分光光度法测定牛乳中亚硝酸盐含量的不确定度评定

目的]研究分光光度法测定牛乳中亚硝酸盐含量的不确定度评定。方法]根据《GB 5009.33—2016食品安全国家标准食品中亚硝酸盐与硝酸盐的测定》中的第二法分光光度法来测定牛乳中亚硝酸盐的含量。通过分析不确定度的来源，建立完整的数学模型，对模型中的各个分量进行分析和评定，合成相对标准不确定度，并对合成的相对标准不确定度进行扩展，得出牛乳中亚硝酸盐含量的扩展不确定度。结果]当取置信度为95%时，得到的牛乳中亚硝酸盐含量：X=（0.058±0.0034）mg/kg，取k=2，扩展不确定度为U=0.0034 mg/kg。结论]试验过程的不确定度主要来源于标准工作溶液配制过程、试样处理液总体积、测定样液定容体积和样品的重复性。该方法可以为分光光度法测定牛乳中亚硝酸盐含量的不确定度评定提供参考依据。

Evaluation of Uncertainty for Determination of Nitrite Content in Milk by Spectrophotometry

Objective]To study the uncertainty evaluation of spectrophotometric determination of nitrite content in milk．Method]The nitrite content in milk was determined by the second spectrophotometric method in the Determination of Nitrite and Nitrate in Food of National Food Safety Standard GB 5009.33-2016．By analyzing the source of the uncertainty，a complete mathematical model was established，and each component in the model was analyzed and evaluated．The relative standard uncertainty was synthesized，and the extended uncertainty of the synthetic relative standard uncertainty was obtained．Result]When the confidence was 95%，the nitrite content of milk was X=（0.058±0.0034） mg/kg，k=2，and the extended uncertainty was U=0.0034 mg/kg．Conclusion]The uncertainty of the test process mainly comes from the preparation process of standard working solution，the total volume of sample treatment liquid，the constant volume of test sample liquid and the repeatability of the sample．This method can provide a reference for the determination of the uncertainty of nitrite content in milk by spectrophotometry．