Construction of a Pyridine-Free Karl Fischer Reagent for Trace Determination of Water in Non-aqueous Media by Coulometric Detection

Abstract

Laboratory preparation of a pyridine-free Karl Fischer (KF) reagent used in coulometric determination of water was investigated. The prepared reagent consisted of a methanolic solution of an organic base, organic pH buffers, sulfur dioxide and an organoiodide salt. In order to avoid a non-stoichiometric course of KF reaction and prevent the unfavorable influence of by-products produced especially in cathodic compartment, a halogenated hydrocarbon free active halogen was employed in the reagent. This reagent was ideally suited for trace determination of water in solvents, inorganic and organic raw materials, petroleum products and other matrices, which were free from aldehyde, ketone and thiol species. Using masking agents, change of solvent, indirect analysis and other techniques were recommended for removing or minimizing some interferences in measurements. In evaluation of such reagent, various measurement parameters such as pH, end point stability, titration speed, neutralization capacity, accuracy and precision were studied. Also performance and preferences of the reagent in comparison with commercial one and two component reagents were demonstrated. A limit of detection of 0.6 µg g−1 in titration vessel, by using constructed reagent, was obtained and the relative standard deviation obtained from successive measurements (n = 4) at 5 µg g−1 level in samples was 2.5%.