Pavlov Julius, Braida Washington, Ogundipe Adebayo, O'Connor Gregory, Attygalle Athula B
Department of Civil, Environmental, and Ocean Engineering, Center for Environmental Systems, Stevens Institute of Technology, Hoboken, New Jersey 07030, USA.
J Am Soc Mass Spectrom. 2009 Oct;20(10):1782-9. doi: 10.1016/j.jasms.2009.05.015. Epub 2009 Jun 6.
The presence of a peak centered near m/z 2862, observed for the first time for the caged dodecatungstate radical-anion, [W12O41]-, enables distinguishing WO2 from WO3 by Laser Desorption Ionization mass spectrometry (LDI-MS). In addition to WO2, laser irradiation of dry deposits made from aqueous ammonium paratungstate, and calcium and lead orthotungstate also produce the [W12O41]-. In contrast, spectra recorded from deposits made from aqueous Na2WO4, sodium metatungstate, and WO3, or non-aqueous calcium and lead orthotungstate, and ammonium paratungstate, failed to show the m/z 2862 peak cluster. These observations support the hypothesis that polycondensation reactions to form [W12O41]- occur solely in the presence of water. Although dry spots are irradiated for ionization, the solvent used for sample preparation plays an important role on the chemical composition endowed to ions detected. For example, the m/z 2862 peak seen from deposits made from aqueous ammonium paratungstate, and calcium and lead orthotungstate, is absent in the spectra recorded either from pristine deposits or those derived from solutions made with organic solvents such as acetonitrile or ethanol.
首次在笼状十二钨酸根自由基阴离子[W12O41]-*中观察到的、以质荷比2862为中心的峰的存在，使得通过激光解吸电离质谱法（LDI-MS）区分WO2和WO3成为可能。除了WO2，用仲钨酸铵水溶液以及正钨酸钙和正钨酸铅制备的干沉积物经激光照射后也会产生[W12O41]-。相比之下，用钨酸钠水溶液、偏钨酸钠以及WO3，或非水的正钨酸钙和正钨酸铅以及仲钨酸铵制备的沉积物记录的光谱，未能显示质荷比2862的峰簇。这些观察结果支持了这样一种假设，即形成[W12O41]-*的缩聚反应仅在有水的情况下发生。尽管为了电离对干斑进行了照射，但用于样品制备的溶剂对检测到的离子所具有的化学成分起着重要作用。例如，从仲钨酸铵水溶液以及正钨酸钙和正钨酸铅制备的沉积物中看到的质荷比2862的峰，在原始沉积物或由乙腈或乙醇等有机溶剂制成的溶液衍生的沉积物记录的光谱中并不存在。
