Flow-injection spectrophotometric determination of vitamin B-1 (thiamine) in multivitamin preparations

A flow-injection (FI) spectrophotometric procedure is proposed for the dete rmination of vitamin B1 (thiamine hydrochloride) in multivitamin preparatio ns. Powdered sample, containing from 25 to 100 mg of multivitamin preparati ons, was previous dissolved in 0.1 mol L-1 hydrochloric acid, and a volume of 250 mu L was injected directly into a carrier stream of 0.10% (w/v) pota ssium hexacyanoferrate(lll) in 0.5 mol L-1 sodium hydroxide at a flow rate of 2.46 mL min(-1) an FI system. The thiochrome produced in the oxidation o f thiamine hydrochloride by potassium hexacyanoferrate(lll) in alkaline sol ution was directly measured at 369 nm. Potassium hexacyanoferrate(lll) in t his concentration did not cause any interference. Vitamin B-1 was determined in three multivitamin preparations in the concen tration range from 2.5 to 50.0 mg L-1 (calibration graph: A = -0.0132 + 0.0 134 C, r = 0.9990, where A is the absorbance and C is the vitamin B-1, conc entration in mg L-1). Sucrose, glucose, fructose, lactose, citric acid, sta rch, vitamin B-2, and vitamin B-6 do not interfere, even in concentrations five times higher than vitamin B-1. Only vitamin B-12 causes interference, but this vitamin is not present in the multivitamin preparations used in th is work. The detection limit was 1.0 mg L-1, and the recovery of vitamin B- 1 from three samples ranged from 97.5 to 105.0. The sampling rate was 41 h( -1) and RSDs were less than 1 % for solutions containing 10.0 and 30.0 mg L -1 vitamin B-1 (n = 10). The results obtained for the determination of vita min B-1 in commercial preparations are in good agreement with those obtaine d by differential pulse polarography (r = 0.9999) and also with the label v alues (r = 0.9998). (C) 1999 John Wiley & Sons, Inc.