Simple and sensitive normal and reverse flow injection methods for spectrophotometric
determination of thiamine hydrochloride (THC) at the microgram level were proposed and
optimized. Both methods are based on the reaction between THC and diazotized metoclopramide in alkaline medium. Beer’s law was obeyed over the range of 10–300 and 2–90 mg/mL, the limits of detection were 2.118 and 0.839 mg/mL and the sampling rates were 80 and 95 injections per hour for normal and reverse flow injection methods respectively. The application of both methods to commercially available pharmaceuticals produced acceptable results. The flow system is suitable for
application in quality control processes.