Meaning
Quantitative chemical solution formulated for moisture determination reacts selectively with water through the reduction of iodine by sulfur dioxide in the presence of an organic base and alcohol solvent. The functional formulation, known as Karl Fischer reagent, provides the analytical foundation for measuring trace water in technical polymers prior to melt processing. Applicability extends to free and bound moisture in engineering resins, ending where insoluble surface additives chemically consume iodine independently of water content.
Chemical Composition
Coulometric and volumetric formulations utilize specialized sulfur compounds dissolved in methanol or imidazoles to maintain rapid reaction kinetics. Absorbed atmospheric moisture degrades unsealed Karl Fischer reagent over time, depleting active iodine concentrations and causing delayed titration end-points. Automated solvent handling prevents ambient humidity from entering the titration vessel during routine analysis.
Titration Stoichiometry
Exact stoichiometric balance requires one mole of iodine for every mole of water present in the dissolved polymer sample. Degradation of Karl Fischer reagent shifts calibration factors, leading laboratory technicians to miscalculate resin dryness and authorize damp resin lots for production. Standardizing reagents against water standards daily maintains quantitative accuracy.
Shelf Decay
Reagent degradation accelerates when storage containers remain open or experience ambient temperature swings. Expired Karl Fischer reagent causes erratic drift values, rendering low moisture measurements in hydrophobic polymers unreliable.
