Stoichiometry and chemical metrology: Karl Fischer reaction

Abstract

Stoichiometry of analytical reactions is discussed as an important element of many primary methods (gravimetry, volumetry, spectrophotometry, etc.) and therefore, of chemical metrology as a whole. Variations in stoichiometry caused by non-equilibrium conditions, by changes in the reaction medium or by other factors can be a source of the dominant uncertainty component in the analytical measurement. Such a situation is illustrated with the Karl Fischer (KF) reaction which is widely used in aquametry. Two kinds of solvents used as a part of the reaction medium -alcohols and amidesare compared. The influence of the media on the stoichiometry of the reaction and, correspondingly, on the titre of the KF reagent is evaluated.

Correlation of test results and influence of a mass balance constraint on risks in conformity assessment of a substance or material

“…However, test results of chemical compositions of different batches, lots or objects are inevitably correlated when their actual ("true") values are correlated. Correlations of contents of sample components can be caused by natural physicochemical properties of substances, such as stoichiometry [10][11][12], and by technological reasons in a material production [13,14]. These correlations are taken into account using "conventional" multivariate statistical methods.…”

Application of Karl Fischer's Method to Materials that Only Release Water at High Temperatures

“…The chemical equation that describes the reaction in the coulometric cell is [3]: h + S02 + 3 RN + CH3OH + H20 -* 2 RNHI + RNSO4CH3 (1) where R is an alquil, cicloalquil, aril or acil function of the solvent.…”