Flow-injection spectrophotometric determination of vitamin B1 (thiamine) in multivitamin preparations

A flow-injection (FI) spectrophotometric procedure is proposed for the determination of vitamin B1 (thiamine hydrochloride) in multivitamin preparations. Powdered sample, containing from 25 to 100 mg of multivitamin preparations, was previous dissolved in 0.1 mol L⁻¹ hydrochloric acid, and a volume of 250 μL was injected directly into a carrier stream of 0.10% (w/v) potassium hexacyanoferrate(III) 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 of thiamine hydrochloride by potassium hexacyanoferrate(III) in alkaline solution was directly measured at 369 nm. Potassium hexacyanoferrate(III) in this concentration did not cause any interference.

Vitamin B₁ was determined in three multivitamin preparations in the concentration range from 2.5 to 50.0 mg L⁻¹ (calibration graph: A = −0.0132 + 0.0134 C, r = 0.9990, where A is the absorbance and C is the vitamin B₁ concentration in mg L⁻¹). Sucrose, glucose, fructose, lactose, citric acid, starch, vitamin B₂, and vitamin B₆ do not interfere, even in concentrations five times higher than vitamin B₁. Only vitamin B₁₂ causes interference, but this vitamin is not present in the multivitamin preparations used in this work. The detection limit was 1.0 mg L⁻¹, and the recovery of vitamin B₁ 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 B₁ (n = 10). The results obtained for the determination of vitamin B₁ in commercial preparations are in good agreement with those obtained by differential pulse polarography (r = 0.9999) and also with the label values (r = 0.9998). © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 45–50, 1999