Abstract: A new electrochemical method for the on-line determination of vitamin B₁ is presented.Based on dead-stop endpoint biamperometry by using two platinum foil electrodes with an applied potential difference of 150 mV, vitamin B₁ can be oxidized by hexacyanoferrate (Ⅲ) in a sodium hydroxide medium via a reversible indicating couple Fe(CN)₆^4-/Fe(CN)₆^3-.The cell current is linear with the concentration of vitamin B₁ in the concentration range of 4.0×10^-6—1.0 × 10^-3 mol/L with a detection limit of 8.0×10^-7 mol/L(0.27 μg/mL).Most familiar excipients,ions and vitamins do not interfere with the determination of vitamin B₁.The method displays the advantages of simplicity, high efficiency(180 samples/h), and high selectivity, and is suitable for the determination of vitamin B₁ in pharmaceutical preparations.

Key words: Pharmaceutical analysis, Biamperometry, Vitamin B₁, Flow-injection analysis