ICP-MS Detection for HPLC Analyses of Pharmaceutical Products

Experiments using inductively coupled plasma-mass spectrometry (ICP-MS) as a detection system for reversed-phase chromatographic methods have been conducted for the analyses of various pharmaceutical compounds. Interfacing the ICP-MS instrument to the high performance liquid chromatography (HPLC) system was straightforward. The eluent from the HPLC column was pumped through a photodiode array (PDA) and then directly into the ICP-MS nebulizer using standard sample introduction components at flow rates ranging from 0.5 to 1.5 mL/min. Two separate sets of experiments were carried out. Initial speciation experiments were conducted on the B supplements cyanocobalamin (vitamin 11312), biotin, and thiamine (vitamin B-1)using isocratic separations. ICP-MS chromatograms were generated by monitoring cobalt at m/z 59, phosphorus at m/z 31, and sulfur at m/z 34 simultaneously. Linear regression data were obtained for cyanocobalamin, thiamine hydrochloride, and biotin. Elemental detection was used to resolve coeluted thiamine and cyanocobalamin peaks in a rapid isocratic separation. The signal for biotin in the sulfur chromatogram was determined to be much larger than that of the corresponding UV chromatogram at 250 nm. In the second set of experiments, an active pharmaceutical ingredient (API) was hydrolyzed with base to monitor the parent compound and two degradation products: degradation product 1 (DP1) and degradation product 2 (DP2). The API molecule contains bromine, chlorine, and sulfur; DP1 contains bromine and sulfur; and DP2 contains chlorine. The ions monitored for analysis of API, DP1, and DP2 were m/z 79 for bromine, m/z 35 for chlorine, and m/z 34 for sulfur. The calculation of relative amounts of API, DP1, and DP2 from the bromine, chlorine, and sulfur chromatograms was performed. The data suggest that the same calculation performed from the UV chromatogram introduces a bias due to the difference in extinction coefficients for each compound. The capacity for monitoring UV absorbance and elemental ions sequentially was demonstrated to provide enhanced analytical specificity without requiring interpretation of complex mass spectra.