Development of two flow analysis methods for the determination of tiopronin in pharmaceuticals

A flow injection analysis (FIA) method and the first sequential injection analysis (SIA) method for the determination of tiopronin in pharmaceuticals have been developed. Both utilize the one-step colour reaction involving the reduction of the Cu(II)-bathocuproine complex by tiopronin to the orange-coloured Cu(I)-bathocuproine complex with maximum absorbance at 483 nm. The FIA and SIA methods exhibit linear calibration ranges of 4.0 × 10^-7 - 4.0 × 10^-5 and 4.0 × 10^-7 - 6.0 × 10^-5 mol L^-1, repeatability (expressed as relative standard deviation) of 1.4 and 2.9 % and sampling rates of 180 and 36 h^-1, respectively. Both methods are characterised by limits of detection and quantitation of 1.4 × 10^-7 and 4.6 × 10^-7 mol L^-1, respectively. They have been successfully applied to the determination of tiopronin in a pharmaceutical. No statistically significant difference has been observed between the two methods, and between each one of them and the standard Pharmacopoeia method on one hand and the amount of tiopronin per tablet quoted by the tablet manufacturer. Good recovery results for both flow methods have been also obtained with spiked tablet samples. Based on the sampling rate and reagent consumption results, it has been concluded that the FIA method, which offers a higher sampling rate than existing FIA methods, is more suitable for the analysis of large numbers of samples while the SIA method minimises analysis costs and the generation of chemical waste.