New Approaches to Moisture Determination in Complex Matrices based on the Karl Fischer Reaction in Methanolic and Non-Alcoholic Media

Moisture determination is of great importance in the production and use of many substances. For example, the moisture content can affect the efficiency of a chemical reaction or determine the shelf life of pharmaceuticals or foods. The standard method for moisture determination is Karl Fischer (KF) titration, based on either volumetry or coulometry. This thesis concerns new approaches to trace determination in complex sample matrices and is focused on oils and substances that interfere with alcoholic KF reagents. Moisture is frequently separated from oil matrices before titration by means of evaporation techniques. In connection with the preparation of new reference materials for moisture in oil, the National Institute of Standards and Technology (NIST) questioned the efficiency of such evaporation techniques. NIST claimed that some of the moisture was sequestered in the oil phase and that it could only be released and detected by using a modified volumetric KF method with a reagent containing at least 65% chloroform. In this thesis, an alternative KF method that meets the proposed requirement for a complete dissolution of the oil sample is presented. With this method it is shown that there is no reason to question the efficiency of the evaporation techniques and that the criticized volumetric method used by NIST is biased high. Ever since its introduction diaphragm-free coulometry has gained popularity due to its ease of use, with a single reagent and short conditioning times. Trace determination with this technique sets great demands on the reagent due to the resulting low current densities at the generator cathode. The performance of several commercial reagents is evaluated under such unfavorable conditions and critical titration parameters are identified. It is also shown that decanol has a favorable effect on the cathode process when using reagents modified with xylene according to standard methods for moisture determination in oils. For samples that are incompatible with the alcohol component in ordinary KF reagent a new reagent based on N-methylformamide is presented. It is shown that is works well for determinations of moisture in a conductive salt used in lithium-ion batteries. The concept of alcohol-free KF reagents is taken a step further in a systematic investigation, also including formamide and dimethylformamide. Advantages and disadvantages with these solvents are discussed and possible reaction paths are surveyed. It is shown that the position of the sulfur dioxide/hydrogen sulfite equilibrium is the main explanation for the large differences in the KF reaction rates in these solvents.