激光烧蚀-电感耦合等离子体质谱法在食品接触金属材料镀层及其基材分析中的应用

采用激光烧蚀进样(LASI)与电感耦合等离子体质谱法(ICP-MS)测定相结合对与食品接触的金属材料的镀层及基材的快速分析。所用LSX-213型激光烧蚀进样系统具有单线扫描及深度分析两种模式。制作标准曲线及基材分析时采用单线扫描模式,对金属材料表面镀层分析采用深度分析模式。试验时,将载气氩气与氦气混合后引入LASI系统与LA释放出的样品混合形成气溶胶进入ICP-MS分析系统。每个试样在分析前先预烧蚀3次,之后重复烧蚀并采集数据7次,取其平均值。具体操作按仪器工作条件进行。用块状不锈钢标准样品制作了Si、Cr、Ni、Mn等4种元素的标准曲线,其线性范围依次为0.04%~2.0%,3.0%~20%,0.2%~20%和0.5%~20%,检出限(3S/N)依次为400,10.0,1.00,20.0ng·g^-1。对3件未知样品按此方法进行7次测定,测得Cr、Ni、Mn、Si等4种元素的平均相对标准偏差(n=7)依次3.2%,5.3%,3.9%,6.2%。应用所提出的方法分析了一件牛排刀样品和一件汤匙样品。在牛排刀的分析中,查明了此刀的刀身和刀柄属于两种不同规格的不锈钢,在制造中用了“灌铅技术”将两种钢材粘合在一起,造成了此食具中铅含量严重超标。在汤匙的分析中,确认其为镀金的不锈钢所制成。

Application of LA-ICP-MS to Analysis of Coatings and Its Metallic Matrixes of Food-Contacting Metallic Materials

By combining the laser ablation sample introduction (LASI) system with ICP-MS, a rapid method for analysis of coatings on metallic materials and also of their metallic matrixes was proposed. Two modes of laser ablation (LA), i.e. single-line scanning (mode A) and depth analysis (mode B), could be selected in the LSX-213 LASI system. Mode A was used in preparation of standard curves and in analysis of metallic matrixes, while mode B was applied to analysis of coatings on the surface of the metallic matrixes. In course of LA, mixed gas of Ar and He as the carrying gas was preintroduced into the LASI system, to mix with the ablated sample to form gaseous sol and carried over to the MS system for analysis. Before starting the analytical procedure, the sample should be preablated for 3 times, and then the analysis was started by repeated LA for 7 times, and the data were collcted and its average was taken. The analysis was performed as described in the instrumental working conditions. Standard curves for Si, Cr, Ni and Mn were prepared by the proposed method using standard sample of stainless steels in form of cakes, giving linearity ranges between 0.04% and 2.0%, 3.0% and 20%, 0.2% and 20%, 0.5% and 20% respectively. Detection limits (3S/N) found were 400, 10.0, 1.00, 20.0 ng·g^-1 respectively. 3 unknown samples were analyzed by this method, giving average RSDs (n = 7) of 3.2%, 5.3%, 3.9%, 6.2% for Cr, Ni, Mn and Si respectively. The proposed method was used to analyze 2 samples of food-contacting metallic materials, i.e., a steak knife and a soup spoon. In the analysis of steak knife, it was found that stainless steels of 2 different specifications were used in making the knife body and handle, and these 2 steels were bound together by a technology in which lead was used as adhesive, thus leading to the exceeding of content of lead beyond the limited value. In the analysis of a soup spoon, it was found that the spoon is made of stainless steel coated with gold.