Vapour phase Fourier transform infrared spectrometric determination of L-cysteine and L-cystine

A novel and selective procedure for the determination of L-cysteine and L-cystine based on vapour-generation Fourier transform infrared spectrometry is described. Potassium iodate solution was injected into a glass vessel containing L-cysteine and/or L-cystine. The evolved CO was swept by a stream of nitrogen to an infrared gas cell. The vapour phase FTIR spectra were continuously recorded, as a function of time, between 2240 and 2000 cm(-1), which includes the CO absorption band. The maximum absorbance at 2170 cm(-1) was selected as a measurement criterion. The calibration curve was linear over the range 6-300 mg L(-1) . The method provided a limit of detection of 2 mg L(-1) of L-cysteine, a throughput of 12 samples h(-1) and an R.S.D. of 1.76% for five independent analyses of a 75 mg L(-1) L-cysteine solution. For the measurement of L-cysteine and L-cystine separately, after measuring total concentration Of L-cysteine and L-cystine, L-cysteine was masked with p-benzoquinone at a pH of 3 and individual L-cystine was determined. The amount Of L-Cysteine was obtained by difference. The method was applied to the determination of L-cysteine and L-cystine in pharmaceutical and urine samples. Results obtained for real samples compared well with those obtained by a reference spectrometric method. (c) 2007 Elsevier B.V. All rights reserved.