配方乳粉中碘含量测定方法的适用性

Applicability of methods for determination of iodine in nutrition formula

目的研究电感耦合等离子体质谱法(inductively coupled plasma mass spectrometry,ICP-MS)及气相色谱法(gas chromatography,GC)测定不同基质配方乳粉中碘含量的适用性。方法验证了ICP-MS检测碘的方法在乳粉基质中的线性、精密度、准确度及检出限。对GC法与ICP-MS法检测7种不同基质配方乳粉(普通乳基、低乳糖配方、部分水解蛋白配方、含大豆蛋白配方、高蛋白配方、深度水解蛋白配方与混合蛋白)中碘含量的结果进行了比对,并对检测结果差异原因进行了探讨。结果 ICP-MS方法精密度与准确度良好,操作简单,且适用于不同种类乳品中碘含量的检测。ICP-MS法与GC法的比较结果显示,普通乳基配方中两种方法的检测偏差范围在11%以内;多数特殊医学用途配方食品(foods for special medical purpose,FSMP)中,GC法的检测结果会偏低10%～20%;含有混合蛋白的产品中,GC法的检测结果偏低高达71. 1%。通过ICP-MS法辅助跟踪GC法前处理过程中碘的分布发现,实验样品在处理过程中大部分碘随蛋白沉淀而流失,造成检测结果偏低。结论ICP-MS法较GC法适用性更广,不易受基质干扰,适用于日常检测中对FSMP产品中碘含量的判定。

Objective The applicability of both inductively coupled plasma mass spectrometry (ICP-MS)and gas chromatography (GC)method to accurately determine iodine in dairy products with different matrices was assessed.Methods The performance of ICP-MS iodine method for dairy products has been validated by assessing its linearity, precision,accuracy,limit of detection (LOD)and limit of quantity (LOQ)in various food matrices.Both GC and ICP-MS method were used to determine iodine in samples with 7 different types of matrices,including milk base formula,low lactose formula, partially hydrolyzed protein formula,soy protein contained formula,high protein formula, deeply hydrolyzed protein formula and complete nutrition formula (mixed protein sources).The testing result were compared,and the root cause of the result difference between the two method was further investigated and discussed.Results The ICP-MS method showed a good precision and accuracy in different types of dairy products.The experiments demonstrated that the result differences were less than 11% between two method in milk base formula.The GC result were typically 10%-20% lower than the ICP-MS result in most foods for special medical purpose (FSMP)products.One extreme case occurred in the complete nutrition formula sample,in which the GC result was 71.1% lower than the ICP-MS result.By testing the iodine distribution by ICP-MS after each step of sample preparation of the GC method,most iodine in this formula has been removed during the protein precipitation step,causing the extremely low iodine recovery. Conclusion ICP-MS method is more robust and has larger applicable scope,which is more suitable for the routine test of iodine in FSMP products.