Consiglio Nazionale delle Ricerche (CNR), Istituto di Chimica dei Composti Organometallici, UOS di Pisa, Via Moruzzi 1, 56124 Pisa, Italy.
National Research Council of Canada, 1200 Montreal Road, K1A0R6 Ottawa, Ontario, Canada.
Anal Chim Acta. 2017 Aug 8;980:33-40. doi: 10.1016/j.aca.2017.04.053. Epub 2017 May 16.
In this study we present a novel isotope dilution gas chromatography method for the determination of nitrate in vegetables. The analyte was extracted in water at 70C and mixed with N isotopically enriched nitrate internal standard. The sample was centrifuged and the supernatant reacted with sulfamic acid for removal of nitrite, and with triethyloxonium tetrafluoroborate for converting nitrate into volatile EtONO. This simple aqueous chemistry allowed for separation of analyte from sample matrix in the form of a gaseous derivative which could be sampled in the headspace before GC-MS analysis. This key-feature of the method made possible the collection of clean chromatograms within an elution time of only 1.8 min. Detection of EtONO could be performed using electron impact ionization with a standard GC-MS setup. The method was optimized and validated for the analysis of nitrate in fresh vegetables in the 10-10,000 μg/g range with a detection limit of 2 μg/g. Due to the use of primary isotope dilution quantitation, traceable results of high-precision were attained.
在本研究中，我们提出了一种新颖的同位素稀释气相色谱法，用于测定蔬菜中的硝酸盐。分析物在 70°C 的水中提取，并与 N 同位素富集的硝酸盐内标混合。样品离心后，用氨基磺酸去除亚硝酸盐，用三乙氧氧硼烷四氟硼酸酯将硝酸盐转化为挥发性的 EtONO。这种简单的水相化学方法可以将分析物从样品基质中以气态衍生物的形式分离出来，然后在 GC-MS 分析前在顶空部分取样。该方法的关键特点使得在仅 1.8 分钟的洗脱时间内可以收集到干净的色谱图。使用标准的 GC-MS 装置，通过电子轰击电离可以检测到 EtONO。该方法经过优化和验证，可用于新鲜蔬菜中 10-10,000μg/g 范围内的硝酸盐分析，检测限为 2μg/g。由于采用了一级同位素稀释定量，因此可获得高精度的可溯源结果。
