The matrix effect is a phenomenon that ablated mass, elemental distribution, and laser absorptivity change with the matrix of the samples, which ultimately results in a significantly different signal response at the same concentration level in two different samples. This phenomenon deteriorates the accuracy of LIBS. The matrix of soil is complex due to the matrix changes with its geographical distribution, which creates an unavoidable problem in the field of soil analysis. Therefore, it is meaningful to find a way to reduce the matrix effect and improve the accuracy in soil analysis.

Under the guidance of Prof. Xiaoyan Zeng, Yongfeng Lu, Xiangyou Li and associate professor Lianbo Guo, Rongxing Yi et al. proposed a method of discrete wavelet transform combined with standard addition method (SAM) for analyzing soil samples. The SAM was used to reduce the matrix effect, the algorithm of discrete wavelet transform was used to improve the analytical accuracy of trace elements in soil. The results demonstrated that the accuracies of quantitative analyses on lead (Pb) and cadmium (Cd) in soil were all improved by this method,especially for the low concentration samples.

This research has been financially supported by the National Special Fund for the Development of Major Research Equipments and Instruments (No. 2011YQ160017), the National Natural Science Foundation of China (No.61575073 and 51429501),  and Natural Science Foundation of Hubei province (No. 2015CFB298), which has been published on the journal of Optics Express (Vol. 24, Issue 3, pp. 2607-2618, 2016)

Figure 1. Experiment setup

Figure 2. Calibration line of Pb