Kristiansen Jesper, Petersen Henning W
The National Institute of Occupational Health, Lersø Parkallé 105, DK-2100 Copenhagen, Denmark.
J Anal Toxicol. 2004 Sep;28(6):456-63. doi: 10.1093/jat/28.6.456.
An uncertainty budget was constructed for the measurement of ethanol in blood by headspace gas chromatography. The uncertainty budget, covering the analytical range of ethanol concentrations up to 3.00 g/kg, included analytical uncertainty components, traceability uncertainty components, and effects caused by interindividual variation in blood water content. The analytical combined standard uncertainty was estimated from duplicate measurements of real samples and included contributions from headspace recovery, variation between columns, injection, repeatability of analytical signals, and statistical uncertainty of the calibration function. The traceability uncertainty was estimated in a sub-budget based on information about the calibrator and about the preparation of the aqueous standards. Two uncertainty components depended on the interindividual variation in blood water content. First, it caused uncertainty on the density of the blood, and second, it had an effect on the gas phase concentration of ethanol when doing the headspace sampling. These effects as well as their covariance were included in the uncertainty budget. For fresh blood samples, the analytical uncertainty was the dominating uncertainty component, accounting for approximately 90% of the variance. For blood samples collected 100 h postmortem, the interindividual variation in blood water content was the largest uncertainty component. It was demonstrated that subtracting a "safety margin" of 0.1 g/kg from the results was sufficient to keep the risk of committing a type 1 error below 0.1% in ethanol concentrations ranging up to 2 g/kg for fresh blood samples. This risk was higher for postmortem blood samples because of the higher uncertainty of measurement, but still less than approximately 1.4%.
通过顶空气相色谱法测定血液中乙醇含量构建了不确定度预算。该不确定度预算涵盖了乙醇浓度高达3.00 g/kg的分析范围，包括分析不确定度分量、可追溯性不确定度分量以及个体间血液含水量差异所导致的影响。分析合成标准不确定度是根据实际样品的重复测量估算得出的，包括顶空回收率、色谱柱间差异、进样、分析信号重复性以及校准函数的统计不确定度等方面的贡献。可追溯性不确定度是在一个子预算中根据校准物和水溶液标准品制备的相关信息进行估算的。有两个不确定度分量取决于个体间血液含水量的差异。首先，它导致血液密度存在不确定度；其次，在进行顶空进样时，它对乙醇的气相浓度有影响。这些影响及其协方差均包含在不确定度预算中。对于新鲜血液样本，分析不确定度是主要的不确定度分量，约占方差的90%。对于死后100小时采集的血液样本，个体间血液含水量的差异是最大的不确定度分量。结果表明，对于新鲜血液样本，在乙醇浓度高达2 g/kg时，从结果中减去0.1 g/kg的“安全裕度”足以将犯一类错误的风险保持在0.1%以下。对于死后血液样本，由于测量不确定度较高，该风险更高，但仍小于约1.4%。
