电位滴定法测量白酒中总酸含量的不确定度评定

Influence of Distillation to the Content of Phthalate Acid Esters in Liquor

按照GB/T 10345-2007《白酒分析方法》,使用自动电位滴定仪测定白酒中的总酸含量。建立电位滴定法测定白酒中总酸含量的数学模型,对模型中的各参数进行不确定度来源分析,分别进行不确定度A类评定和不确定度B类评定,然后将各不确定度分量进行合成,到白酒中总酸含量的不确定度。结果:白酒中总酸含量测定结果的合成不确定度为0.0018g/L。样品中总酸测量值为0.3838g/L,其扩展不确定度为0.0036g/L(k=2),测量结果可表示为(0.384±0.0036)g/L。滴定消耗标准溶液体积不确定度分量的影响最大,主要来源在于自动电位滴定仪自带滴定管的体积误差、自动电位滴定仪终点识别的误差。在检验过程中,可以通过相关控制措施例如定期对电位滴定仪进行检定来减少不确定度。

According to GB/T 10345-2007 "Method of Analysis for chinese spirits", the total acid content in baijiu was determined by automatic potentiometric titrator. A mathematical model was established for evaluating the uncertainty for the determination of total acid content in baijiu by potentiometric titration. The uncertainty sources of the parameters in the model were analyzed,and evaluted with the uncertainty evaluation of type A or type B. And then the uncertainty of total acid content in baijiu was obtained by synthesizing the components. Results The combined standard uncertainty of total acid content in baijiu was 0.0018 g/L. The expanded uncertainty was0.0036 g/L(k=2)as total acid content in baijiu was 0.3838 g/L. The sample result was expressed as(0.3838±0.0036) g/L(k=2). Conclusion According to the evaluation, volume error from burette and the error of endpoint identification of automatic potentiometric titrator were the main sources for uncertainty. In daily inspection, The automatic potentiometric titrator must be checked and measured regularly.