Accuracy Improvement For Minor Elements Determination Using Modified Self-Absorption Correction And One-Point Calibration Laser-Induced Breakdown Spectroscopy

Abstract

Determination of minor elements is the weakness of one-point calibration laser-induced breakdown spectroscopy (OPC-LIBS), which greatly hinders the further development of OPC-LIBS. The normalization in minor elements determination is seriously influenced by self-absorption effect of matrix element in laser-induced plasma. In this work, a modified self-absorption correction method was proposed in OPC-LIBS. The plasma temperature was determined by the slope of Saha-Boltzmann plots established for minor elements, and the electron number density was calculated from the Hα line. The internal reference line of the matrix element was corrected and iterated, until the maximum value of the self-absorption coefficient in the analytical line of minor elements was less than 1. The correction factors were determined based on elemental concentration in the reference sample and Boltzmann plots, and then were used in other samples for elemental determination. Twelve certified 6061 reference aluminum alloy samples and seven micro-alloy steel samples were used as examples for demonstration. Compared with both conventional OPC-LIBS and IRSAC & OPC, the dist in the proposed method (modified IRSAC & OPC) was reduced to 0.537-1.632 wt.% and 0.891-2.805 wt. % for the aluminum alloy and micro-alloy steel, respectively. These results showed that the proposed method can improve the accuracy of detecting minor elements using only one reference sample, which greatly facilitates the application of LIBS.