Residual thiosulfate determination in omeprazole by liquid chromatography

An HPLC-UV method for the determination of thiosulfate in aqueous media was modified and validated in this study to quantify the amount of residual thiosulfate in omeprazole samples. Absorption of thiosulfate ion was monitored at 215 nm in alcoholic tetrabutylammonium hydroxide solution as a mobile phase, in which the pH was adjusted to 6.20 by using dilute hydrochloric acid. A method detection limit of 0.08 mg/L was achieved for thiosulfate ion in 1000 mg/L omeprazole solution. The precision, accuracy, and the expanded uncertainty of the method were 2.7 %, 92.4-102.6 %, and 2.2 % (at 95 % confidence level (k = 2) assuming 1.0 mg/L thiosulfate in the sample solution), respectively.