RATIONALE In droplet-assisted ionization (DAI), intact molecular ions are generated from molecules in aerosol droplets by passing the droplets through a temperature-controlled capillary inlet. Ion formation is explored through the effects of analyte mass flow, droplet solvent composition, and capillary temperature on ion signal intensity. METHODS A Waters SYNAPT G2-S is adapted for DAI by reconfiguring the inlet with a temperature-controlled capillary. Droplets are generated by atomization of a solution containing analyte and then sampled through the inlet. If desired, solvent can be removed from the droplets prior to analysis by sending the aerosol through a series of diffusion dryers. Size distributions of the dried aerosols allow the mass flow of analyte into the inlet to be determined. RESULTS Analyte signal intensities are orders of magnitude higher from droplets containing a protic solvent (water) than an aprotic solvent (acetonitrile). The highest signal intensities for DAI are obtained with inlet temperatures above 500°C, though the optimum temperature is analyte dependent. At elevated temperatures, droplets are thought to undergo rapid solvent evaporation and bursting to produce ions. The lowest signal intensities are generally obtained in the 100-350°C range, where slow solvent evaporation is thought to inhibit ion formation. As the temperature decreases from 100°C down to 25°C, the signal intensity increases significantly. When 3-nitrobenzonitrile, a common matrix for solid-state matrix-assisted ionization (MAI), is added to droplets consisting of 50/50 v/v water and acetonitrile, the matrix enhances ion formation to produce a signal intensity comparable to DAI in 100% water. CONCLUSIONS The results are consistent with other inlet ionization techniques, suggesting that similar ion formation mechanisms are operative. Optimized ion yields (the combined effects of ionization probability and ion transmission) for DAI are currently in the 10-5 to 10-6 range, which is sufficient for many aerosol applications.

中文翻译：

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液滴辅助电离中的离子形成。

理由在液滴辅助电离（DAI）中，通过使液滴穿过温度可控的毛细管入口，从气溶胶液滴中的分子产生完整的分子离子。通过分析物质量流量，液滴溶剂组成和毛细管温度对离子信号强度的影响来探索离子的形成。方法Waters SYNAPT G2-S通过用温度控制的毛细管重新配置进样口而适用于DAI。液滴是通过雾化包含分析物的溶液生成的，然后通过入口进行采样。如果需要，可以在分析之前通过将气雾剂通过一系列扩散干燥器从液滴中除去溶剂。干燥气溶胶的尺寸分布可以确定待分析物进入入口的质量流量。结果含有质子溶剂（水）的液滴的分析物信号强度要比非质子溶剂（乙腈）高几个数量级。DAI的最高信号强度是在入口温度高于500°C时获得的，尽管最佳温度取决于分析物。在高温下，液滴被认为会经历快速的溶剂蒸发并破裂而产生离子。最低的信号强度通常在100-350°C的范围内获得，认为缓慢的溶剂蒸发会抑制离子的形成。当温度从100°C降至25°C时，信号强度显着增加。当将3-硝基苄腈（一种用于固态基质辅助电离（MAI）的通用基质）添加到由50/50 v / v水和乙腈组成的液滴中时，基质增强离子形成，从而产生与100％水中的DAI相当的信号强度。结论该结果与其他入口电离技术一致，表明类似的离子形成机理是可行的。DAI的最佳离子收率（电离几率和离子传输的综合作用）目前在10-5至10-6的范围内，足以用于许多气雾剂应用。