A colorimetric method for determining low concentrations of mercaptans

1. A method for the determination of mercaptans is described. It depends on the interchange of bis(p-nitrophenyl)disulfide and mercaptan anions at pH 8.0. 2. A study of the specificity of the reaction indicates that it occurs only with the S− group (actual or potential, as in thiourea). 3. Heavy-metal ions interfere with the reaction by irreversibly bonding any S− ions. 4. The kinetics of the reaction with cysteine and β-mercaptoethylamine were studied. 5. Several applications of this reaction were made: (a) the determination of mercaptan in synthetic compounds; (b) mercaptan reactivity in proteins; and (c) determination of blood and serum concentrations.