微波消解ICP-MS法测定啤酒废酵母中的微量金属元素

建立了微波消解-电感耦合等离子体质谱法(ICP-MS)同时测定啤酒废酵母粉中铜、铅、锌、铁、锰、镉、铬和砷等八种微量元素的方法。在实验中，对仪器的最佳工作参数进行了优化，选择适当的同位素，并用铑作内标元素，有效地抑制了分析信号的漂移及分子和多原子离子的质谱干扰；探讨了混合酸消解体系、消解液用量、微波消解功率及时间对测定结果的影响。以HNO₃-H₂O₂(2∶1)作为消化试剂，在0.5 MPa压力下2 min，1.0 MPa压力下3 min，1.5 MPa压力下5 min，4 mL HNO₃和2 mL H₂O₂能完全消解样品。在选定的实验条件下，对五种啤酒废酵母粉样品进行了精密度和回收率实验，方法相对标准偏差在0.94%～3.26%(n=9)之间，加标回收率在98.4%～102.6%之间。

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 75As, 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 μg·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.