Rädlinger G, Heumann K G
Institute of Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg-University, Mainz, Germany.
Anal Chem. 1998 Jun 1;70(11):2221-4. doi: 10.1021/ac971308k.
Two different sample treatment methods are used in connection with inductively coupled plasma isotope dilution mass spectrometry for accurate and precise determinations of iodine traces in food samples. 129I-enriched iodate is applied as a spike compound for the isotope dilution step. Extraction of iodine by tetramethylammonium hydroxide (TMAH) solution at high temperatures in a closed vessel is one of the sample treatment methods. The other one is a complete decomposition of the sample with a mixture of perchloric acid and nitric acid using microwave assistance. By analyzing different certified reference materials (three milk powders with different iodine levels, BCR CRM 63, 150, and 151; bovine liver BCR CRM 185), the accuracy of ICP-IDMS with both sample treatment methods could be demonstrated. The relative standard deviation was typically in the range of 0.6-2.8% for iodine concentrations between 0.1 microgram g-1 and 5 micrograms g-1. The detection limit was 8 ng g-1 using sample weights of 0.8 g. In a round robin test, using two different types of infant food samples, the results of the two ICP-IDMS methods and of an ICP-MS method without the isotope dilution technique, but applying the TMAH extraction procedure, agree very well with the mean of results of all participating laboratories also using ICP-MS/TMAH. However, the ICP-IDMS method is faster, more precise, widely independent of matrix effects, and, therefore, relatively accurate, which makes this method especially attractive for use as a routine method.
电感耦合等离子体质谱同位素稀释法用于准确测定食品样品中的痕量碘时,采用了两种不同的样品处理方法。富集129I的碘酸盐用作同位素稀释步骤的加入化合物。在密闭容器中用氢氧化四甲铵(TMAH)溶液在高温下萃取碘是其中一种样品处理方法。另一种方法是在微波辅助下用高氯酸和硝酸的混合物将样品完全分解。通过分析不同的标准参考物质(三种不同碘含量的奶粉,BCR CRM 63、150和151;牛肝BCR CRM 185),可以证明两种样品处理方法的电感耦合等离子体质谱同位素稀释法的准确性。对于0.1微克/克至5微克/克之间的碘浓度,相对标准偏差通常在0.6%-2.8%范围内。使用0.8克样品重量时,检测限为8纳克/克。在一次循环试验中,使用两种不同类型的婴儿食品样品,两种电感耦合等离子体质谱同位素稀释法以及一种未采用同位素稀释技术但应用TMAH萃取程序的电感耦合等离子体质谱法的结果,与所有参与实验室同样使用电感耦合等离子体质谱/TMAH法的结果平均值非常吻合。然而,电感耦合等离子体质谱同位素稀释法速度更快、更精确,基本不受基质效应影响,因此相对准确,这使得该方法特别适合用作常规方法。