Research on Preparation and Characterization of Nitrate and Nitrite Reference Material in Skim Milk Powder
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KeyWord:reference material  ion chromatography  nitrate  nitrite  milk powder
LI Xiao-cui,LU Xiao-hua*,HU Rong,KAN Ying,GUO Jing,SHI Nai-jie 1.北京化工大学理学院;2.中国计量科学研究院;3.深圳市计量质量检测研究院
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      The sample preparation technique for nitrate and nitrite reference material in skim milk powder was studied and evaluated.A candidate reference material was prepared by matrix spiking and vacuum freeze drying method.The method of acetic acid protein precipitation-solid extraction/ion chromatography with ultra violet detector was used for the assessment of the prepared sample.Compared with the conductivity detector suggested by the national standard method,UV detector could be more efficient in avoiding the co-eluted constituent interference in milk matrix and enhancing detection precision,to meet the requirement for evaluation of preparation recovery,homogeneity and stability of the milk powder sample.The measured values of nitrite and nitrate in sample agreed with the target values of preparation,with recoveries of 91% and 101%,respectively.The assessed relative uncertainties obtained from the in-homogeneity of nitrite and nitrate by analysis of variance were 2.9% and 0.3%,respectively,with the minimum sample intake of 1.0 g.The short-term and long-term stabilities in -20 ℃,dry,vacuum and light-proof packaging conditions were predicted to be satisfactory by isochronous and accelerated stability study at -70,-20,4,20,35, 45 ℃,and linear regression trend analysis.The research demonstrated that it was feasible to develop the milk powder reference material containing nitrate and nitrite.The established sample preparation method could ensure the accuracy of reference materials characterization results.