微生物法测定乳粉中叶酸的不确定度评定

目的评定微生物法测定乳粉中叶酸的不确定度。方法按照GB 5009.211—2014《食品安全国家标准食品中叶酸的测定》规定的微生物法对婴儿配方乳粉中叶酸含量进行测定,根据CNAS-CL01-G003:2019要求,依据GB/Z22553—2010和JJF1059.1—2012,分析测定过程中影响检验结果的因素主要包括测量重复性、试样前处理(称量、稀释)、标准物质、标准溶液配制(称量、稀释)、实验温度、拟合标准曲线、紫外分光光度计,通过对各个不确定度分量进行分析、评估,计算合成得出被测样品中叶酸含量测量结果的标准不确定度,得出扩展不确定度。结果经测定,婴儿配方乳粉中叶酸含量为(80.2±4.28)μg/100 g,k=2。结论微生物因素对测量不确定度具有显著影响,由标准曲线拟合和重复测量体现。

Uncertainty evaluation for the determination of folic acid in milk powder by microbiological methods

Objective To evaluate the uncertainty for the determination of folic acid in milk powder by microbiological methods.Methods The folic acid content in infant formula milk powder was determined by microbial method according to GB 5009.211—2014 National food safety standard-Determination of folic acid in foods.According to the requirements of CNAS-CL01-G003:2019,GB/Z 22553—2010 and JJF 1059.1—2012,the factors influencing the test results in the analysis and determination process mainly included measurement repeatability,sample pretreatment(weighing and dilution),reference materials,standard solution preparation(weighing and dilution),experimental temperature,standard curve fitting and UV spectrophotometer,through the analysis and evaluation of each uncertainty component,the standard uncertainty of measurement results of folic acid content in the tested sample was calculated and synthesized,and the expanded uncertainty was obtained.Results The content of folic acid in infant formula milk powder was(80.2±4.28)μg/100 g,k=2.Conclusion Microbial factors have significant influence on measurement uncertainty,which is reflected by standard curve fitting and repeated measurement.