Wolff J C, Taylor D P, De Bièvre P
Institute for Reference Materials and Measurements, European Commission-JRC, Geel, Belgium.
Anal Chem. 1996 Sep 15;68(18):3231-7. doi: 10.1021/ac9603688.
An isotope dilution mass spectrometric procedure was developed for the determination of nitrate in water samples. The isotope dilution experiments were carried out using the Institute for Reference Materials and Measurements's 15N-enriched nitrate spike reference material IRMM-627. Nitrate was isolated from the matrix by precipitating it as nitron nitrate, from which emission of negative thermal NO2-ions was found to be best. The ions were produced in the ion source of a small, low-cost, easy-to-handle thermionic quadrupole mass spectrometer equipped with a secondary electron multiplier coupled to an ion counter. The procedure developed was applied to the measurement of nitrate in a certified reference material (stimulated rainwater, CRM 409 from Community Bureau of Reference), in sparkling mineral water, and in tap water. Results were compared with those obtained using ion chromatography. Good agreement (within 1%) was found between the concentration determined by isotope dilution mass spectrometry, the values from ion chromatography, and the certified value. The procedure developed allowed accurate and traceable determinations of nitrate in water samples, with an expanded uncertainty (coverage factor k = 2) of 2-5%, and the detection limit was found to be 2 mumol kg-1.
开发了一种同位素稀释质谱法来测定水样中的硝酸盐。使用参考物质与测量研究所的富含15N的硝酸盐加标参考物质IRMM - 627进行同位素稀释实验。通过将硝酸盐沉淀为硝酸硝来从基质中分离硝酸盐，发现由此产生的负热NO2-离子发射效果最佳。这些离子在一台小型、低成本、易于操作的热离子四极杆质谱仪的离子源中产生，该质谱仪配备了与离子计数器相连的二次电子倍增器。所开发的方法应用于测定有证参考物质（模拟雨水，欧洲标准局的CRM 409）、气泡矿泉水中以及自来水中的硝酸盐。将结果与使用离子色谱法获得的结果进行比较。发现同位素稀释质谱法测定的浓度、离子色谱法的值与认定值之间具有良好的一致性（在1%以内）。所开发的方法能够准确且可溯源地测定水样中的硝酸盐，扩展不确定度（包含因子k = 2）为2 - 5%，并且检测限为2 μmol kg-1。
