有机化合物对电感耦合等离子体质谱(ICP-MS)法测定食品中总砷的影响

Influence of Organic Compounds on Total Arsenic Determination in Food by Inductively Coupled Plasma Mass Spectrometry

为研究有机化合物对电感耦合等离子体质谱(ICP-MS)法测定食品中总砷的影响,分析总结一般规律,为食品中总砷的准确测定提供理论依据。通过考察甲醇和乙醇等14种有机化合物对ICP-MS法测定砷的动能歧视模式(KED)信号值和动态反应模式(DRC)信号值的影响,分析各有机化合物的电离能、极性和溶解度等性质,推测其在ICP-MS法测定体系中对砷响应信号值增敏或者抑制的可能机理。结果表明,有机化合物对ICP-MS的KED模式测定砷离子As^(+)的信号值有增敏效应,对DRC模式测定氧化砷离子AsO^(+)信号值的影响小于KED模式测定As^(+)的信号值,而且过程也更为复杂。相反,氮氧化物会减弱As^(+)和AsO^(+)的信号值。锗、铟等内标元素原子与砷原子在等离子体中电离行为和灵敏度的差异,使得内标元素校准砷测定信号的漂移受到干扰。推测有机化合物影响ICP-MS测定砷响应信号值的可能机理是:有机化合物和氮氧化物经电离或裂解之后分别生成碳离子或多原子碳离子和氮氧离子或氮氧基团,碳离子或多原子碳离子会与砷原子发生电荷转移反应,增强As^(+)或AsO^(+)的信号值,同时有机化合物也可能会与As^(+)竞争氧气而降低AsO^(+)的信号值,而具有强电负性的氮氧基团可能会与As^(+)和AsO^(+)发生电荷转移反应而减弱其信号值。有机化合物对砷的ICP-MS响应信号值的影响可能是受到有机化合物电离能、溶解度、极性和分子结构等综合因素的结果。

To study the influence of organic compounds on the determination of total arsenic in foods by inductively coupled plasma mass spectrometry(ICP-MS),analyze and summarize the general rules,and provide theoretical basis for the accurate determination of total arsenic in foods,the effects of 14 organic compounds,such as methanol and ethanol,on the kinetic energy discrimination mode(KED)signal value and dynamic reaction mode(DRC)signal value of ICP-MS in the determination of arsenic were studied,the ionization energy,polarity,solubility and other properties of the organic compounds were analyzed,and the possible mechanisms of their enhancement or inhibition of arsenic response signal value in the ICP-MS determination system was inferred.The results indicated that organic compounds had a sensitizing effect on the signal values of As^(+)determined by ICP-MS in KED mode,the effect on the signal values of AsO^(+)determined by DRC mode was smaller than that of As^(+)determined by KED mode,and with a more complex process.On the contrary,nitrogen oxides weakened the signal values of As^(+)and AsO^(+).The difference in ionization behavior and sensitivity between internal standard element atoms such as germanium,indium and arsenic atoms in plasma which interfered the calibration of arsenic drifting signals by internal standard elements.The possible mechanism of organic compounds which affect the signal value of arsenic response measured by ICP-MS may be carbon ions,polyatomic carbon ions,nitrogen oxide ions or nitrogen oxide groups generated by ionizing or splitting of organic compounds and nitrogen oxides,respectively.The generated carbon ions or polyatomic carbon ions had a charge transfer reaction with arsenic atoms to enhance the signal value of As^(+)or AsO^(+),organic compounds may also compete with As^(+)for oxygen and reduce the AsO^(+)signal value at the same time.On the other hand,strong electronegative nitroxide groups may have a charge transfer reaction with As^(+)and AsO^(+)to weaken their signal values.The influence of organic compounds on the ICP-MS response signal value of arsenic may be the result of comprehensive factors such as ionization energy,solubility,polarity and molecular structure of organic compounds.