Multi-element determination in soil using laser-induced breakdown spectroscopy with only one internal reference element by one-point calibration

Abstract

Soil elemental analysis is vital for assessing nutrient availability and contamination. For soil analysis, conventional calibration-free LIBS (CF-LIBS) methods suffer from unavoidable uncertainty of the Einstein coefficients and optical coefficients. Although one-point calibration LIBS (OPC-LIBS) can tackle these problems to some degree, it is still limited by the self-absorption effect and strict requirement of accuracy of all-elemental content. In this work, a modified OPC-LIBS method was proposed, which combines an internal reference element strategy with self-absorption correction and columnar-density Saha–Boltzmann (CD-SB) plotting. Only one major element, silicon, needed to be certified in the reference soil sample. All other elements across diverse soils were deduced. Moreover, self-absorption and plasma parameters (temperature and electron density) were corrected via CD-SB plots, providing a more reliable basis for elemental determination. The results demonstrated that mean relative errors (MRE) were reduced to 16.324–42.358% in the proposed method, much lower than in conventional CF-LIBS and in CF-LIBS with self-absorption correction. The analytical accuracy also matched or outperformed conventional OPC-LIBS (requiring certification of all elements in the reference sample). This work provided a more convenient and accurate method for multi-element soil analysis.