Objective: Characterization and evaluation of the uncertainty of the reference materials of cholesterol in aqueous solution. Methods: The certified reference material GBW09203b was weighed accurately and dissolved into methyl cyclodextrin aqueous solution to prepare six kinds of candidate reference materials of cholesterol according to the concentration. The materials were tested for homogeneity and stability using routine methods and were evaluated the uncertainty derived from the inhomogeneity and instability. The uncertainty due to measurement was derived from the purity of the raw material, the weighing and the density measurement. The certified values and expanded uncertainties were calculated according to the ISO Guide. The expanded uncertainty of the certified value was the combination of standard uncertainty of measurement, inhomogeneity and instability. The coverage factor, k, was determined from the Student's t-distribution corresponding to the calculated effective degrees of freedom and 95% level of confidence. Results: It showed that the six candidate reference materials were homogeneous and were tested to be stable for at least 1 year at -70 ℃ and -20 ℃ using the isochronous stability study. The relative uncertainties due to the inhomogeneity were 0.14%, 0.11%, 0.13%, 0.47%, 0.39% and 0.11%. The relative uncertainty due to the instability was 0.25% at -70 ℃. The uncertainties of measurement were 0.06%, 0.05%, 0.05%, 0.05%, 0.05% and 0.05%.The certified values (reference value ± expanded uncertainty, mmol/L) were as follows: (0.651±0.004), (1.310 ±0.007), (2.574±0.015), (5.210±0.055), (7.710±0.072), (10.242±0.056) mmol/L. Conclusions: Six kinds of certified reference materials for cholesterol in aqueous solution have been prepared, which were homogeneity, stable and reliable. It showed that the uncertainty of measurement was very small compared with the uncertainty due to inhomogeneity and instability.
目的： 对胆固醇水溶液标准物质进行定值和不确定度评定。 方法： 以胆固醇标准物质GBW09203b为原料，称量配制6个浓度水平的环糊精水溶液标准物质。用常规方法进行均匀性和同步稳定性研究，评价不均匀性、不稳定性引入的不确定度。定值过程的不确定度主要来源于样本原料、称量和密度测定。将不均匀性、不稳定性和定值产生的不确定度合成计算总不确定度。 结果： 6个浓度水平胆固醇标准物质由不均匀性引入的相对不确定度分别为0.14%、0.11%、0.13%、0.47%、0.39%和0.11%；－70 ℃下由不稳定性产生的相对不确定度均为0.25%；定值产生的相对不确定度分别为0.06%、0.05%、0.05%、0.05%、0.05%和0.05%。6个浓度水平胆固醇标准物质的认定值(标准值±扩展不确定度)分别为(0.651±0.004)、(1.310 ±0.007)、(2.574±0.015)、(5.210±0.055)、(7.710±0.072)、(10.242±0.056)mmol/L。 结论： 研制的6个浓度水平胆固醇水溶液一级标准物质均匀、稳定，定值可靠。与不均匀性和不稳定性产生的不确定度相比，定值测量产生的不确定度比较小。.
Keywords: Aqueous solution; Cholesterol; Reference material; Uncertainty.