Determination Of Some Heavy Metals In Soil By Laser Induced Breakdown Spectroscopy

Along with the rapid development of economy, the environmental contamination becomes a more and more serious issue, especially for heavy metal elements in soil. So the in-situ and real-time monitoring of heavy metals in soil is particularly important and necessary. Laser-induced breakdown spectroscopy (LIBS) is a promising technique for in situ environmental analysis with high precision, high sensitivity and few sample damage, and performs multi-element analysis with very little or no sample preparation. In recent years, growing concerns have focused on the real-time and in-situ monitoring of heavy metals in soil by LIBS.In this article, a brief introduction of the basic character and mechanism of laser induced plasma was presented. The basic principle for quantitative analysis by LIBS technique was introduced either. An experimental analytical system is set up, and optimized by varying the experimental condition. The behavior of shot to shot spectra line intensity variation emitted by the laser plasma was studied extensively. Based on this, a new data acquisition and processing procedure, sampling at a fixed position with optimum number of single-shot spectrum to be averaged, is used, which significantly improved the reproducibility and precision of measurement. The influence of laser energy and delay-time on the element line intensity, background radiation and noise in LIBS spectrum was investigated in detail. It was found that with specific laser energy, the signal-to-noise ratio (SNR) is first increase then decrease with the time delay, and exists an optimum delay time; while at a fixed delay time, the SNR is first increase then decrease with the increment of the laser energy. There is also an optimum laser energy. Furthermore, with the increment of laser energy, the optimum delay-time for best SNR will increase, and this phenomenon was qualitatively interpreted. Finally, we present the spectrum of the several soil samples under the optimized condition. According to the principle of inter-calibrate and outer-calibrate, the relations of signal intensity and element concentration of Ba, Ca, Cr, Sr and Pb in certified Reference soils were plotted and served as the calibration curves for elements analysis using LIBS technique . Good sensitivities were obtained,In addition, according to Boltzmann plot, the plasma temperatures of laser induced plasma of soil were derived. By comparing the laser plasma temperatures of different soil samples under identical experimental condition, the cause of the temperature difference was simply interpreted.