关于GB/T 21704-2008方法改进和适用范围的研究

Research on the improvement and application scope of GB/T 21704-2008 method

中文关键词:  乳粉  非蛋白氮  三氯乙酸  三聚氰胺  溶解度  仪器检测限

英文关键词:milk powder  non-protein nitrogen  trichloroacetic acid  melamine  solubility  limit of instrument

中文摘要:

      目的 改进GB/T 21704-2008《乳与乳制品中非蛋白氮含量的测定》中前处理部分提出的方法, 明确方法的适用范围。方法 分别用10、20、30、40、50 mL三氯乙酸溶液沉淀10 mL样品中的蛋白质, 过滤后测定滤液中非蛋白氮含量; 加入10 mL水分别溶解2、4、8 mg三聚氰胺, 分组加入7、8、9 mL三氯乙酸溶液, 观察三聚氰胺在不同浓度三氯乙酸溶液中的析出情况; 10 g样品中分别加标1、2、5、10、20 mg三聚氰胺, 测定计算回收率确定仪器的检测限。结果 样品中蛋白质含量低于20 g/100 g时, 20 mL 15%三氯乙酸溶液可完全沉淀样品中蛋白质; 三聚氰胺在三氯乙酸溶液中会逐渐析出, 且三氯乙酸浓度越高, 三聚氰胺溶解度越小, 越容易析出; 本实验中所用定氮仪最低可准确稳定检测2 mg三聚氰胺/10 g样品。结论 方法改进后沉淀剂用量减半, 可以节约试剂, 在消化环节缩短加热时间, 提高实验效率; 三聚氰胺在三氯乙酸溶液中的溶解度情况和仪器检测限的限制框定方法的适用范围是2~20 mg三聚氰胺/10 g样品。

英文摘要:

      Objective To improve the method proposed in the pretreatment part of GB/T 21704-2008 Determination of non-protein nitrogen in milk and dairy products, and to clarify the scope of application of the method. Methods The protein in 10 mL samples was precipitated with 10, 20, 30, 40 and 50 mL trichloroacetic acid solutions, and the content of non-protein nitrogen in the filtrate was determined after filtration. The 10 mL water was added to dissolve 2, 4 and 8 mg of melamine, respectively, and 7, 8 and 9 mL of trichloroacetic acid solutions were added in groups to observe the precipitation of melamine in trichloroacetic acid solutions of different concentrations. The 1, 2, 5, 10, 20 mg of melamine were spiked in 10 g samples, and the detection limit of the instrument was determined by determination and calculation of recovery rates. Results When the protein content in the sample was less than 20 g/100 g, 20 mL of 15% trichloroacetic acid solution could completely precipitate the protein in the sample. Melamine would gradually precipitate in the trichloroacetic acid solution, while the concentration of trichloroacetic acid get higher, the solubility of melamine would get lower and the easier it was to precipitate. The nitrogen analyzer used in this experiment could accurately and stably detect 2 mg melamine /10 g samples at the minimum. Conclusion After the method is improved, the amount of precipitant is reduced by half, which can save reagents, shorten the heating time in the digestion process, and improve the efficiency of the experiment. The solubility of melamine in trichloroacetic acid solution and the restriction of the instrument detection limit are applicable to 2-20 mg melamine /10 g samples.