双误差回归模型在ICP-MS测定饮用水中锶的不确定度评定的简化应用

在计算电感耦合等离子体质谱法测定饮用水中锶的浓度(x)时,由于标准系列配制和仪器检测过程中信号(y)漂移产生的不确定度会传递给最终的计算结果。普通的一次或多次线性拟合结果不能真实地反映对于x、y值都含误差的数据拟合情况。文章对标准曲线进行了双误差回归计算,从双误差回归线性方程推导出校准曲线拟合过程产生不确定度的计算公式,建立了方法检出限与曲线拟合参数(x、y、曲线截距和斜率)及其相关不确定度之间的关系式,依据误差连续传递公式及不确定度分量计算公式简化了合成不确定度的表达式。从合成不确定度计算公式中可得出,水样中锶含量的浓度越低,其对应的不确定度越大;标准系列配制过程不细致、仪器灵敏度低,方法检出限越差,与实际测试情况符合。

Simplification Application of Two-error Regression Model in the Uncertainty Evaluation on Inductively Coupled Plasma-Mass Spectrometric Determination of Sr in Drinking Waters

This paper introduces the method of double-error regression in the course of standard curve fitting was introduced. The uncertainties of standard solutions and signal shift of the instrument were propagated into the final analytical results of Sr in drinking water by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and by using a continuous propagation model. The fitting results obtained by one time and multi-time linear regression models did not reflect the true result and two different sources of uncertainty. The double-error regression model was applied to the standard work curve reported in this paper. The uncertainty calculation for the standard work curve was derived from the double-error regression equations, which built the relationship among detection limits, parameters for curve regression and associated uncertainties. The equation for total uncertainty was simplified by a continuous propagation model and calculation equations for the uncertainty components. The results indicate that the relative uncertainty of the measurement results is greater when the Sr concentration is lower. It also shows that the value of the detection limit increases and the sensitivity is reduced with the rougher processing for the preparation of a standard series. Both issues above prove that the test result matches the practical situation well.