Determination of cobalt compounds in dietary supplements using liquid chromatography inductively coupled plasma mass spectrometry

Speciation of Co in dietary supplements is reported by combining microwave-assisted extraction (MAE) with high-performance liquid chromatography (HPLC), inductively couple plasma mass spectrometry (ICP-MS), and a membrane desolvation sample introduction system. Reversed-phase HPLC with a microbore C8-column as the stationary phase and gradient elution (ammonium acetate/acetonitrile, pH 4) resulted in the separation, within 14 min, of the Co-containing species Co(II), cyanocobalamin (CN-Cbl), hydroxylcobalamin (OH-Cb1), and, most notably, the strongly adsorbing 5'-deoxyladenosylcobalamin (Ado-Cbl), and methylcobalamin (Me-Cbl). For a 5 mu L sample loop, the detection limits were in the range 0.007 to 0.031 ng Co mL(-1). We applied this approach on selected dietary supplements and a couple of functional drinks. Over 91% of the total Co species were extracted through MAE using a 0.5% (v/v) HNO3 solution; the spike recoveries were in the range 94 to 101%. The results obtained from HPLC-ICP-MS analysis of the functional drinks and dietary supplements were in agreement with the total Co concentrations measured through ICP-MS analysis.