应用便携式X射线荧光光谱仪对土壤中Cr,Cu,Zn,As,Pb等重金属含量进行检测,每个样品扫描检测3次,利用小波阈值滤噪的方法对所测谱线进行光滑去噪处理后,根据土壤重金属的标准值和相应的计数率(取三次处理后检测谱线的平均值)建立各重金属的标准曲线.运用小波阈值滤噪方法时,为确定最佳的小波基和小波分解层数,以信噪比(SNR),均方根误差(MSE)和信息熵(H)作为评估指标评价降噪效果.为验证仪器的稳定性,根据土壤样品中重金属浓度的不同挑选部分样品并同时选用H3BO3(空白对照)进行重测.结果表明:运用小波变换方法时,选取coif3小波基对谱线进行三层分解,取得了最佳的去噪效果;建立好模型后,仪器的决定系数R2范围是0.990~0.996,表明在0~1 500 mg·kg-1范围内,土壤样品中各重金属元素含量与X射线荧光光谱特征峰强度之间的线性关系良好;经过重复检测和计算得知仪器的检出限均低于国家一级土壤标准.将小波变换的方法实际运用到X射线荧光光谱仪检测模型的建立与改进中,有效的提高了模型的准确性,同时经验证,仪器具有良好的精密度,可运用于实际土壤重金属污染的现场快速筛查.

The concentration of Cr,Cu,Zn,As and Pb in soil was tested by portable X-ray fluorescence spectrometer.Each sample was tested for 3 times,then after using wavelet threshold noise filtering method for denoising and smoothing the spectra,a standard curve for each heavy metal was established according to the standard values of heavy metals in soil and the corresponding counts which was the average of the 3 processed spectra.The signal to noise ratio (SNR),mean square error (MSE) and information entropy (H) were taken to assess the effects of denoising when using wavelet threshold noise filtering method for determining the best wavelet basis and wavelet decomposition level.Some samples with different concentrations and H3BO3 (blank) were chosen to retest this instrument to verify its stability.The results show that:the best denoising result was obtained with the coif3 wavelet basis at the decomposition level of 3 when using the wavelet transform method.The determination coefficient (R2) range of the instrument is 0.990~0.996,indicating that a high degree of linearity was found between the contents of heavy metals in soil and each X-ray fluorescence spectral characteristic peak intensity with the instrument measurement within the range(0~1 500 mg·kg-1).After retesting and calculating,the results indicate that all the detection limits of the instrument are below the soil standards at national level.The accuracy of the model has been effectively improved,and the instrument also shows good precision with the practical application of wavelet transform to the establishment and improvement of X-ray fluorescence spectrometer detection model.Thus the instrument can be applied in on-site rapid screening of heavy metal in contaminated soil.