The effect of self-absorption compensation methods on the quantitative analysis of soil samples using Laser-induced breakdown spectroscopy

Abstract

When the detection of heavy metal elements in the soil was conducted using Laser-induced breakdown spectroscopy (LIBS), the accuracy of the calibration model can be affected by the self-absorption effect. In this work, the piecewise fitting and the least square support vector machine (LSSVM) were used to reduce the influence of self-absorption effect on quantitative analysis of the Cr element in the soil. With the increase of the Cr element content, the increased rate of the Cr element emission intensity decreases using internal standard method under the best conditions. The non-linear relationship exists between the content of the Cr element and the emission intensity of the Cr element, which reduces the accuracy of the quantitative analysis. Hence, the self-absorption coefficient (SA) was evaluated. The results showed that the self-absorption effect becomes more and more serious with the increase of element content. Therefore, the piecewise fitting and the LSSVM algorithm were used to establish calibration model. The correlation coefficients of the calibration model based on piecewise fitting were 0.9918, 0.9787 and 0.9655, respectively. The root mean square error (RMSE) and mean relative error (MRE) of the calibration model of piecewise fitting were 1.2853 wt% and 15.64%, respectively. Compared with the piecewise fitting calibration model, the LSSVM calibration model performed best, with an overall correlation coefficient of 0.9902, RMSE and MRE of 0.3878 wt% and 8.9926%, respectively. The results indicated that the LSSVM algorithm can be used as a method of reducing the influence of the self-absorption effect on the calibration model.