Department of Chemistry, University of Iowa, Iowa City, Iowa 52242-1294, United States.
Anal Chem. 2010 Nov 15;82(22):9289-98. doi: 10.1021/ac101797k. Epub 2010 Oct 28.
A novel application of single particle scanning transmission X-ray microscopy (STXM) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy is presented for quantitative analysis of hygroscopic properties and phase transitions of individual submicrometer particles. The approach utilizes the exposure of substrate-deposited individual particles to water vapor at different relative humidity followed by STXM/NEXAFS spectromicroscopy analysis. The hygroscopic properties of atmospherically relevant NaCl, NaBr, NaI, and NaNO(3) submicrometer particles were measured to evaluate the utility of the approach. An analytical approach for quantification of a water-to-solute ratio within an individual submicrometer particle during hydration and dehydration cycles is presented. The results for the deliquescence and efflorescence phase transitions and quantitative measurements of water-to-solute ratios are found in excellent agreement with available literature data. Oxygen K-edge NEXAFS spectra of submicrometer sodium halide droplets are reported along with a unique experimental observation of the formation of the halide-water anionic complex in NaBr and NaI microdimensional droplets. The analytical approach provides a unique opportunity for spectromicroscopy studies of water uptake on environmental particles collected in both laboratory and field studies.
本文提出了一种利用单颗粒扫描透射 X 射线显微镜（STXM）和近边 X 射线吸收精细结构（NEXAFS）光谱对单个亚微米颗粒的吸湿性和相变进行定量分析的新方法。该方法利用基底沉积的单个颗粒在不同相对湿度下暴露于水蒸气，然后进行 STXM/NEXAFS 光谱显微镜分析。测量了大气相关的 NaCl、NaBr、NaI 和 NaNO(3)亚微米颗粒的吸湿性，以评估该方法的实用性。提出了一种在单个亚微米颗粒的水合和脱水循环过程中定量计算水与溶质比的分析方法。在潮解和反潮解相变以及定量测量水与溶质比方面，得到的结果与现有文献数据非常吻合。报告了亚微米尺度的卤化钠液滴的氧 K 边 NEXAFS 谱，并观察到了在 NaBr 和 NaI 微尺度液滴中形成卤化物-水阴离子配合物的独特实验现象。该分析方法为在实验室和野外研究中收集的环境颗粒上水吸收的光谱显微镜研究提供了一个独特的机会。
