Flow injection turbidimetric determination of thiamine in pharmaceutical formulations using silicotungstic acid as precipitant reagent.

A simple flow injection system is proposed for the determination of thiamine in pharmaceutical formulations. The determination is based on the precipitation reaction of thiamine with silicotungstic acid in acidic medium to form a thiamine silicotungstate suspension that is measured at 420 nm. Adding 0.05% (w/v) poly(ethyleneglycol) in the carrier solution (0.5 mol l(-1) hydrochloric acid), an improvement in the sensitivity, repeatability and baseline stability of the flow injection system was obtained. The calibration graph was linear in the thiamine concentration range from 5.0x10(-5) to 3.0x10(-4) mol l(-1) with a detection limit of 1.0x10(-5) mol l(-1). The relative standard deviations for ten successive measurements of 1.0x10(-4) mol l(-1) and 2.5x10(-4) mol l(-1) thiamine were less than 1% and an analytical frequency of 90 h(-1) was obtained.