Morrison Kelsey A, Clowers Brian H
Washington State University, Pullman, WA, 99164, USA.
Rapid Commun Mass Spectrom. 2018 Aug 30;32(16):1363-1371. doi: 10.1002/rcm.8177.
A key aspect of detecting hazardous compounds at ultra-trace levels for processing, compliance, and clean-up purposes involves developing methods that are not only sensitive, but also highly selective with minimal sampling effort. Atmospheric flow tube mass spectrometry (AFT-MS) using dielectric barrier discharge ionization has emerged as a technique that combines such features for vapor detection. AFT-MS is thus appealing for application to ambient screening for chemical warfare agents (CWAs) and their degradation products. Initial characterization of AFT-MS for CWA detection necessitates examining less harmful simulant species. A predominant hydrolysis product of most organophosphorus CWAs is methylphosphonic acid and most other hydrolysis products consist of some form of an alkylphosphonic acid.
An application of AFT-MS is presented wherein a homologous series of four alkylphosphonic acids (methyl-, ethyl-, propyl-, and t-butylphosphonic acid) were first qualitatively evaluated as anionic clusters with nitrate. These anionic adducts were subsequently quantified from non-equilibrium headspace vapor sampled over alkylphosphonic acid solutions in methanol.
The series of phosphonic acids demonstrated consistent relative ion abundances thought to be related at least in part to the relative vapor pressures depending on their alkyl chains. For quantitation, the resulting linear ranges were found to be 2 to 50 ppm for methylphosphonic acid, 5 to 50 ppm for ethylphosphonic acid, and 2 to 25 ppm for propylphosphonic acid and t-butylphosphonic acid; quality controls of 15 ppm were used to assess the quantitation accuracy.
Although measured over a limited dynamic range, the real-time analysis afforded by this method suggests the feasibility of using thermodynamically stable anionic adducts to monitor organophosphorus compounds via AFT-MS. In addition, this is proof-of-concept for the use of this ambient sensing technique to detect phosphonic acids. Furthermore, a discussion is included regarding gaps in clustering thermodynamics literature that would assist in uncovering physical or chemical explanations for observed trends.
为了进行处理、合规性检查和清理，检测超痕量水平的有害化合物的一个关键方面是开发不仅灵敏，而且采样量最小且具有高选择性的方法。使用介质阻挡放电电离的大气流动管质谱法（AFT-MS）已成为一种结合这些特性进行蒸汽检测的技术。因此，AFT-MS在化学战剂（CWA）及其降解产物的环境筛查应用中具有吸引力。对用于CWA检测的AFT-MS进行初步表征需要检测危害较小的模拟物。大多数有机磷化学战剂的主要水解产物是甲基膦酸，大多数其他水解产物由某种形式的烷基膦酸组成。
介绍了AFT-MS的一种应用，其中首先对四种烷基膦酸（甲基膦酸、乙基膦酸、丙基膦酸和叔丁基膦酸）的同系物系列作为硝酸盐阴离子簇进行了定性评估。随后，从甲醇中烷基膦酸溶液上方的非平衡顶空气体中对这些阴离子加合物进行了定量分析。
该系列膦酸表现出一致的相对离子丰度，认为这至少部分与取决于其烷基链的相对蒸气压有关。对于定量分析，发现甲基膦酸的线性范围为2至50 ppm，乙基膦酸为5至50 ppm，丙基膦酸和叔丁基膦酸为2至25 ppm；使用15 ppm的质量控制来评估定量准确性。
尽管在有限的动态范围内进行了测量，但该方法提供的实时分析表明，利用热力学稳定的阴离子加合物通过AFT-MS监测有机磷化合物是可行的。此外，这证明了使用这种环境传感技术检测膦酸的概念验证。此外，还讨论了聚类热力学文献中的空白，这将有助于揭示观察到的趋势的物理或化学解释。
