吹扫捕集气相色谱-质谱法测定土壤中挥发性有机物的测量不确定度评定

Evaluation of Uncertainty in Determining Volatile Organic Compounds in Soil with Purge and Trap/GC-MS

挥发性有机物(VOCs)是污染场地中一类重要有毒有害污染物,开展土壤中VOCs的测量不确定度评定,有助于科学评估场地污染水平及修复效果。本研究通过分析和量化系列标准溶液配制、自动进样器取样、内标物添加、样品测量重复性和平均响应因子(RRF)等5个不确定度分量,得到了合成标准不确定度、扩展不确定度,对吹扫捕集气相色谱-质谱法测定土壤中VOCs的不确定度进行了全面评定并建立了不确定度评定方法。结果表明,当土壤样品VOCs均值为19.60μg/L时,取包含因子k=2(约95%置信概率),扩展不确定度在2.13~9.55μg/L之间。其中,RRF的不确定度分量是本方法不确定度中贡献最大的分量,其次是样品测量重复性的不确定度分量。因此,在土壤VOCs检测中应采取提高配制标准溶液和加入内标的准确度、保持仪器性能稳定、改进前处理程序和提高样品回收率等措施,提高检测精密度。

Volatile organic compounds(VOCs) are important toxic and harmful pollutants in contaminated sites, the measurement uncertainty assessment of VOCs in soil is conductive to evaluate scientifically the pollution levels and remediation effects of contaminated sites. In this study, the combined standard uncertainty and expanded uncertainty were calculated by analyzing and quantifying the relative standard uncertainty of five uncertainty components, including the preparation of a series of standard solutions, automatic sampler sampling, the addition of internal standards, sample measurement repeatability and average relative response factor, and the uncertainties of determination of VOCs in soil using purge and capture gas chromatographymass spectrometry(GC-MS) were comprehensively evaluated, and the uncertainty evaluation method was established. The results showed that the expanded uncertainties were 2.13~9.55 μg/L, when the concentration of VOCs was 19.60 μg/L with the coverage factor k=2(the confidence probability is 95%). The uncertainty component of average relative response factor was the most important component in this uncertainty evaluation method, followed by the uncertainty component of sample measurement repeatability. Therefore, it should be taken to improve the accuracies of preparing standard solution and adding internal standard, to keep the stability of instrument performance, to improve the pretreatment procedure and to increase the recovery rate of sample for improve the precision in the measurement for VOCs in soil.