Flow-injection Spectrophotometric Determination of Tiopronin Based on Coupled Redox-Complexation Reaction

A flow-injection spectrophotometric procedure for determination of N-(2-mercaptopropionyl)-glycine (MPG) tropronin has been proposed. Determination was based on the coupled redox-complexation reaction between MPG, Fe(Ill) and 2,4,6-trypyridyl-S-triazine (TPTZ). Firstly, MPG reduced Fe(III) to Fe(II), which was rapidly converted to the highly stable, deep-blue coloured Fe(TPTZ)(2)(2+). This coloured complex was monitored at 593 nm. Optimal conditions for determination of MPG were obtained applying the univariate method. A linear calibration curve was established in MPG concentration range 6.0 x 10(-6)-2.0 x 10(-4) mol L-1 with regression equation y = 4675 x -0.0195 (R-2 = 0.9999) (n = 9) and detection limit of 4.0 x 10(-6). Analytical frequency was 60 h(-1). The proposed method was simple, rapid, sensitive and reproducible (RSD 0.5%, n = 10). It can be applied to determination of up to nanomolar levels of MPG in pharmaceutical preparations. Usual excipients used as additives in pharmaceuticals did not interfere with determination.