Contributions to the chemistry of human hair. 1. Analyses of cystine, cysteine and cystine oxides in untreated human hair.

Synopsis Amino acid analysis, photometry and polarography were selected as analytical methods for the determination of thiol and disulphide groups in untreated human hair and the results are discussed. The pre-treatments necessary for the different analytical methods, e.g., hydrolysis, to some extent already induce chemical changes of the cysteine and cystine derivatives leading to method-dependent differences in the results. In many cases the partial oxidation products of cystine are supposed to be responsible for this effect. Electron Spectroscopy for Chemical Analysis (ESCA), as an analytical method for the determination of the cystine oxides, was found to be inapplicable due to insufficient resolution and sensitivity, whereas by the use of Fourier Transform Infrared (FTIR) Spectroscopy the sulphur-oxygen vibrations could be analysed and cystine monoxide and cystine dioxide were detected.