Determination of thio-based additives for biopharmaceuticals by pulsed electrochemical detection following HPLC

Pulsed electrochemical detection (PED) following liquid chromatographic separation has been applied to the direct (i.e., without derivatization) determination of two major sulfur-containing compounds used as pharmaceutical additives, isopropyl-thio-β-d-galactopyranoside (IPTG) and monothioglycerol (MTG). Limits of detection of IPTG and MTG were found to be 1 ppb (0.2 pmol, 50 μL) and 0.2 ppb (0.1 pmol, 50 μL), respectively, using optimized potential-time waveforms applied to a Au electrode. In addition to high sensitivity as compared to optical detection, the simultaneous detection of free thiols and disulfides can be used to study the kinetics of these conversions, as is shown for MTG. A practical application of HPLC-PED is demonstrated in determining MTG in a pharmaceutical formulation. The high selectivity of PED for thiocompounds reduces sample preparation and produces simpler chromatograms in a variety of matrices.