电感耦合等离子体质谱法测定饲料中14种主量和痕量元素的含量

取饲料样品0.200 0～0.500 0g,加入硝酸5mL,按程序升温模式进行消解。所得消解液于100℃蒸缩至其体积约为1mL,用水将样品溶液定容至50.0mL。采用电感耦合等离子体质谱法测定溶液中9种主量有益元素(K、Na、Ca、P、Mg、Fe、Cu、Zn、Mn)和5种痕量有害元素(Cr、Pb、As、Cd、Hg)。在质谱测定中,为避免同量异位素的干扰,选择被测元素相对丰度较高的同位素作为测定元素,例如为了避免40 Ar的干扰,选择44 Ca作为待测元素;又如测54 Fe时受到54 Cr的干扰,为避免此干扰,选择56Fe作为待测元素;另一类质谱干扰为多原子离子(如ArCl及N和O生成的多原子离子)的干扰。但上述9种主量元素的浓度远高于干扰测定的多原子离子的浓度,因此,其干扰可以忽略。对5种痕量元素的测定而言,由于生成多原子离子所引起的干扰,可用数学干扰校正方程消除其影响。此外测定汞时,可加入金形成金汞齐,以消除汞的吸附效应。在测定中选择钪、镍等8种元素分别作为相关测定元素的内标元素,以校正信号漂移和基体效应。试验结果表明:14种元素的质量浓度在一定范围内与其信号强度呈线性关系,测定下限(10s/k)在1.65×10-4～6.60mg·kg^-1范围内。按标准加入法进行回收试验,测得其回收率在83.0%～115%之间,测定值的相对标准偏差(n=7)在0.4%～12%之间。

Determination of 14 Main and Trace Elements in Feeds by ICP-MS

The feed sample(0.200 0 g to 0.500 0 g)was digested with 5 mL of HNO3 under the mode of programmed temperature elevation.The digested solution was then concentrated to ca.1 mL by heating at 100 ℃.The solution was then cooled and diluted to 50.0 mL with water,and 9 major and beneficial elements,i.e.,K,Na,Ca,P,Mg,Fe,Cu,Zn and Mn,and 5 harmful trace elements,i.e.,Cr,Pb,As,Cd and Hg,were determined in this sample solution by ICP-MS.MS interferences by isobaric elements were avoided by selecting the isotope with higher relative abundance as the analytical species for the analyte.For instance,44Ca was selected instead of 40Ca as the determining species to avoid the interference of 40Ar;56Fe was used instead of 54Fe to avoid the interference of 54Cr,and etc.Another kind of MS interference was the formation of poly-atomic ions,e.g.ArCl and poly-atomic ions formed between N and O.But concentrations of the 9 major elements were significantly higher than that of the polyatomic ions possibly formed,hence their interferences were neglected.While in the determination of the 5 trace elements,such interferences could be avoided by applying mathematical equation of interference correction.Besides,in the determination of Hg,Au was added to form Hg-Au amalgam in order to avoid the adsorption effect of mercury.Furthermore,for control and correction of signal drifts and matrix effects in the determination of the 14 elements,8 elements,including Sc,Ni and etc.,were added as internal standards separately in the relative determination.As shown by the testing results,linear relationships were found between values of the singal strength and mass concentration of 14 elements in definite ranges,and their lower limits of determination(10 s/k)ranged from 1.65×10^-4 to 6.60 mg·kg^-1.Tests for recovery were made by standard addition method,giving values of recovery in the range of 83.0%-115%,and values of RSDs(n=7)ranged from 0.4% to 12%.