Introduction
This section of our website is intended to answer the most frequently asked questions and to enable you to develop a greater understanding of the coulometric technique in general and our Aquamax KF titrators in particular.
Our specialists and consultants have spent many years on Karl Fischer titrations – let them help you. If you have a sample analysis problem, or if you are not sure if Karl Fischer titration would be suitable, contact us today for free technical and application advice.
Simply click on any of the following questions (Use the BACK button on your browser to select a different question from the menu after viewing):
What is a Karl Fischer titration?
Volumetric or Coulometric – What is the difference?
What is a coulometric Karl Fischer titration?
What are the advantages of Coulometric Karl Fischer?
Does sample pH have an effect?
Must I keep it in a fume cupboard?
Do I need to be a chemist to use one?
What routine maintenance is required? How often do I change the septa or desiccant?
Calibration & overhaul service – is this possible?
Generator electrodes – with or without frit – which is better?
How does the Aquamax deal with interference from ambient humidity?
What spare parts and accessories do you recommend?
How does one transport the Aquamax for field work?
Can I include on-site training with my Aquamax purchase?
Do I need to change the stirrer speed?
Should I turn the unit off when not in use?
How long will the Aquamax KF last?
What are the costs for repairs?
Can I print duplicate copy of the test results?
How do I change time and date on my unit?
Which chemicals should I /shouldn’t I use?
What is maximum oven temperature to dry glassware?
What if I am “on-site” and can’t clean the glassware, what should I do?
How often must I change reagents?
How do I calculate reagent requirements and cost?
How do I know when the chemicals need to be changed?
Can I use an oil evaporator with the Aquamax?
Can KF titration be used for predictive maintenance?
Is KF titration more reliable than the “crackle test” or distillation technique?
Is the syringe that I use important?
Why does the needle have to go into the reagent?
What is the sample injection technique for transformer oil samples?
What results am I looking for when using standards?
Can display show calculated ppm / % water whilst running titration?
Can I enter sample data, e.g. weight, during titration?
What are delay times for? When would I use them?
Can I upgrade my unit to add new features or fix problems?
I need replacement glassware for other manufacturers’ titrator – can you help?
I have a question not listed, where can I get more information?
What is a Karl Fischer titration?
Since publication of his “New method for the determination of water”, the name of Karl Fischer and his titration technique have been recognised throughout the world. The technique is one of the most widely used and reliable methods for the measurement of water content in a large range of samples. Karl Fischer titration is now employed as a standard method in most laboratories and can be subdivided into two main techniques: volumetric titration & coulometric titration. In 1935 the German scientist, Dr. Karl Fischer, developed a titrimetric determination of water content using a reagent which contained iodine, sulphur dioxide, anhydrous pyridine and anhydrous methanol. This volumetric technique involves dissolving a sample in a suitable solvent and adding measured quantities of a reagent containing iodine until an end point is reached. This end point is determined potentiometrically using a platinum electrode. However, even with the automatic or semi-automatic instruments commercially available there are certain problems associated with the technique. These problems can include long analysis time, reagent calibration required, high reagent consumption rate and large sample amount required. In 1959 Meyer & Boyd were first to apply coulometry to the Karl Fischer principle. In this method the sample is introduced into a mixture of pyridine/methanol which contains iodide ions and sulphur dioxide. Using electrolysis, iodine is produced at the anode which then reacts with any water present. The production of iodine is directly proportional to the amount of electricity. According to the stoichiometry of the reaction, 1 mole of iodine will react with 1 mole of water, and combining this with coulometry, 1 milligram of water is equivalent to 10.71 coulombs of electricity. It is therefore possible to directly determine the amount of water present in a sample by measuring the electrolysis current in coulombs. (Coulombs are a measurement of current multiplied by time). The water present in the anode compartment of the titration cell is coulometrically titrated to a predefined end-point at which there is a minute excess of free iodine present.
Volumetric or Coulometric – What is the difference?
Detection system is the same for each method – only difference is the means by which the “active ingredient” (Iodine) is introduced. In the volumetric technique the iodine is introduced via a burette or similar dosing system. In the coulometric technique the iodine is produced in-situ by electrolysis.
Volumetric technique is generally better suited to high water contents and is most widely used in food, agriculture, industries.
Coulometry, being 1000 times more sensitive, is better for low water content determination.
The volumetric technique involves dissolving a sample in a suitable
solvent and adding measured quantities of a reagent containing iodine until an end point is reached. This end point is determined
potentiometrically using a platinum electrode. The iodine concentration of volumetric Karl Fischer reagents must be checked using standards.
In the coulometric technique the required amount of iodine is produced at the anode which then reacts with any water present. The production of iodine is directly proportional to the amount of electricity. No reagent calibration / standardisation is required.
According to the stoichiometry of the reaction, 1 mole of iodine will
react with 1 mole of water, and combining this with coulometry, 1
milligram of water is equivalent to 10.71 coulombs of electricity. It
is therefore possible to directly determine the amount of water present in a sample by measuring the electrolysis current in coulombs.
What is a coulometric Karl Fischer titration?
Karl Fischer titration is simply a means to measure water content of
samples. Modern instruments, such as the Aquamax KF, use the
coulometric principle, whereby the water present in the sample is
coulometrically titrated to a predefined end point at which there is a
minute excess of free iodine present. Stoichiometrically, 1 mole of
water will react with 1 mole of iodine, so that 1 milligram of water is
equivalent to 10.71 coulombs of electricity. Combining the coulometric technique with Karl Fischer titration, Aquamax KF titrators determine the water content of the sample by measuring the amount of electrolysis current necessary to produce the required iodine. This is an absolute technique which does not require calibration of the reagents.
“ACE” control system, (Patent No.GB2370641), the
Aquamax KF automatically selects the appropriate titration speed
dependent upon the amount of water present in the sample. The titration speed is reduced as the end point is
approached, and when the titration is completed the instrument prints out and displays the results.
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What are the advantages of Coulometric Karl Fischer?
Combining coulometry with the Karl Fischer titration can provide many advantages over the volumetric technique. The main benefits that this coulometric technique offers include higher sensitivity, faster titrations, no reagent calibration required and economical operation.
Indeed, unlike volumetric instruments where the solvent mixture is
normally replaced after each titration, coulometers can determine the
water content of multiple samples on one single charge of reagent.
The criteria governing reagent life are threefold:
The physical size of the titration cell usually allows for 50
- 60 ml of sample to be added. Sample volumes of 0.1
- 2.0 ml are typical for most oil and petroleum products therefore the maximum volume of 50-60 ml is not usually a limiting factor.
The second criteria governing reagent lifetime is the total amount of
water that can be analysed before saturation. A standard charge of
100ml anode reagent can usually analyse upto 1 gram of water. Considering that the injected sample volume is normally quite small, and that usually the analysis is for the determination of low levels of water, then this water capacity should not become a limiting factor either.
Similar to all other Karl Fischer reagents, coulometric reagents deteriorate when left out in sunlight and with increases in temperature. Life expectancy for one charge of reagents when left in the titration cell can be 2-3 weeks although this is also dependent on the total amount of sample injected and the amount of water titrated.
What is a coulomb?
Coulombs are a measurement of current multiplied by time.
Does sample pH have an effect?
The optimum pH range for Karl Fischer titrations is 5 – 7. This will allow the reaction to run quickly and stoichiometrically. Acids are produced during the titration of water and these are neutralized by the base present in the coulometric reagent.
What is drift?
The term Drift refers to the background moisture in the titration
vessel. This could be caused by ingress of atmospheric moisture, chemical reactions between different samples or gradual breakdown of the reagents. Vast majority of high drift values are caused by the titration cell walls and generator electrodes not being cleaned and dried sufficiently. The drift value is normally displayed in micrograms of water per minute. This additional count is automatically subtracted and is assumed to be constant for the duration of the titration. For this reason, the rate of change of the drift value is more important than the actual value itself. Although it is possible for the titrator to be used at high drift values, it is advisable to wait until the drift value is below 20 mg/minute, and stable, before commencing, especially for low water content samples in the ppm ranges. The lower, and more stable the drift – the more accurate the result.
Must I keep it in a fume cupboard?
Although it is recommended that reagents are changed either in a fume cupboard or a well ventilated area, for routine operation it is not necessary to keep the titrator in a fume cupboard. The titration vessel design seals the unit from ingress of atmospheric moisture.
Do I need to be a chemist to use one?
Many of the commercially available coulometric Karl Fischer titrators are now becoming so complicated that a considerable skill level is often required. However, the Aquamax KF titrators, although extremely versatile and suitable for laboratory use, have been designed with non-laboratory personnel in mind. Simple single button operation, easy to assemble glassware, pre-mixed reagents, all make these titrators suitable for almost anyone to use.
What routine maintenance is required? How often do I change the septa or desiccant?
Coulometers, such as the Aquamax KF, require very little maintenance. Ideally, the glassware should be cleaned and dried each time the reagents are replaced but this is not always possible. Likewise, the injection septa and possibly the desiccant should be changed periodically. The required frequency depends on the volume of testing. For example, a program running 100 samples per week will spend about 30 minutes per month cleaning the glassware. Otherwise there is very little to be done.
Calibration & overhaul service – is this possible?
In the U.K., G.R. Scientific offer both in-house and on-site calibration / validation services for almost all makes and models of coulometric Karl Fischer titrators. For USA users, Penn Hills Lab Supply offer an in-house service at their premises in Pittsburgh. This service includes complete overhaul / cleaning of the glassware, checking all electronic settings using calibrated equipment and adjusting as required, replacing consumables such as septa, paper rolls, etc, running water standards and providing a comprehensive calibration certificate.
How do I calibrate titrator?
You can check the performance of your titrator by periodically running water standards such as those supplied with Cou-Lo Formula reagents. Although in principle standardisation of a coulometer is not necessary since the water “titrated” is a direct function of the coulombs of electricity consumed, the ASTM methods for measuring water content of crude oil and petroleum products stipulate that the performance of the coulometer be regularly monitored by injecting 10 microlitre of pure water. The suggested interval is after every 10 determinations and the result obtained should be 10,000 +/- 200 microgram. The reagent should be changed if the result is outside these limits.
Generator electrodes – with or without frit – which is better?
Most manufacturers use a similar configuration of titration cell in which the anode and cathode compartments are separated by a frit (diaphragm) and each compartment is charged with different reagents.
Some companies now offer fritless generator electrodes for use with single solution coulometric reagents.
This combination, at first sight, seems to offer several advantages for the operator. There is only the one reagent to be handles, easier to charge and empty the titration vessel. Unfortunately the formulation of single coulometric reagents are not as suitable for oil and petroleum products as the two reagent methodology. Contact G.R. Scientific for full information.
How does the Aquamax deal with interference from ambient humidity?
This problem is effectively minimized through the Aquamax’s unique titration vessel design and patented ACE control system (automatically compensated errors).
What spare parts and accessories do you recommend?
Reagents, sample port septa and desiccant are the only consumables. Septa and desiccant cost very little and are replaced about once or twice per month. It may be helpful to keep a spare set of glassware on hand for breakage replacement.
How does one transport the Aquamax KF for field work?
The Aquamax KF has a built in battery, an in-car power adaptor and an optional carry case is available. Many Aquamax KF users carry their unit for use on the tailgate of a truck. The carry case also has a compartment for carrying the power pack, syringes, etc. Can I include on-site training with my Aquamax KF purchase? Although the Aquamax KF is simple to setup and operate, some customers choose to arrange for installation and training assistance. Our field specialists can help create a simple and efficient moisture testing program. Training of personnel includes instrument setup, theory, operation, maintenance and performance verification techniques.
Can I include on-site training with my Aquamax KF purchase?
Although the Aquamax KF is simple to setup and operate, some customers choose to arrange for installation and training assistance. Our field specialists can help create a simple and efficient moisture testing program. Training of personnel includes instrument setup, theory, operation, maintenance and performance verification techniques.
Do I need to change the stirrer speed?
The toggle switch on front of the Aquamax KF enables stirrer speed to be adjusted. However, the speed that it starts at when first switched on is an optimum default value which we have found to be suitable for virtually all sample types. It should not be necessary for operator to change this setting.
Should I turn the unit off when not in use?
It is not necessary to switch the unit off overnight but, if it is not going to be used for several days then we suggest that it is switched off. If it is not going to be used for two or three weeks then we suggest emptying the titration vessel, cleaning and drying it and assembling without replacing the reagents. On the day that you wish to start using titrator again you can simply add the new reagent and allow it to stabilise.
How long will the Aquamax KF last?
Most coulometric Karl Fischer titrator manufacturers only provide a 1 or 2 year warranty. At G.R. Scientific we are extremely proud of our manufacturing quality and workmanship, so much so that we now provide a full 5 years parts and labour warranty totally free of charge. A warranty certificate is enclosed with each Aquamax KF titrator.
What are the costs for repairs?
With proper maintenance and careful handling of the glassware, repairs are rarely necessary. Electronic and software failure occurs in less than one instrument per 1000.
Can I print duplicate copy of the test results?
If you are out “on-site” and wish to leave a hard print copy of results with your customer whilst also bringing original hard copy back to your depot, simple hold down the Start key for three seconds and a duplicate print will be made.
How do I change time and date on my unit?
This is extract from the Aquamax KF user manual;
SETTING THE DATE AND TIME
1. Switch on the Aquamax KF and wait for it to display the following:
2. Hold down the 
key until the Aquamax KF displays:-
3. Use the 
decimal point key to move the cursor across the screen.
4. Use the numerical keys to set / alter the required number
5. When completed press the key to save the changes and exit.
How do I clean theglassware? Which chemicals should I / shouldn’t I use?
Under normal circumstances the titration cell can be used for a large number of samples before having to replenish the reagents. Once the reagents have been exhausted, or when the titration cell maximum volume has been reached, it should simply be necessary to:-
1. DISASSEMBLE titration cell (disconnect leads from titrator)
2. EMPTY the titration cell and generator electrode
3. RINSE all parts with methanol. Do not use brush on electrodes.
4. DRY all parts
5. REASSEMBLE glassware
6. RECHARGE with fresh reagents
If the cell is heavily contaminated then it may be necessary to clean it more thoroughly. For oil samples, cleaning with chloroform or xylene is suggested, whilst for salt deposits a water wash may be required. Use whichever solvent is most suited for the sample type. The titration vessel (not the electrodes) can even be cleaned with hot soapy water and a bottle-brush. However, after cleaning with suitable solvent, all glassware parts, should be rinsed inside and out with methanol. They can then be dried with a warm air blower, such as a domestic hair dryer, placed in a low temperature oven at 40 – 50 °C, or left in a desiccator.
After being fully dried, reassemble the titration cell and charge with fresh reagents.
THE MORE THOROUGHLY THAT THE TITRATION CELL IS CLEANED AND DRIED, THE FASTER THE INSTRUMENT WILL STABILISE READY FOR OPERATION AFTER RECHARGING REAGENTS.
Under normal conditions, the Aquamax KF should be ready for operation within 5 – 10 minutes after reassembly, however it could take considerably longer to completely stabilise if the drying procedure has not been properly carried out.
What is maximum oven temperature to dry glassware?
After cleaning the glassware with suitable solvent, all glassware parts, should be rinsed inside and out with methanol. They can then be dried with a warm air blower, such as a domestic hair dryer, placed in a low temperature oven at 40– 50 ° C, or left in a desiccator.
What if I am “on-site” and can’t clean the glassware, what should I do?
Although it is highly recommended that the glassware be cleaned and dried before replacing reagents, it is not always possible to achieve this, especially when away from the laboratory or workshop. In these circumstances we suggest emptying the reagents into a suitable container and re-assembling the glassware as quickly as possible. The least time that the generator electrode is exposed to atmospheric moisture then the faster the titration vessel will stabilise again after replacing reagents.
Which reagents should I use?
“Cou-Lo Formula” reagents offer optimum performance with almost all models of coulometric Karl Fischer titrators. Our packaging concept has been based on advice from the HSE (Health & Safety Executive) to enable non-laboratory personnel to work more safely.
Cou-Lo Formula “A” anode reagents is suitable for most routine applications and is especially useful for water content
determination of oil samples.
The anode reagent, which contains the required amount of xylene and other solubilizers, is supplied in 100ml “single
shot” bottles, no volume measurement or mixing with other solvents is required. The cathode reagent, Formula “C”, is supplied in “single shot” 5ml ampoules which have “safety snappers” pre-fitted thereby educing risk to the operator. Each pack contains 8 x 100ml bottles of anode reagent plus 8 x 5ml ampoules of cathode reagent plus two water standards. Weighing only 3 kilo, the total pack volume is less than one litre so they can be shipped as limited quantity.
How do I change the reagents?
This is extract from the Aquamax KF user manual;
For most routine applications 100ml of Formula “A” (anode reagent) and 5ml of Formula “C” (cathode reagent) are used. When analysing Transformer oils, Crude oils and other petroleum products Formula “A” is especially suited as it contains other solvents to improve sample miscibility and solubility.
(When analysing samples of Ketones, amines or others which may interfere with the reaction it is advisable to use specialised reagents which can be obtained from various suppliers).
 |
Although reagents can be poured into the titration vessel whilst it is located on the titrator, we recommend that the vessel and electrodes are removed from the instrument whilst this procedure is performed to avoid reagent spillage onto the instrument casing. (Any spillage onto the instrument casing should be wiped off immediately to avoid damage or staining). |
 |
Remove the drying tube and injection septa. Using the funnel supplied, charge the titration vessel upto the lower line with Formula “A” reagent. For your convenience these reagents are supplied in “single shot” bottles which contain 100ml so it is not necessary to measure any volumes – simply pour in the complete bottle |
 |
Also using the funnel, charge the inner chamber of the generator electrode with Formula “C” reagent which are supplied in “single shot” 5 ml vials which have “safety snappers” pre-fitted thereby reducing risk to the operator.(It is not necessary to clean the funnel between reagents.) |
 |
Reconnect the drying tube and injection septa so that the titration vessel is sealed from ingress of atmospheric moisture.Locate the complete titration vessel onto the titrator and connect the electrode leads onto the appropriate sockets |
How often must I change reagents?
How do I calculate reagent requirements and cost?
How do I know when the chemicals need to be changed?
Are all reagents the same?
Are reagents dangerous?
Coulometric reagents are generally classed as hazardous and / or toxic. Each pack of Cou-Lo Formula reagents contains MSDS data sheet and copies of these can also be downloaded from the G.R. Scientific website.
Can I use an oil evaporator with the Aquamax?
Some oils contain additives that can interfere with water measurements and therefore require a secondary technique employing an evaporator. Most commercially available evaporators can be easily interfaced with the Aquamax KF.
Can KF titration be used for predictive maintenance?
Water, acid and fine particulates in EHC (electrohydraulic control) fluids are the primary causes of failures. Water is the simplest of these to measure. Monitoring water content can provide major financial savings in fluid replacement and equipment failure.
Is KF titration more reliable than the “crackle test”
or distillation technique?
Both of these techniques are semi-quantitative at best and are sensitive to only large amounts of water. The Aquamax KF is reliable and accurate down to 1 ppm of water.
Is the syringe that I use important?
If samples are being analysed by W/w then the accuracy of the syringe is less important. However, if analysing by V/SG method, whereby a measured volume of sample is injected into the titration vessel, then the syringe and syringe technique of the operator, are of great importance. A good quality gas tight syringe with luer lock needle is recommended.
Why does the needle have to go into the reagent?
For samples such as transformer /insulating oils, which are viscous and contain low levels of moisture, we recommend inserting the syringe needle below the surface of the anode reagent before injecting the sample. This ensures that the sample is given enough time to disperse in the reagent and for the detector electrode to see any signal change. Please remember that no titration takes place until after the detector electrode has seen a signal change caused by the presence of water.
What is the sample injection technique for transformer oil samples?
This is extract from the Aquamax KF user manual;
Program the Aquamax KF with parameters for the analysis. For Transformer Oil samples, these parameters are usually:-
Result Format = mg/kg or ppm
Calculation Mode = V/SG
Sample Volume = 1.0 ml
Sample SG = 0.875
ANALYSIS METHOD
1. Confirm that Aquamax KF is in “Ready” mode
2. Flush 1.0ml syringe several times (minimum 6 times) with sample
3. Fit luer needle and flush through with sample
4. Draw sample into syringe beyond the 1.0ml marking
5. Invert syringe so that any air bubbles can be ejected through the needle and adjust syringe plunger to the 1.0 ml mark
6. Wipe off excess sample from outside of needle using a clean, dry tissue or paper towel
7. Pierce needle through injection septa of titration vessel (1 – 2 cm)
8. Press START
9. Push needle into anode reagent and inject sample
10. Withdraw needle from titration vessel
11. Read result, in mg/kg (ppm) water, on display and printout
12. Repeat steps 2 – 11 if duplicate result required
What results am I looking for when using standards?
There are various commercial water standards available, including our own Cou-Lo Formula standards. Some standards provide results as water content by weight, others by volume. As many Aquamax KF users require on-site operation of the titrator they do not always have a balance available. As such we decided to provide water standards based on 0.1 milligram per millilitre and 1.0 milligram per millilitre. This means that the operator, even when out from the laboratory, can check that his titrator is operating correctly by simply injecting 1.0 ml of standard which will give results
of 100 or 1000 microgram counts
Can display show calculated ppm / % water whilst running titration?
The Aquamax KF is programmed so that the calculated amount of water (ppm or percentage) can be displayed live during the titration. It is not necessary to wait until the end point has been reached to see if water content is going to be above specification.
Can I enter sample data, e.g. weight, during titration?
The Aquamax KF is programmed so that the sample data required for the calculation can be entered during the titration. This is particularly useful when analysing samples by W/w calculation (Weight) as the Tare weight can be entered whilst titration is still in progress.
What are delay times for? When would I use them?
The Aquamax KF has two different delay times which are operator programmable. Start Delay enables additional time to be added before electrolysis current is applied and the titration starts to count. This is useful if the sample is very viscous or is slow to release water Minimum Titration Time allows the titration to commence and to count as normal but does not enable the end point to be reached until at least the programmed minimum time has elapsed. This is useful when using a vaporiser or sometimes when analysing gas samples which have very low water content.
Can I upgrade my unit to add new features or fix problems?
Older Aquamax KF units can be re-programmed with our latest versions of software for very little cost. Alternatively, we can also offer substantial trade-in discounts if your old titrator, regardless of make or model, is given in part exchange. Contact us for details.
I need replacement glassware for other manufacturers’ titrator – can you help?
Our glassblowers have specialised in manufacturing coulometric Karl Fischer electrodes, vessels, etc, for many years. We can provide equivalent glassware for almost all makes and models of coulometric Karl Fischer units at a very competitive price. Contact us for details
I have a question not listed, where can I get more information?
Our specialists and consultants have spent many years on Karl Fischer titrations – let them help you. Call us at 412-841-6988 or email us at If you have a sample analysis problem, or if you are not sure if Karl Fischer titration would be suitable, contact us for free technical and application advice.