Heavy metals that can be absorbed by crops are usually called available heavy metals, which generally represent the pollution level of soil. Therefore, it will be very challengeable and interesting to detect the available heavy metal. Laser-induced breakdown spectroscopy (LIBS) is a spectrochemical analysis method based on analyzing spectra of plasmas that generated by pulsed lasers. With its merits of in situ, fast, and real time, it can be used for soil analysis. However, current LIBS always detects the total heavy metals in soil, whilst the available heavy metals detections are rarely reported.
To study how to detect available heavy metals in soil, Prof. Li Xiangyou and Dr. Yi Rongxing of advanced laser manufacturing group proposed a LIBS sample pretreatment method called phase transformation, in which HCl was used as an extractant to extract available heavy metals from soil to solution, and the solution was evaporated on a glass slide, then by analyzing the solid on the glass slide, the available heavy metals in soil can be easily and sensitively detected by this method (See figure below). Cd and Pb elements (more than 8% soil in China has been polluted by Cd and Pb elements) were used as two examples to test the proposed method, and the LODs of Cd and Pb elements in soil can reach to 0.067 and 0.98 ppm under optimized conditions, respectively. They are sufficiently low to meet the pollution limitation standards. For Cd element, the LOD meets the environmental quality standards for soils in China (0.2 ppm) for the first time by LIBS. For Pb element, the LOD is much lower than the soil pollution limitation standards in China (35 ppm).
The schematic of phase transformation method and the results
On May 12th, 2018，the paper “Determination of trace available heavy metals in soil using laser-induced breakdown spectroscopy assisted with phase transformation method” was published in Analytical Chemistry of the American Chemical Society（Anal. Chem., 2018, 90 (11), pp 7080–7085）. This research was financially supported by the Major Scientific Instruments and Equipment Development Special Funds of China (No. 2011YQ160017), the National Natural Science Foundation of China (No. 51429501, and 61575073)
