Laser-induced breakdown spectroscopy; Quantitative analysis; Standard addition method; Curve fitting; Heavy metals;
Quantitative analysis of four heavy metals Pb, Cr, Cu and Cd in soils and solid wastes using independently developed portable system of laser-inducedbreakdown spectroscopy. A Nd: YAG pulse laser with fundamental wavelength of 1 064 nm is used as the excitation source, with the single pulse energy of 100 mJ the pulse width of 6 ns, and the operating frequency 3 Hz. The echelle spectroscopy with high resolution and wide spectral range is used as the spectral separation device, and the intensified charge coupled device GOOD) as the spectral detection device in the experiment, with the detection range of 200 similar to 500 nm and a resolution of 0.08 similar to 0.12 nm. In order to improve the spectral intensity and detection sensitivity, a device of hemisphere spatially bound is used to restrain the plasma and a optical fiber with multi-channel is used collect the signal. The reception angle is 45 degrees. The laserrepetition rate is 2 Hz while the delay is 1.5 mu s, with the gate width of 1.05 ms. Standard addition method is used to effectively solve the quantitative analysis of samples of unknown matrix. The innovation lies in the fact that, a curve fit instead of a straight line fit is used in the standard addition method to quantitative analyze the heavy metals in soils and solid wastes, which effectively improve the measurement results. Especially for the low concentrations of soil samples, linear fitting can not be used in quantitative analysis, in contrast, the correlation coefficient of curve fitting is much higher, more closer to the national standard measurement methods, to meet soil pollution detection. The result of seven soils and solid wastes samples are as follows, line fitting relative error: Pb 1.26%similar to 79.38%, Cr-22. 44%similar to 82.06%, Cu 15.09%similar to 190.50%, Cd 32.76%similar to 167.96%, and curve fitting relative error respectively Pb - 4.19%similar to 11.92%, Cr-38.31%similar to 9.26%, Cu-7.24% similar to 26.86%, Cd-10.52%similar to 12.94%, the average relative error is 10.47%.