Microabsorptiometry of Chemically-Induced Single Picoliter Droplet/Water Extraction

我们已经开发了一种新的微吸收技术结合微毛细管操作和微电极方法，通过该技术可以将单个皮升微滴或微粒注入水溶液中，并测量从水到单个液滴（溶剂萃取）或颗粒（固相萃取）的溶质萃取。在油滴/水体系中，亚甲基蓝（MB）或（二茂铁甲基）三甲基铵（Fc）与PF_6^-的离子对萃取速度非常快，与溶质在水中的扩散限制速率相当。另一方面，MB和十二烷基硫酸根阴离子（SDS）之间的离子对萃取是非常缓慢的，并在连续反应模型的基础上分析了萃取的时间依赖性。此外，速率常数高度依赖于液滴尺寸。结果表明，萃取是由SDS和/或SDS-MB离子对吸附在液滴/水界面。在微粒/水体系中，研究了阳离子染料在单一硅胶微粒中的吸附和脱附过程。若丹明6 G的吸附/脱附过程的速率控制步骤是染料在微粒中的扩散，而MB或吖啶橙子的传质过程则是染料在固/水界面上的扩散和脱附。得出的结论是，单个微滴或微粒的微毛细管注射/操作、微吸收测量和微电化学技术足以定量分析提取过程。由于萃取率取决于液滴或颗粒尺寸，因此目前的测量对于萃取过程的详细分析绝对重要。

We have developed a new microabsorption technique combined with microcapillary manipulation and microelectrode methods, by which a single picoliter microdroplet or microparticle can be injected into an aqueous solution and extraction of a solute from water to the single droplet (solvent extraction) or particle (solid phase extraction) is measured. In the oil droplet/water system, ion-pair extraction between methylene blue (MB) or (ferrocenylmethyl)trimethylammonium (Fc) and PF_6^- was so fast, comparable with the diffusion-limited rate of the solute in water. On the other hand, ion-pair extraction between MB and a dodecylsulfate anion (SDS) was very slow and the time dependence of the extraction was analyzed on the basis of a consecutive reaction model. Furthermore, the rate constants were highly dependent on the droplet size. The results indicate that the extraction is governed by adsorption of SDS and/or the SDS-MB ion-pair at the droplet/water interface. In the microparticel/water system, sorption and desorption processes of a cationic dye in single silica gel particle were kinetically analyzed. A rate-determining step of the sorption/desorption processes of rhodamine 6G was the diffusion of the dye in the microparticle, while the mass transfer processes of MB or acridine orange were expected to be governed by the intraparticel diffusion and desorption of the dye on the solid/water interface. It is concluded that microcapillary injection/manipulation, microabsorptiometry and microelectrochemistry techniques of a single microdroplet or microparticle is sufficient to quantitatively analyze the extraction processes. Since the extraction rate depends on the droplet or particle size, the present measurements are absolutely important for the detailed analysis of the extraction processes.