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A simple flow injection spectrophotometric method is reported for the determination of cysteine,N-acetyl cysteine and glutathione based on the reduction of Fe(Ⅲ)/ferricyanide,the in situ reduced ions are reacted with unreduced portion of ferricyanide/Fe(Ⅲ) to form soluble Prussian blue,which is monitored at 735 nm.The calibration graphs are linear in the concentration ranges of(1―100)×10-6 mol/L for cysteine and N-acetyl cysteine,and(1―50)×10-6 mol/L for glutathione.The relative standard deviations of 1.8%,2.5% and 1.9% were found for eleven replicate analyses of 5×10-6 mol/L cysteine,N-acetyl cysteine and glutathione.The limits of detection(3σ blank) at 5×10-7 mol/L for cysteine,and 3×10-7 mol/L for N-acetyl cysteine and glutathione were obtained.The proposed method allowed 60 injections/h.The effects of common substances present in pharmaceuticals and human physiological fluids were examined.The method was applied to determining cysteine in pharmaceutical formulations with the recoveries in a range of 97% to 106% and the results obtained are agreed well with labeled values.
A simple flow injection spectrophotometric method is reported for the determination of cysteine, N-acetyl cysteine and glutathione based on the reduction of Fe (III) / ferricyanide, the in situ reduced ions are formed with unreduced portion of ferricyanide / Fe (III) to form soluble Prussian blue, which is monitored at 735 nm. The calibration graphs are linear in the concentration ranges of (1-100) × 10 -6 mol / L for cysteine and N-acetyl cysteine, and (1-50) × 10 -6 mol / L for glutathione. The relative standard deviations of 1.8%, 2.5% and 1.9% were found for eleven replicate analyzes of 5 x 10-6 mol / L cysteine, N-acetyl cysteine and glutathione. The limits of detection ( 3σ blank) at 5 × 10-7 mol / L for cysteine, and 3 × 10-7 mol / L for N-acetyl cysteine and glutathione were used. The proposed method allowed 60 injections / h. The effects of common substances present in pharmaceuticals and human physiological fluids were examined.The method was applied to determining cysteine in pharmaceutical formulations w ith the recoveries in a range of 97% to 106% and the results obtained are agreed well with labeled values.