Study of chemistry in droplets with net charge before and after Coulomb explosion: Ion-induced nucleation in solution and implications for ion production in an electrospray
Study of chemistry in droplets with net charge before and after Coulomb explosion: Ion-induced nucleation in solution and implications for ion production in an electrospray
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DOI：
10.1021/ac048536g
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发表时间：
2005-05-15
影响因子：
7.4
通讯作者：
Agnes, GR
中科院分区：
文献类型：
--
作者：
Bakhoum, SFW;Agnes, GR
带净电荷的液滴是电喷雾离子源产生气态离子的重要中间体。关于这种液滴由于违反电中性而发生的化学反应，可能有大量的知识。这样的信息可以导致离子产生过程中的ES沿着的因素，影响it. The进行的实验涉及悬浮的单独带电液滴，并没有，允许进行库仑爆炸，而他们仍然悬浮在电动平衡（EDB）。通过检查悬浮液滴内形成的沉淀物，观察到NaCl沉淀的开始在质量与净电荷（m/z）比< -4.8 X 10（9）amu/e的液滴（甘油：水9：lv/v）中得到促进。基本上在ES中产生的所有液滴中都超过了该阈值m/z值，因为它高于库仑爆炸的计算阈值。这一发现表明，具有净电荷的液滴中的簇形成可以发生在溶质浓度低于均匀成核的基础上所预期的。研究了液滴中存在的沉淀物等大颗粒对液滴库仑爆炸动力学的影响。使用初始尺寸和净电荷大小在实验误差范围内相等但溶质浓度不同的液滴，我们发现库仑爆炸后其主要残留物的m/z不同。与由具有较低初始珠浓度（21 nM）的起始溶液产生的主要残留物相比，对于起始溶液中较高的初始珠浓度（320 nM），经历库仑爆炸的含有20 nm荧光珠的微米大小的液滴产生具有较高m/z的主要残留物。
Droplets with net charge are essential intermediaries in the production of gaseous ions in the electrospray (ES) ion source. There could be a wealth of knowledge regarding the chemistry that occurs in such droplets as a result of their violation of electroneutrality. Such information could lead to improved understanding of the ion generation process in an ES along with factors that affect it. The experiments performed involved the levitation of individually charged droplets that were, and were not, allowed to undergo Coulomb explosion while they remained levitated in an electrodynamic balance (EDB). Through examination of precipitates formed within the levitated droplets, it was observed that onset of NaCl precipitation was promoted in droplets (glycerol:water 9:1 v/v) that had mass-to-net-charge (m/z) ratio < -4.8 x 10(9) amu/e. This threshold m/z value is exceeded in essentially all droplets generated in an ES because it is above the calculated threshold for Coulomb explosion. This finding suggests that cluster formation in droplets having net charge could occur at solute concentrations lower than would be anticipated on the basis of homogeneous nucleation. The effect of large entities such as precipitates existing in the droplet on the dynamics of droplet Coulomb explosion was also examined. Using droplets whose initial size and magnitude of net charge were equivalent within experimental error but having different concentration of solutes, we showed that the m/z of their main residues following Coulomb explosion were different. Micrometer-size droplets containing 20 nm fluorescent beads that underwent Coulomb explosion resulted in main residues that had higher m/z for higher initial bead concentration in the starting solution (320 nM) when compared to main residues resultant from starting solutions having lower initial bead concentration (21 nM).