Decreasing the effect of soil particle size on heavy metal measurement stability using a method involving laser-induced breakdown spectroscopy and solid-phase conversion

Heavy metals in soil pose risks to human health and can cause poisoning or even death. It is therefore important to develop a method for quickly determining the heavy metal contents of soil. Laser-induced breakdown spectroscopy (LIBS) is a new technique for determining elements that has been used widely to analyze soil. LIBS allows rapid on-site soil analysis. However, matrix effects caused by different soil particle sizes prevent accurate measurements of elements in soil if the soil is not preprocessed. We developed a solid phase conversion (SC) and LIBS method to improve the stability of measurements of heavy metals in soil and compared the results with the results of direct measurement and tableting methods. The relative standard deviations for the Pb and Cr contents determined by SC-LIBS were 11% and 10%, respectively. The mean relative standard deviations for Pb and Cr were 71.4% and 53.4% lower, respectively, for SC-LIBS than for the direct measurement and tableting methods. The root mean square errors for SC-LIBS were 25.37 and 36.89 mg kg-1 for Pb and Cr, respectively. The average root mean square errors for Pb and Cr were 27.1% and 19.7% lower, respectively, for SC-LIBS than for the direct measurement and tableting methods. The limits of detection for Pb and Cr determined by SC-LIBS were 9.34 and 3.60 mg kg-1, respectively. The results indicated that SC-LIBS effectively decreases matrix effects and improves the accuracy and stability when determining heavy metals in soil. A solid-phase method for soil treatment combined with LIBS, which has high stability and good quantitative effect.