Effect and Correction of Iron in Soil on Accuracy of Chromium Determination by Portable X-ray Fluorescence Spectrometry
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摘要: 便携式X射线荧光光谱仪(p-XRF)能够快速检测土壤中的铬元素,但由于土壤成分复杂、基体效应不明,导致其检测准确度较低。铁元素作为土壤基体中的主量元素,在不同类型土壤中含量变化范围大,是影响铬元素p-XRF测定准确度的主要元素之一,深入研究铁元素对铬元素荧光强度的影响有助于提高p-XRF测定土壤中铬元素的准确度。本文以人工配置的铬-铁土壤样品研究铬元素荧光强度与铬元素含量和铁元素含量的变化关系,采用经验公式校正铁元素对铬元素p-XRF分析准确度的影响。结果表明:土壤样品中的铁元素含量固定不变时,铬元素的含量与其相应的特征X射线荧光强度呈线性变化,相关系数均在0.9990以上,且铬元素荧光强度的增长速率随着土壤中铁元素含量的增加而增大;另外通过对同一铬含量、不同铁含量土壤样品的研究,验证了铁元素对铬元素的荧光增强效应,并发现该增强效应还与铁、铬元素的相互作用有关。结合铬、铁元素基体效应研究结果,本文建立了铁元素对铬元素p-XRF测定的校正方程式,相比于普通的线性回归,该方法的相关系数从0.9011提高到了0.9986,硅藻土样品的p-XRF分析平均相对误差从21.94%下降至2.52%,实际土壤样品的p-XRF分析平均相对误差从51.02%下降至5.21%。Abstract:
BACKGROUNDThe portable X-ray fluorescence spectrometer (p-XRF) can detect chromium in soil rapidly, but its detection accuracy is low because of the complexity of soil composition and the unknown matrix effect. As the main element in soil matrix, iron content varies widely in different types of soil, which is one of the main elements affecting the accuracy of p-XRF determination of chromium. OBJECTIVESTo improve the accuracy of p-XRF in the determination of chromium in soil. METHODSThe relationship between the fluorescence intensity of chromium and the content of chromium and iron was studied by using artificial soil samples with added chromium and iron. A calibration model was established based on research results. RESULTSWhen the content of iron in the soil sample was fixed, the content of chromium changed linearly with its corresponding characteristic X-ray fluorescence intensity, and the correlation coefficients were all above 0.9990. Moreover, the growth rate of the fluorescence intensity of chromium increased with the increase of iron content in the soil. In addition, through the study of soil samples with the same chromium content and different iron content, the fluorescence enhancement effect of iron on chromium was verified, and it was found that the enhancement effect was also related to the interaction of iron and chromium. CONCLUSIONSCombining the research results of matrix effects of chromium and iron, the correction equation of effect of iron on p-XRF determination of chromium has been established. Compared with ordinary linear regression, the correlation coefficient of this method increased from 0.9011 to 0.9986. The average relative error for p-XRF analysis of diatomite samples decreased from 21.94% to 2.52%, and the average relative error of p-XRF analysis of actual soil samples decreased from 51.02% to 5.21%. -
Key words:
- portable X-ray fluorescence spectrometry /
- soil /
- heavy metal /
- iron /
- chromium /
- matrix effect
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表 1 p-XRF仪器工作条件
Table 1. Working parameters of the p-XRF instrument
元素 分析线 准直器(μm) 探测器 电压(kV) 电流(mA) 采样间隔(keV) Cr Kα 150 SDD 45 0.2 0.02 Fe Kα 150 SDD 45 0.2 0.02 注:采样间隔即分辨率,表示每0.02keV能量记录一次荧光强度。 表 2 ICP-OES仪器工作条件
Table 2. Working parameters of the ICP-OES instrument
工作参数 设定条件 射频功率 1150W 冷却气(Ar)流量 12.0L/min 辅助气(Ar)流量 0.5L/min 雾化气(Ar)流量 0.70L/min 样品泵冲洗泵速 100r/min 分析泵速 50r/min 泵稳定时间 5s 总采集时间 20s 表 3 两种校正方法的准确度对比
Table 3. Comparison of accuracy of two correction methods
样品编号 Cr(mg/kg) 相对误差(%) Cr(mg/kg) 相对误差(%) ICP-OES法 p-XRF一维线性回归校正结果 ICP-OES法 p-XRF本法校正结果 硅藻土-1 1154.19 858.27 25.64 1154.19 1135.85 1.59 硅藻土-2 597.17 493.38 17.38 597.17 602.00 0.81 硅藻土-3 1424.00 1407.47 1.16 1424.00 1446.26 1.56 硅藻土-4 890.00 991.73 11.43 890.00 897.22 0.81 硅藻土-5 301.28 464.25 54.09 301.28 277.72 7.82 平均预测相对误差(%) 21.94 平均预测相对误差(%) 2.52 样品编号 Cr(mg/kg) 相对误差(%) Cr(mg/kg) 相对误差(%) ICP-OES法 p-XRF一维线性回归校正结果 ICP-OES法 p-XRF本法校正结果 潮土 37.56 -29.22 177.80 37.56 38.61 2.80 黑土 352.86 270.48 23.35 352.86 375.43 6.39 砖红壤 719.81 931.76 29.45 719.81 752.27 4.51 黄棕壤 1238.13 1102.35 10.97 1238.13 1341.72 8.37 水稻土 1517.97 1312.55 13.53 1517.97 1578.04 3.96 平均预测相对误差(%) 51.02 平均预测相对误差(%) 5.21 -
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