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 pre-ablated 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.