Voltammetric determination of volatile free sulfide and alkylthiols as contaminants in parenteral amino acid solutions

A method for the simultaneous voltammetric determination of free sulfide an d volatile alkythiols (methanethiol/ ethanethiol) existing as contaminant i n parenteral nutrition (PN) solutions was developed. The volatile sulfides (dihydrogensulfide and alkylthiols) formed in the formulations were distill ed over 45 min at 47 degreesC in a purpose-made Conway cell. The analytes w ere quantified by differential pulse cathodic stripping voltametry (DPCSV) at the hanging mercury-drop electrode and determined, simultaneously as dih ydrogensulfide and alkylthiols using a 60 s preconcentration time at - 300 mV (versus Ag/AgCl, Cl- 3.0 mol 1(-1)). The voltammetric signals were direc tly linear proportional to the sulfides concentrations in the PN solutions in the range 3-20 mu mol 1(-1) and detection limits of about 2 mu mol 1(-1) were calculated. Recoveries of sulfides from PN solutions in the range 90- 110% were calculated using the method and nine commercial PN formulations w ere analyzed. Methanethiol and ethanethiol were quantified from their compo site signals, and the mutual influence of the analytes on the DPCSV measure ments is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.