元素分析-稳定同位素质谱同时测定δ^(13)C/δ^(15)N在原料乳粉检验中的应用

Simultaneous Determination of δ^(13)C/δ^(15)N in Raw Milk Powder by Elemental Analysis-Isotope Ratio Mass Spectrometry

建立了元素分析-稳定同位素质谱(EA-IRMS)同时测定原料奶粉中δ13 C/δ15 N的检测方法。该方法稳定性(标准偏差):参考气体δ13 C<0.02‰/δ15 N<0.04‰、实际样品δ13C<0.18‰/δ15 N<0.06‰;线性(斜率):参考气体δ13 C<0.04/δ15 N<0.01,实际样品δ13C<0.04/δ15 N<0.01,长期稳定性能满足以上指标。对来源各异的原料乳粉(含半成品原料、牛初乳粉)持续性的检测结果表明,多种原料乳粉均有各自稳定且差异性显著的δ13 C区间:新西兰(-26‰～-29‰)、澳大利亚(-26‰～-27‰)、美国(-16‰)、丹麦(-22‰～-24‰)、内蒙古(-25‰)、新疆/宁夏(-17‰～-22‰)。同时在半成品原料乳粉中,δ13C值在1段到3段呈现规律性变大的趋势,而δ15 N无明显变化,多集中在6‰～8‰这一区间。对部分原料乳粉中可能非法加入的,用以提高乳粉中氮含量的外源物质进行测定发现,常见化工类高氮化合物如尿素、三聚氰胺δ15 N为负值,与原料奶粉及其他蛋白类高氮物有显著差异。将三聚氰胺作为添加物,按提高蛋白含量10%的比例加入某一原料乳粉中,经过此方法检测,发现其δ15 N从6.344‰降至5.660‰。EA-IRMS技术具有较好的稳定性和重现性,降低了操作难度和成本,可以应用到企业中作为监控原料乳粉来源和质量品质稳定性的方法。

An analytical method was developed for simultaneous determination ofδ13 C/δ15 N in raw milk powder by elmental analysis-isotope ratio mass spectrometry（EA-IRMS）.The precision of the method as follows：reference gasδ13C0.02‰/δ15 N0.04‰,practical samplesδ13 C0.18‰/δ15 N0.06‰;are linear reference gasδ13C0.04/δ15 N0.01,practical samplesδ13 C0.04/δ15 N0.01;the long-term stability performance meet the above indexes.Test results of different sources of raw milk powder（including Semi-finished materials powder and Pure Colostrums Powder）indicated that theδ13 C value interval of many kinds of raw milk is stable and significantly different from each other：New Zealand（-26‰to-29‰）,Australia（-26‰ to-27‰）,America（-16‰）,Denmark（-22‰ to-24‰）,Inner Mongolia（-25‰）,Xinjiang/Ningxia（-17‰to-22‰）.It was also found that theδ13 C value in semi-finished materials powder showed an increasing trend from 1to 3periods,butδ15 N value had no significant change,mostly concentrating in the interval of 6‰to 8‰.Test results of possible additives in milk powder which are used to improve the content of nitrogen in powder materials showed thatδ15 N of common chemical high-nitrogen compounds such as urea and melamine is negative,which was significantly different from raw milk and other products with high nitrogen content.With melamine as additives to increase the proportion of protein content in the milk by 10%,test results showedδ15 N value reduced from 6.344‰ to 5.660‰.The method ofδ13 C/δ15 N-EA-IRMS had excellent stability and repeatability and the operation cost was reduced.It can be used for the monitoring of raw milk source and quality control.