COBALT(II) AS A TITRANT IN THE DIRECT POTENTIOMETRIC TITRATION OF MICRO-AMOUNTS OF L-CYSTEINE

A method for the determination of micro-amounts of cysteine by potentiometric titration in aqueous buffered solution with 5 mmol dm-3 of cobalt(II) is described. The end-point of the titration is detected by using a sulfide ion-selective electrode and a double-junction reference electrode. In the automated titration of 0.5-4 mg of cysteine, results accurate to within +/-0.70% are obtained with appropriate standardization of the titrant; the results are reproducible to within +/-0.60% and the relative standard deviation in the titration of 1 mg of cysteine is 0.28%. The use of cobalt(II) as a titrant has proved to be a valuable alternative to previously described methods. Cystine and methionine do not interfere.