Effects of Iron-Calcium and Organic Matter Matrix on Cadmium Detection in Soil by Energy Dispersive X-Ray Fluorescence Spectroscopy
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摘要:
镉(Cd)是一种有毒有害重金属，能量色散X射线荧光光谱(EDXRF)技术被广泛应用于检测污染土壤中Cd含量。然而，土壤中的共存元素和有机质等基体组分可能通过X射线的吸收增强、谱线重叠或散射效应干扰Cd检测结果，当前土壤不同组分对检测结果的影响尚未得到充分研究，对仪器的检测精度和准确性构成挑战。本文以硅藻土为基质，分别添加不同浓度的铁(Fe)、钙(Ca)和腐植酸，评估这些成分对Cd荧光信号的干扰情况，并探讨仪器本身的重叠干扰扣除和校正方法在不同元素含量条件下对Cd荧光强度的影响。结果表明，土壤基质中Fe、Ca的大量存在(＞5%)会通过元素间吸收效应导致Cd的EDXRF测定值被低估，而腐植酸的大量存在(＞10%)则会抬高光谱图中的低能散射背景，增加了低浓度Cd的测定误差。基于正交试验设计，引入Fe、Ca及腐植酸作为校正因子，建立了一种多元线性回归的校正模型，通过该模型显著提高了EDXRF测定土壤样品Cd含量的精度，Cd含量测定值与标准值的平均相对误差在未校正情况下的20.67%降至校正后的7.64%。本研究通过合理的校正措施能够显著提升EDXRF技术在不同类型土壤中的应用潜力，为环境监测提供了一种高效、便捷、准确的检测手段。
Abstract:Cadmium (Cd) is a toxic and harmful heavy metal, and energy dispersive X-ray fluorescence spectroscopy (EDXRF) technology is widely used to detect Cd content in contaminated soil. However, matrix components such as coexisting elements and organic matter in soil may interfere with Cd detection results through X-ray absorption enhancement, spectral line overlap or scattering effect, and the influence of different soil components on the detection results has not been fully studied, which poses a challenge to the detection precision and accuracy of the instrument. Different concentrations of iron (Fe), calcium (Ca) and humic acid were added to diatomite as the matrix to evaluate the interference of these components on the Cd fluorescence signal, and the effects of overlapping interference deduction and correction methods on the Cd fluorescence intensity under different element content conditions were discussed. The results showed that the presence of Fe and Ca in the soil matrix (>5%) could lead to the underestimation of the EDXRF measurement of Cd through the inter-element absorption effect, while the presence of humic acid (>10%) could raise the low-energy scattering background in the spectral pattern and increase the determination error of low-concentration Cd. Based on the orthogonal experimental design, Fe, Ca and humic acid were introduced as correction factors, and a multiple linear regression correction model was established, which significantly improved the accuracy of EDXRF in determining Cd content in soil samples. The average relative error between the measured value of Cd content and the standard value decreased from 20.67% without correction to 7.64% after correction. This study demonstrates that the application potential of EDXRF technology in different types of soil through reasonable correction measures can be significantly improved, and an efficient, convenient and accurate detection method for environmental monitoring can be established.
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表 1 正交设计Fe、Ca及腐植酸添加试验
Table 1. Orthogonal design of Fe, Ca and humic acid addition tests
样品编号 Fe添加量
(%)Ca添加量
(%)腐植酸添加量
(%)Cd添加量
(mg/kg)ZJ-1 3 3 1 0.3 ZJ-2 3 5 2.5 0.6 ZJ-3 3 7 5 1.5 ZJ-4 3 9 10 3 ZJ-5 3 11 20 6 ZJ-6 5 3 2.5 1.5 ZJ-7 5 5 5 3 ZJ-8 5 7 10 6 ZJ-9 5 11 1 0.6 ZJ-10 5 9 20 0.3 ZJ-11 7 3 5 6 ZJ-12 7 5 10 0.3 ZJ-13 7 7 20 0.6 ZJ-14 7 9 1 1.5 ZJ-15 7 11 2.5 3 ZJ-16 10 3 10 0.6 ZJ-17 10 5 20 1.5 ZJ-18 10 7 1 3 ZJ-19 10 9 2.5 6 ZJ-20 10 11 5 0.3 ZJ-21 13 3 20 3 ZJ-22 13 5 1 6 ZJ-23 13 7 2.5 0.3 ZJ-24 13 9 5 0.6 ZJ-25 13 11 10 1.5 
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表 2 Fe添加组样品均匀性验证结果
Table 2. Verification of the uniformity in the Fe addition group
Fe含量
(%)RSD(%) Cd浓度
0.3mg/kgCd浓度
0.6mg/kgCd浓度
1.5mg/kgCd浓度
3.0mg/kgCd浓度
6.0mg/kg3 5.24 8.13 6.82 3.75 6.70 5 8.95 2.23 2.45 3.44 1.77 7 1.37 3.34 1.48 1.74 2.50 9 4.15 7.39 6.05 0.68 1.69 11 2.79 0.66 2.64 1.27 0.39 13 8.12 4.03 0.63 1.34 2.36 注：Ca、腐植酸添加组及正交添加组检测结果的RSD均小于10%。
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表 3 正交试验组样品中镉的添加值和EDXRF测定值
Table 3. Cadmium addition and measured values by EDXRF in the orthogonal test group
样品编号 Cd添加值
(mg/kg)Cd测定值
(mg/kg)相对误差
(%)样品编号 Cd添加值
(mg/kg)Cd测定值
(mg/kg)相对误差
(%)ZJ-1 0.30 0.25 17.3 ZJ-14 1.50 1.40 6.7 ZJ-2 0.60 0.55 8.4 ZJ-15 3.00 2.86 4.8 ZJ-3 1.50 1.44 4.0 ZJ-16 0.60 0.45 24.7 ZJ-4 3.00 2.93 2.3 ZJ-17 1.50 1.33 11.1 ZJ-5 6.00 5.92 1.3 ZJ-18 3.00 2.89 3.8 ZJ-6 1.50 1.50 0.3 ZJ-19 6.00 5.87 2.2 ZJ-7 3.00 3.08 2.8 ZJ-20 0.30 0.22 28.1 ZJ-8 6.00 5.83 2.8 ZJ-21 3.00 2.80 6.6 ZJ-9 0.60 0.54 9.8 ZJ-22 6.00 5.94 1.0 ZJ-10 0.30 0.20 32.1 ZJ-23 0.30 0.15 50.5 ZJ-11 6.00 5.87 2.2 ZJ-24 0.60 0.44 26.8 ZJ-12 0.30 0.24 21.7 ZJ-25 1.50 1.25 23.4 ZJ-13 0.60 0.44 26.2
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表 4 样品信息及Cd含量校正前后的准确度对比
Table 4. Sample information and comparison of accuracy before and after Cd content calibration
土壤标准物质
和实际样品Cd含量
(mg/kg)Fe含量
(%)Ca含量
(%)SOM
(%)直接测试结果 模型校正结果 Cd含量
(mg/kg)相对误差
(%)Cd含量
(mg/kg)相对误差
(%)GBW07401 4.3±0.4 4.62 1.23 3.17 4.40 2.33 4.43 2.97 GBW07404 0.35±0.06 7.52 0.19 1.09 0.28 20.0 0.32 7.43 GBW07405 0.45±0.06 8.86 0.07 0.56 0.35 22.2 0.41 9.26 GBW07311 2.3±0.2 3.39 0.47 / 2.42 5.22 2.41 4.75 GBW07312 4.0±0.3 4.34 1.16 / 4.14 3.50 4.15 3.73 砖红壤 0.16 13.5 0.09 2.35 0.02 87.5 0.15 6.25 紫色土 3.07 10.9 1.78 3.42 2.91 8.30 3.02 1.34 灰钙土 0.84 3.17 7.29 1.43 0.72 14.2 0.77 8.51 暗棕壤 0.35 4.13 0.97 13.4 0.26 25.7 0.32 7.94 棕壤 0.25 3.13 0.72 2.22 0.18 28.0 0.17 30.6 注：采用酸消解结合ICP-MS法测定非国标样品中Cd、Fe、Ca全量，采用重铬酸钾外加热氧化滴定法测定非国标样品中有机质含量。
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