离子色谱法测定原料乳中蛋白质含量

Determination of Proteins in Crude Milk by Ion Chromatography

目的建立测定原料乳中蛋白质的离子色谱法。方法用15%三氯乙酸沉淀原料乳中蛋白并抽滤得滤液,用硫酸—双氧水体系分别消解原料乳及滤液,用20mmol/L的甲烷磺酸作淋洗液,IonpacCS12A色谱柱,DS-6电导检测器测定原料乳及滤液中的NH4+-N含量,两者之差乘以转换系数即为蛋白质含量。结果蛋白质(以NH4+-N计)在0.2～10mg/L范围内线性良好,该方法的定量限为0.038g/100g,加标回收率为90.0%～105.0%,相对标准偏差(RSD)为1.06%～5.38%。结论本法简便、快速、准确,灵敏度及精密度高,适用于原料乳中蛋白质含量的测定。

Objective To develop an ion chromatography method for the determination of protein in raw milk. Method The proteins in raw milk were precipitated by 15 % trichloroacetic acid and then filtered. The raw milk and the filtrate were digested separately by a H2 SO4-H2O2 system. The eluent was 20 mmol/L methanesulfonic acid. The analytical column was Ionpac CS12A and the NH4^＋-N content was detected by DS-6 conductivity detector. The protein content in raw milk was calculated by the difference between the NH4^＋ -N content of raw milk and that of the filtrate, and multiplied by a conversion factor. Results The content of protein calculated by NH4^＋ -N showed a good linearity in the range between 0.2 and 10 mg/L,the limit of quantification was 0.038 g/100 g and the recovery of standard addition was 90.0%-105.0% with relative standard deviation （RSD） of 1.06%- 5.38 %. Conclusion The method was simple, rapid and accurate, and proved to be satisfactory for the determination of protein content in raw milk.