离子色谱法测定奶粉中蛋白质氮、钠、钾、钙及镁

IC Determination of Protein Nitrogen and Na,K,Ca,Mg in Milk Powder

提出了用离子色谱法测定奶粉中蛋白质氮、钠、钾、钙及镁。用浓硫酸及过氧化氢处理样品使完全炭化并氧化,从而得到一无色透明样品溶液。将此溶液继续加热蒸发至1 mL以下,加入一定量的氢碘酸与溶液中硫酸作用,而产生碘及二氧化硫。此两反应产物在150℃温度下加热时从溶液中挥发除去。通过上述处理使溶液的酸度控制在pH 1.5-7之间,使溶液通过IonpacCS12A色谱柱并采用20 mmol·L^-1甲烷磺酸作为淋洗液达到Na^＋、NH4^＋、K^＋、Mg^2＋及Ca^2＋的分离。采用电导检测器进行测定。方法的检出限（3S/N）为0.3-5.0 mg·kg^-1。对方法的回收率及精密度作试验,测定回收率为95.0%-102.0%;相对标准偏差（n=6）为1.1%-3.7%。

Ion chromatography was applied to the determination of protein nitrogen and Na＋,K＋,Ca2＋ and Mg2＋ in milk powder.The sample was digested with conc.H2SO4 and H2O2,to char and oxidize the sample completely and to obtain a colorless and transparent solution which was further evaporated to less than 1 mL.Definite amount of HI acid was added to react with H2SO4 of the solution to produce iodine and sulfur dioxide which were expelled from the solution at the heating temperature（150 ℃）.The acidity of sample solution was brought to pH 1.5-7 by the above operation.Ionpak CS12A column was used for separation of Na^＋,NH4^＋,K^＋,Mg^2＋ and Ca^2＋ in the sample solution,using 20 mmol·L^-1 CH4SO4 as eluent.Conductivity detection was adopted in the determination.Detection limits（3S/N） found were in the range of 0.3-5.0 mg·kg^-1.Recovery and precision of the method were tested,and the values of average recovery found were in the range from 95.0% to 102.0%,with values of RSD′s（n=6） ranged from 1.1% to 3.7%.