Analysis of selenium in bovine liver by a gas chromatography with mass-selective, electron-capture and nitrogen-phosphorus detection

The concentration of selenium (Se) in liver was determined by gas chromatography (GC) with mass-selective (GC-MS), electron capture (GC-ECD) and nitrogen-phosphorus (GC-NPD) detection. Liver samples were digested in a mixture containing HNO₃ and Mg(NO₃). Se(VI) was converted to Se(IV). Se(IV) was derivatized with 4-nitrophenylenediamine and then extracted in toluene. A 1-μl volume of the toluene extract was analyzed by the GC-MS, GC-ECD or GC-NPD methods. The detection limits of the GC-ECD, the GC-NPD and the GC-MS methods were 25, 50 and 800 pg, respectively. The GC-NPD method was more selective for the derivatized Se than the GC-ECD method. The GC-MS method had the advantage of using the ⁷⁰Se isotope as the internal standard. Se concentrations in liver samples determined by the three methods were comparable.