Water microdroplets promote unusual chemical reactions at the air–water interface. However, the interfacial structure of water microdroplets and its potential influence on chemical processes are still enigmatic. Here, we present evidence of in-droplet fractionation of water isotopologues. Employing a sonic spray, we atomized the heavy water (D₂O, 99.9 atom % D) solution of three classes of organic compounds (basic, acidic, and neutral). The analytes were predominantly desorbed from the resulting droplet surface in protonated form rather than deuterated form, as detected by mass spectrometry. This result remained unaltered upon adding formic acid-d₂ (DCOOD) to the droplet. Monitoring Dakin oxidation of benzaldehyde at the surface of binary microdroplets composed of 1:1 (v/v) D₂O/H₂¹⁸O revealed the preferred formation of phenolate-¹⁶O over phenolate-¹⁸O. Atmospheric pressure chemical ionization mass spectrometric analysis of the vapor composition in the sprayed aerosol revealed the preferential evaporation of lighter water isotopologue impurities from the surface of heavy water microdroplets. These results indicate the enrichment of lighter water isotopologue impurities (HOD/H₂O) on the surface of heavy water microdroplets, implying possible future developments for water isotopologue fractionation using microdroplets.

中文翻译：

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重水微滴表面富集较轻的同位素杂质


水微滴促进空气-水界面上不寻常的化学反应。然而，水微滴的界面结构及其对化学过程的潜在影响仍然是个谜。在这里，我们提出了水同位素体的液滴内分馏的证据。采用声波喷雾，我们雾化了三类有机化合物（碱性、酸性和中性）的重水（D ₂ O，99.9 原子% D）溶液。通过质谱检测，分析物主要以质子化形式而不是氘化形式从所得液滴表面解吸。向液滴中添加甲酸-d ₂ (DCOOD) 后，该结果保持不变。监测由 1:1 (v/v) D ₂ O/H ₂ ¹⁸ O 组成的二元微滴表面苯甲醛的 Dakin 氧化揭示了首选酚盐- ¹⁶ O 的形成超过酚盐- ¹⁸ O。对喷雾气溶胶中蒸气成分的大气压化学电离质谱分析表明，较轻的水同位素异体杂质优先蒸发。重水微滴表面。这些结果表明轻水同位素体杂质（HOD/H ₂ O）在重水微滴表面富集，这意味着使用微滴进行水同位素体分馏的未来可能发展。