单波长激发能量色散X射线荧光光谱测定土壤样品中镉等元素方法性能评估

用X射线荧光光谱仪(XRF)准确测定土壤样品中低含量Cd(～0.3 mg/kg)一直是个难题。实验利用4个系列129个土壤、沉积物标准样品和实际土壤样品,用基准比值法、相对误差(相对偏差)频率分布和相对误差(相对偏差)绝对值在不同含量范围的分布数据,系统评估了采用双曲面弯晶(HF-DCC)全聚焦技术实现的单波长激发能量色散X射线荧光光谱仪(SW-ED-XRF)和基本参数法测定土壤样品中低含量Cd等重金属元素的实际效果。结果表明,用SW-ED-XRF测定土壤样品中重金属元素As、V、Pb、Cr、Cu、Zn、Ni、Mn的方法检出限、精密度和准确度与常规波长色散X射线荧光光谱仪(WD-XRF)和能量色散X射线荧光光谱仪(ED-XRF)相当,准确度合格率大于90%,能够满足检测实验室质控要求。采用SW-ED-XRF定量分析土壤样品中Cd,测量时间分别为90 s和300 s时,检出限分别为0.2 mg/kg 和0.05 mg/kg。用重复测定法、背景计数法和校准曲线法相互验证了Cd检出限结果。用人眼可分辨的Cd谱峰对应的最低含量确认了Cd检出限的合理性。90 s条件下,Cd准确度合格率为79.6%,优于常规WD-XRF和ED-XRF。土壤样品中低含量Cd的XRF快速测定已有明显进步。

Performance evaluation of single wavelength excitation energy dispersive X-ray fluorescence spectrometry for determination of cadmium and other elements in soil samples

It is always a difficult task to accurately determine the low content cadmium (0.3 mg/kg) in soil samples by X-ray fluorescence spectrometer (XRF). The content of heavy metals such as cadmium in 129 standard samples of soil and sediment, and actual samples of soil from 4 series were determined by the single-wavelength excitation energy dispersive X-ray fluorescence spectrometer (SW-ED-XRF) based on hyperboloid curved crystal (HF-DCC) full focusing technique and basic parameter method. The actual performance was systematically evaluated using the reference ratio method, the relative error/relative deviation frequency distribution and the relative error/relative deviation (absolute value) distribution data in different content ranges. The results showed that the limit of detection, precision and accuracy of heavy metals such as As, V, Pb, Cr, Cu, Zn, Ni and Mn in soil samples determined by SW-ED-XRF were comparable to those obtained by conventional wavelength dispersive X-ray fluorescence spectrometer (WD-XRF) and energy dispersive X-ray fluorescence spectrometer (ED-XRF). The pass rate of accuracy was greater than 90%, which could meet the quality control requirements of testing laboratories. The content of cadmium in soil sample was quantitatively analyzed by SW-ED-XRF. When the measuring time was 90 s and 300 s, the limit of detection was 0.2 and 0.05 mg/kg, respectively. The results of limit of detection of cadmium were mutually verified by repeated determination method, background counting method and calibration curve method. The rationality of limit of detection of cadmium was confirmed by the lowest content corresponding to its spectral peak which could be distinguished by human eyes. When the measuring time was 90 s, the accuracy qualification rate of cadmium was 79.6%, which was better than that of conventional WD-XRF and ED-XRF. The rapid determination of low-content cadmium in soil samples had made significant progress.