Determination of selenium and tellurium compounds in biological samples by ion chromatography dynamic reaction cell inductively coupled plasma mass spectrometry

An ion chromatography–inductively coupled plasma mass spectrometric (IC–ICP–MS) method for the speciation of selenium and tellurium compounds namely selenite [Se(IV)], selenate [Se(VI)], Se-methylselenocysteine (MeSeCys), selenomethione (SeMet), tellurite [Te(IV)] and tellurate [Te(VI)] is described. Chromatographic separation is performed in gradient elution mode using 0.5 mmol L−1 ammonium citrate in 2% methanol (pH 3.7) and 20 mmol L−1 ammonium citrate in 2% methanol (pH 8.0). The analyses are carried out using dynamic reaction cell (DRC) ICP–MS. The DRC conditions have also been optimized to obtain interference free measurements of 78Se+ and 80Se+ which are otherwise interfered by 38Ar40Ar+ and 40Ar40Ar+, respectively. The detection limits of the procedure are in the range 0.01–0.03 ng Se mL−1 and 0.01–0.08 ng Te mL−1, respectively. The accuracy of the method has been verified by comparing the sum of the concentrations of individual species obtained by the present procedure with the total concentration of the elements in two NIST SRMs Whole Milk Powder RM 8435 and Rice Flour SRM 1568a. The selenium and tellurium species are extracted from milk powder and rice flour samples by using Protease XIV at 70 °C on a water bath for 30 min.