Capillary Electrophoresis Determination of Tiopronin in Human Urine After Derivatization with 2-chloro-1-methylquinolinium Tetrafluoroborate

An accurate, simple and sensitive method for determination of tiopronin (TP, N-(2-mercaptopropionyl)- glycine, Thiola) in human urine has been devised. Tiopronin is an important compound and is mainly used as a drug to prevent kidney stones. It works by removing the extra cystine from the body. Therefore, the reliable assay of tiopronin in biological matrices and pharmaceutical preparations is highly desirable. The proposed analytical procedure consists of reduction of tiopronin dimmer and its unsymmetrical disulfides with endogenous thiols, derivatization with 2-chloro-1- methylquinolinium tetrafluoroborate (CMQT) followed by acetonitrile stacking in capillary electrophoresis separation and ultraviolet-absorbance detection of TP-CMQT derivative at 350 nm. Baseline electrophoretic separation was achieved using standard fused-silica capillary (effective length 47.5 cm, 50 µm i.d.) and 0.25 mol L-1, Tris/HCl buffer adjusted to pH 2.0. The lower limit of quantitation for derivatized TP in urine was 5 µmol/L. The calibration curve showed linearity in the range 5-160 µmol L-1 urine with a regression coefficient corresponding to 0.9987 and the relative standard deviation of the points of the calibration curve being lower than 7%. The method can be used for a pharmacokinetic study with human subjects.