Combination of support vector regression (SVR) and microwave plasma atomic emission spectrometry (MWP-AES) for quantitative elemental analysis in solid samples using the continuous direct solid sampling (CDSS) technique

Abstract

Sample introduction has always been a significant issue in the research of plasma emission spectrometry. In this paper, the continuous direct solid sampling (CDSS) technique, a novel and alternative technique for direct solid analysis based on microwave plasma atomic emission spectrometry (MWP-AES), was firstly proposed. By allowing the plasma column to directly interact with the solid sample surface, the sample was heated and melted, and the elements in the sample were atomized and excited continuously. With the help of multivariate analysis, elements including C_org, Cu, Pb and Cr in geological samples were qualitatively and quantitatively determined. To construct a robust and accurate support vector regression (SVR) model, spectral bands consisting of characteristic lines and adjacent noise zones were selected as input variables. The penalty parameter C and the key parameter of the radial basis function (RBF) were optimized to be 16.0453 and 2.9008, respectively. The optimized model showed satisfactory results with a linearity correlation coefficient R² better than 0.99 and RSD lower than 11.08% for all target elements. The proposed CDSS technique can be used to successfully conduct direct solid analysis, avoiding the use of chemical reagents, which makes it green and environmentally friendly. The total analysis time can cost less than half a minute, indicating that the proposed method can be promising in high throughput and rapid analysis. What is more, the CDSS technique combines sampling, atomization and excitation together, which eliminates the use of an electrothermal vaporization or laser ablation unit when analyzing solid samples directly using MWP-AES. The proposed method opens a promising and alternative door for plasma spectrometry especially for MWP-AES due to the advantages of continuous direct solid analysis, rapid analysis speed, no or minimal sample pretreatment, and a simplified analytical system, which is suitable for in situ and field analysis.