Discussion onthe Data Drift Correction Method in Homogeneity Assessment of Environmental Reference Materials
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摘要: 均匀性检验是环境标准样品研制的重要技术环节，在均匀性检验过程中，数据漂移对环境标准样品均匀性判定及其不确定度评定的影响不容忽视。本文结合实例，从实验方案和数理统计方法等方面探讨了随机分析法、随机区组法、内插校正法、趋势分析校正法等均匀性检验实验方案及数据漂移校正方法。提出采用t检验法判断数据漂移的显著性，在数据漂移趋势不显著的情况下，采用随机分析法进行标准样品的均匀性检验。在数据漂移显著的情况下，宜采用内插校正法或趋势分析校正法对均匀性数据进行漂移校正。以某土壤中Ni元素均匀性检验为例，经采用内插校正法和趋势分析校正法校正漂移数据后，测量值的相对标准偏差(RSD)由3.0%分别下降为1.4%和1.2%，直线模型斜率的绝对值由0.2003 mg/kg分别下降为0.02870mg/kg和4.709×10-5mg/kg。土壤中Ni、Cu、Co、Tl等4种重金属元素的瓶间均匀性不确定度分量(ubb)与随机分析法相比，下降最高达78%。在长时间分析测试过程中数据漂移校正效果欠佳的情况下，宜采用随机区组法进行标准样品的均匀性检验。Abstract:
BACKGROUNDAssessment of homogeneity of Environmental Reference Material (ERM) is one of the most important steps for the development of an ERM. The data drift has a serious negative effect on the assessment of homogeneity and uncertainty of ERM. OBJECTIVESTo develop the drift correction methods for homogeneity test of ERM. METHODSThe drift correction methods were discussed from the aspects of experimental scheme and statistical methods through practical cases. The drift correction methods, such as random analysis, randomized block design, interpolation correction, and trend analysis correction, were introduced in details. RESULTSThe t-test method was proposed to judge the significance of data drift. For insignificant drift trend, the random analysis method was useful for the evaluation of uncertainty of homogeneity. If the drift trend was significant, better-corrected results were obtained by using interpolation correction and trend analysis correction methods. For example, after data correction by interpolation correction and trend analysis, the relative standard deviation (RSD) of homogeneity data of Ni in soil decreased from 3.0% to 1.1% and 0.84%, respectively. The absolute value of slope of line decreased from 0.2003mg/kg to 0.02870mg/kg and 4.709×10-5mg/kg. The uncertainties of between-bottle homogeneity of Ni, Cu, Co and Tl decreased by 78% compared with the random analysis method. CONCLUSIONSData drift correction methods are not effective for long periods of measurement, therefore the experimental scheme of randomized block design method is recommended for homogeneity study. -
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表 1 土壤中Ni元素漂移校正前后均匀性检验分析结果
Table 1. Homogeneity data of Ni in soil before and after drift correction
分析序列 样品编号① Ni含量(mg/kg) 校正前 内插法 趋势分析法 监控样-1 - 26.4 - - 1 12-2 87.5 87.5 87.5 2 14-1 88.3 88.3 88.5 3 3-2 88.3 88.3 88.7 4 7-1 87.8 87.8 88.4 5 16-1 88.3 88.3 89.1 6 20-2 88.0 88.0 89.0 7 11-1 88.8 88.8 90.0 8 19-1 88.3 88.3 89.7 监控样-2 - 26.0 0.9811② - 9 20-1 89.0 90.7 90.6 10 19-2 86.8 88.5 88.6 11 9-1 89.0 90.7 91.0 12 17-1 88.5 90.2 90.7 13 14-2 88.0 89.7 90.4 14 8-2 88.3 90.0 90.9 15 17-2 87.5 89.2 90.3 16 18-2 88.0 89.7 91.0 监控样-3 - 25.8 0.9678② - 17 2-1 85.5 88.3 88.7 18 10-1 86.5 89.4 89.9 19 12-1 86.0 88.9 89.6 20 10-2 87.0 89.9 90.8 21 6-2 87.0 89.9 91.0 22 6-1 84.5 87.3 88.7 23 1-1 83.5 86.3 87.9 24 1-2 83.8 86.6 88.4 监控样-4 - 25.3 0.9508② - 25 9-2 85.0 89.4 89.8 26 13-2 83.3 87.6 88.3 27 4-1 84.8 89.2 90.0 28 5-2 83.3 87.6 88.7 29 15-1 82.5 86.8 88.1 30 5-1 83.0 87.3 88.8 31 2-2 84.0 88.4 90.0 32 15-2 82.5 86.8 88.7 监控样-5 - 24.9 0.9337② - 33 8-1 82.8 88.7 89.2 34 13-1 82.0 87.8 88.6 35 4-2 81.0 86.8 87.8 36 18-1 81.8 87.6 88.8 37 11-2 84.0 90.0 91.2 38 7-2 83.3 89.2 90.7 39 3-1 82.8 88.7 90.4 40 16-2 80.8 86.5 88.6 监控样-6 - 24.4 - - 注：①样品编号规则为：横线前面数字为瓶号，横线后面为子样编号。如12-2，其中12为第12瓶样品，2为第12瓶第2个子样；②为漂移校正系数。 
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表 2 土壤中4种重金属元素漂移校正前后均匀性检验分析结果比较
Table 2. Comparison of homogeneity data of four heave metals in soil before and after drift correction
元素 直线方程 tcal 校正方法 测量均值(mg/kg) RSD (%) MSb (mg/kg) MSw (mg/kg) F ubb (mg/kg) sr (mg/kg) 随机分析法 85.5 2.2 7.091 6.153 1.15 0.986 2.48 Ni y=-0.2003x+89.6 13.61 趋势分析法 89.4 0.84 1.142 1.108 1.03 0.417 1.05 内插法 88.5 1.1 1.906 0.996 1.91 0.675 0.998 随机分析法 64.0 2.7 5.790 3.136 1.85 1.15 1.77 Cu y=-0.1499x+67.6 12.50 趋势分析法 67.2 1.1 0.2828 0.1525 1.85 0.255 0.391 内插法 66.4 0.92 0.7466 0.4955 1.51 0.354 0.704 随机分析法 31.8 2.3 1.085 0.6270 1.73 0.479 0.792 Co y=-0.05642 x+33.2 9.88 趋势分析法 33.2 1.1 0.2828 0.1525 1.85 0.255 0.391 内插法 32.6 1.2 0.3115 0.1760 1.77 0.260 0.420 随机分析法 3.29 1.5 5.137×10-3 6.555×10-3 0.78 0.0322 0.0810 Tl y=0.005912 x+3.17 12.15 趋势分析法 3.18 0.85 1.466×10-3 1.073×10-3 1.37 0.0140 0.0328 内插法 3.19 0.81 1.347×10-3 8.700×10-4 1.55 0.0154 0.0295
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表 3 随机区组法分析土壤中Pb元素分析结果
Table 3. Analytical results of Pb in soil using a randomized block design method
序号 Pb平行测定结果(mg/kg) 测定平均值(mg/kg) 第1次测试 第2次测试 第3次测试 1 20.5 20.4 19.2 20.0 2 21.2 20.1 19.4 20.2 3 20.4 20.3 19.7 20.1 4 20.2 20.7 19.3 20.1 5 20.2 20.3 19.1 19.9 6 21.3 19.7 19.5 20.2 7 20.7 19.1 19.2 19.7 8 20.3 19.6 19.4 19.8 9 19.8 19.4 19.2 19.5 10 21.2 20.3 19.5 20.3 11 19.9 20.4 19.4 19.9 12 20.0 19.6 19.5 19.7 13 19.6 19.2 19.5 19.4 14 19.5 19.4 19.7 19.5 15 20.7 19.6 19.5 19.9 16 19.8 19.6 19.3 19.6 17 21.2 20.0 19.4 20.2 18 20.3 19.3 19.6 19.7 19 20.4 19.2 19.6 19.7 20 19.8 19.1 19.2 19.4 均值 20.4 19.8 19.4 19.8
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表 4 土壤中Pb元素的双因素无重复方差分析法统计分析结果
Table 4. Statistical results of Pb in soil by two-factor non-repetitive analysis of variance
变异来源 离均差平方和(SS) 自由度 均方(MS) F P Fcrit 瓶间 4.793 19 0.2522 1.47 0.1531 1.87 区组间 9.012 2 4.5061 26.26 6.89×10-8 3.24 瓶内 6.521 38 0.1716 - - - 总计 20.326 59 - - - -
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