This is a quantitative test which determines the amount of water present in the oil. Water can be present in three forms: dissolved, emulsified, or free. The Karl Fischer Water Titration measures all three. The test is accurate down to the 10 ppm level, and is the only acceptable test for measuring quantities below 500 ppm. This is important when looking at turbine, pump, and compressor oils, which most often have a tolerance level of about 100 ppm. Today this test is most often done on automatic titrators which are extremely sensitive.

A small measured amount of representative sample is introduced in the reaction vessel. This amount is usually 1 cc; however, the analyst will vary this according to how much water is expected. In the reaction vessel, water molecules will react with an iodine solution to form iodate. This iodate will increase the potential at a platinum electrode. The current increase as a result of the potential increase is directly related to the amount of water present. When all the water molecules have been titrated, the potential will return to its normal state. The instrument will analyze the curve created by the current increase vs. time, and calculate the amount of water present. Results are reported in parts per million (ppm).

Advantages

• Even trace amounts of water can be determined.
  
• The test is relatively quick and easy to run on an automatic titrator.
  
• The results are generally repeatable to within 5%.

Disadvantages

• The required reagents are costly.
  
• Certain sulfur compounds have a positive interference on the results.
  

Karl Fischer