元素分析法测定奶粉中蛋白质含量及氮含量的不确定度评定

Determination of Protein Content in Milk Power by Elemental Analysis and Uncertainty Evaluation of Measurement Result for Nitrogen Content

采用元素分析法测定了奶粉中蛋白质含量,并用实例对元素分析法测定奶粉中氮含量的不确定度进行了评定。不确定度的主要来源为校准曲线的拟合。其他不确定度的来源从大到小依次为测量重复性、标准物质和称量过程。氮含量测定结果的扩展不确定度为0.15%(置信水平P为95%)。为减小不确定度应选用与待测物氮含量尽可能接近的标准物质、增加标准曲线中的实验点数、使用误差小的天平。

The content of protein in milk power was determined by elemental analysis and the uncertainty of the measurement result for nitrogen content was evaluated.The main source of the uncertainty was from the fitting process of standard curve.The other uncertainties were listed as following:the measurement repeatability,standard substance and weighing process.The expanded uncertainty for the measurement result of nitrogen content was 0.15%(the confidence level P is 95%).It is helpful to decrease the uncertainty by choosing the calibration material with N content as close as possible to that of the sample to be measured,increasing the number of experiment points in the standard curve,and using the balance with small error.