Department of Chemistry , Georgetown University , Washington , District of Columbia 20057 , United States.
DSM Nutritional Products , Columbia , Maryland 21045 , United States.
Anal Chem. 2019 Mar 19;91(6):3773-3777. doi: 10.1021/acs.analchem.8b05851. Epub 2019 Feb 28.
Fluorine elemental analysis using inductively coupled plasma mass spectrometry (ICPMS) is challenging because of low F ionization efficiency in the plasma and severe isobaric interferences. Notably, there is an increasing demand for ppb level fluorine measurements due to the rising importance of fluorinated compounds in pharmaceutical, environmental, and food analyses. Here, we report a new elemental ionization method where fluorinated analytes are introduced into an ICP to produce NaF followed by NaF formation in the atmospheric-pressure plasma afterglow. The new method offers over 2 orders of magnitude improved sensitivities (180-500 cps/ppb versus 1.6-3.2 cps/ppb) for F detection. This approach also yields compound-independent F response for quantitation without compound-specific standards. Detection limits of ∼50 ppb F are attained using a single-quadrupole instrument without discrimination against isobaric interferences. Similar LODs are achievable only by isobaric interference reduction in ICPMS/MS. Importantly, the new approach offers facile interfacing to molecular MS instruments where LODs can be further improved via MS/MS and high-resolution MS techniques. The tolerance to matrix is demonstrated by quantitation of fluoride in infant formula, yielding recoveries of 86%-98% with repeatabilities of 3.5-6.3 RSD%.
使用电感耦合等离子体质谱法（ICPMS）进行元素氟分析具有挑战性，这是因为在等离子体中氟的电离效率低，且存在严重的同量异位素干扰。值得注意的是，由于含氟化合物在药物、环境和食品分析中的重要性日益增加，人们对 ppb 级别的氟测量需求不断增加。在这里，我们报告了一种新的元素电离方法，其中将氟化分析物引入 ICP 中以产生 NaF，然后在常压等离子体余晖中形成 NaF。新方法提供了超过 2 个数量级的灵敏度改进（180-500 cps/ppb 与 1.6-3.2 cps/ppb），用于 F 检测。该方法还提供了无需化合物特异性标准品即可进行定量的与化合物无关的 F 响应。使用单四极杆仪器，无需对同量异位素干扰进行区分，即可达到约 50 ppb F 的检测限。在 ICPMS/MS 中仅通过同量异位素干扰减少才能达到类似的 LOD。重要的是，新方法可轻松与分子 MS 仪器接口，通过 MS/MS 和高分辨率 MS 技术，可进一步提高 LOD。通过对婴儿配方奶粉中氟化物的定量，证明了该方法对基质的耐受性良好，回收率为 86%-98%，重复性为 3.5-6.3 RSD%。
