA inner buret) and clog the receptors. When this happens the generator electrode does not work as effectively and can contribute to low recovery on expected moisture levels.

What's the fix?

1. Make sure to change the catholyte more often as required.
2. Soak your generator electrode in methanol or even a light acid over night to clean out some of those salty deposits. That should help.

In these last two pictures we show a Karl Fischer Vessel with a Single-Reagent Generator Electrode inside. Notice how there in no frit at the bottom? -All you see is the platinum screen. In the other picture you can see the bottom of a Dual-Reagent Generator Electrode.  See the white wafer?  This is where the deposit build-up occurs.  Just thought it would be helpful to show both and the differences.

(Note: Coulomat AK anolyte and Coulomat CG-K catholyte are used in combination for samples with Keytones and have a 1 to 1 relationship and can measure 100,000 micrograms of water. Also, the popular Coulomat Oil anolyte has a smaller amount of moisture measuring capability as compared with the other mentioned anolytes above and has a capacity to measure 300,000 micrograms of moisture. eg. If your using Coulomat oil anolyte and Coulomat CG both have the capacity to measure 300,000 micro grams of water and have a 1 to 1 relationship.)

Hope this helps.

How to use a titrator to measure % sodium chloride in food products

Titration

So you need to measure the amount of sodium chloride in your food products. While we have written about this topic previously in other posts and addressed some of the approaches used to test for % sodium chloride (including the use of hand-held salt meters) we have found that it is a more common practice to use an automatic titrator to accomplish this task.  In fact we think it is the preferred instrument and method of choice.  To be sure there are pros and cons to using different methods but we still find that titration is accepted as the primary method for getting the most accurate results.

 

How it's used

Although salt meters using the conductive method are faster (3 seconds vs. 2 to 3 mintues) and can be employed quickly in a production line process, titrators can also be implemented in the same testing environment with modest effort.  Additionally and regardless of how the tests were performed on the production line, titrators are generally put to work in the Quality Control/Quality Assurance Lab as a final check against periodic production line testing.

Supporting the use of titration as an accepted method includes some well known documented techniques including Mohr's and Volhard's methods making titration a recognized and trusted approach.

 

What's next...

Once you have made the decsion to use titration as the testing method it's just a matter of knowing:

• What items you need

• How to prep your sample

• How to setup the titrator

Luckily we have already thought about this and put together a list of 8 items your going to need.  We also created an application-note providing step-by-step instructions for you to follow to conduct a titration.

                                 

                                          

 

                                          

How to test for Salt during food production

Many companies produce the foods we eat.  Do you ever wonder why or how they test for salt during the production process?

Examples by Manufacturing Type

Frozen Vegetable Processor	The salt content of the blanching water is important for maintaining the bright colors of vegetables
A Condiment Manufacturer	Testing Sauces and dressings
A Cheese Maker	Measure the salinity of saltwater that the cheese is soaked in
A Potato Chips Manufacturer	Checking for salt sprinkled on fried potato slices
A fresh Cut Fruit Processor	Use a 2% saline solution with a small amount of ascorbic acid to prevent discoloration of fruits
A Deli Food Supplier	Measure foods with a salt meter vs. by taste
A Canned Food Manufacturing Plant	Measure the brine for canned tuna
A Pickles Manufacturer	Measure the salinity of the brine for salt-packed products
A Cold Cut Meat Manufacturer	Measure salt concentration of ham and deli slices
A Baker	Measure and monitor the salinity of bread dough to around 1%-2%

 

 

 

Salt which is made up of 40% sodium and 60% Chloride is an important ingredient found in food.  While salt can make food taste better, control color, and maintain food texture, it is also considered a health-risk factor (mostly due to the sodium).  Measuring and controlling the levels of salt between the extremes is a constant battle.  Producers of processed foods generally have the biggest need for identifying and controlling salt levels to address not only the taste, color, and texture of foods but also to address some of the healthier eating lifestyles more and more consumers are demanding.

For these reasons it is paramount that salt is measured accurately.  So how do we do that?

Food comes in a variety of forms.  Solid, Liquids, pastes, creams, pieces, chunks, wafers, crackers, gooey, sauces, liquids with chunks in them...let's see what else..Anyway, you get the idea.  There are a lot of ways food can be produced and consumed!

So what device or devices can we use to measure the salt found in these numerous forms of processed foods?

Well, there are a number of "salt meters" out there that can measure salt.  However, not all salt meters can measure the particular salt you are looking for in the same way.  In fact some "salt meters" can only measure salt under certain conditions and or in certain substances like water or sea water.  For this reason it is important to first consider what your going to be testing.  For example, If your food sample includes "food stuff particles" that you can grind into a paste form, then you can probably use a salt meter that utilizes the conductivity method.  On the other hand if you have a brine that you immerse food into and your only concerned with the liquid then perhaps a different salt meter will work.  

The point is this.  The form of the food at the instant you are going to perform the test is key.  Many types of foods can be formed into pastes and diluted with water.  If the food you need to test is like this then a simple salt meter utilizing the conductivity method may be able to perform the test to your satisfaction.  I say may because % salt levels and other accuracy factors may require that you use an entirely different method of titration known as silver nitrate titration instead.

Salt Meter vs. Titration?

              

A brief explanation and description of the two measurement approaches:

The Mohr method, also known as a silver nitrate titration method, utilizes the characteristics of silver nitrate that reacts with chloride ions to measure the salinity %. 

Conversley, some of the more popular salt meters emloy the electric conductivity method.  Both methods measure the salinity but operate on different measurement principles.  However, by creating a conversion table between the two testing methods, correlation between the set of results can be seen.

 

Aside from the measurement capabilities of each approach there are pros and cons to each.

 

 Pro's and Con's

	Salt Meter	Titration
Measurement Range	Less..maybe	More
Accuracy	Less	More
Ease of Use	More	Less
Time to test	Less	More
Cost	Less	More

 

 

 

 

 

 

 

 

 

 

 

 

 

While each method has benefits we have recently found through some informal surveying that some food processors are choosing to use both methods.  These companies are finding that it is easier to use the hand held devices and perform quick spot checks on the production line.  If any problems are identified on the production line then further verification and testing can be performed using the titration approach.  Some think using this collaborative approach is ideal.

 

 

How Much Does a Tensiometer Cost?

 

Tensiometers are instruments used for conducting surface analysis on liquid substances.  Typical applications Tensiometers perform include measuring surface tension, interfacial tension as well as liquid density and Lamella Length on some Tensiometer models.  Some models can also perform other tasks including powder wettability and dynamic contact angle of a solid substrate.  Depending on the types of information the operator is seeking to find one model may be more appropriate than the other.

 

To help prospective users evaluate and compare the different types of models available in the market we have prepared a reference document we call the:

 

"Tensiometer Selection Matrix"

 

This matrix is not necessarily brand specific as it was designed to help those seeking to compare capabilities and prices among popular manual Tensiometer models vs. popular Automatic or "digital" Tensiometer models.

 

We hope you find the Tensiometer Selection Matrix helpful in your search and evaluation of Tensiometers.

 

Can a Karl Fischer Titrator measure moisture in a solid sample?

YES IT CAN!

You can measure moisture in solid samples including plastics, powders, ores, gooey substances that are thick and viscous, greases, and many more.  The key is sample preparation to ensure that a uniform material will be tested.  Once those details are worked out the pattern for testing is the same every time. 

You hear a lot about people running traditional Karl Fischer titration using direct injection with a syringe and needle. That’s pretty easy. 

 

So how do you test for moisture in solids?

For more awkward samples like a solid or solid-like substance we can evaluate the moisture using a Karl Fischer Titrator with an Evaporator Oven.

Believe it or not that’s pretty easy too. I guess that’s why we wrote this post. We wanted to let readers know that the process for running a Karl Fischer moisture test using an evaporator oven is not that difficult.  As mentioned already the most difficult part is probably working with your sample. To help show how the process works we created this short 7 minute video detailing the steps along the way. Please make note that the instruments used for this demonstration are the Karl Fischer Titrator (MKC-610DT) and the Evaporator Oven (ADP-611).

Hope you enjoy.