[Determination of trace elements in waste beer yeasts by ICP-MS with microwave digestion]

The waste beer yeast has rich nutritional compositions and is widely used in food, medical and forage industries. The security of the yeast plays an important role in everyone's daily life. But the yeast contanining microamount of lead, cadmium, chromium, arsenic and other harmful metals is endangering human health. A new method was developed for the direct determination of eight elements, namely copper, lead, zinc, iron, manganese, cadmium, chromium and arsenic in waste beer yeast by inductively coupled plasma-mass spectrometry (ICP-MS) with microwave digestion. The parameters of plasma system, mass system, vacuum system and spectrometer system were optimized. The spectral interferences were eliminated by selecting alternation analytical isotopes of 65Cu, 208Pb, 66Zn, 57Fe, 55Mn, 114Cd, 52Cr and 5As, and the internal standards of Rh was selected to compensate the drift of analytical signals. The samples were digested with concentrated nitric acid-hydrogen peroxide (2:1) mixed solution more rapidly and more effectively. The effects of the type of mixed acid , the volume of digesting solution, heating time, and heating power were investigated in detail. In the closed system, the complete digestion was performed using 4 mL HNO3 and 2mL H2O2 for 2.0 min at 0.5 MPa, 3 min at 1.0 MPa and 5 min at 1.5 MPa. The detection limits of these eight elements were 0.013-0.122 microg x L(-1). The relative standard deviation (RSD) was 0.94%-3.26% (n=9), and the addition standard recovery was 98.4%-102.6% for all elements. The proposed method has been applied to the determination of trace elements of Cu, Pb, Zn, Fe, Mn, Cd, Cr and As in waste beer yeast samples with satisfactory results. The determination results indicated that the content of trace elements of Cu, Pb, Cd and As in waste beer yeast samples are significantly low.