Combined use of HPLC–ICP-MS and microwave-assisted extraction for the determination of cobalt compounds in nutritive supplements

Speciation analysis of cobalt in nutritive supplements has been carried out using HPLC and ICP-MS equipped with a membrane desolvation sample introduction system as detector. In this study, cobalt containing compounds, namely Co(II), cyanocobalamin (CN-Cbl) and hydroxylcobalamin (OH-Cbl), were well separated by reversed phase HPLC with a C8-HPLC column as the stationary phase and 8 mmol L−1 ammonium acetate in 22% v/v methanol solution (pH 4) as the mobile phase using isocratic elution. Detection limit was in the range of 0.008–0.014 μg Co L−1 for various Co species. Over 98% of the total cobalt species was extracted in nutritive supplements using a 0.5% v/v HNO3 solution in a microwave field; and the spike recovery was in the range of 92–108% for various species. The HPLC–ICP-MS results showed a satisfactory agreement with the total cobalt concentrations obtained by ICP-MS analysis of completely dissolved samples.