Microabsorptiometry of Chemically-Induced Single Picoliter Droplet/Water Extraction

我们发展了一种新的微吸收技术，结合微毛细管操纵和微电极方法，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或微粒的萃取(溶剂萃取)或颗粒(固相萃取)。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~-之间的离子对萃取速度非常快，相当于溶质在水中的扩散限制速率。另一方面，MB与十二烷基硫酸盐阴离子(SDS)之间的离子对萃取非常缓慢，并根据连续反应模型分析了萃取的时间依赖性。此外，速率常数高度依赖于液滴的大小。结果表明，萃取剂在水滴/水界面上的吸附是由十二烷基硫酸钠和(或)十二烷基硫酸钠-甲基溴化铵离子对的吸附控制的。在微粒/水体系中，对阳离子染料在单一硅胶微粒中的吸附和解吸过程进行了动力学分析。罗丹明6G的吸附/脱附过程的一个速率决定步骤是染料在微粒中的扩散，而MB或丫啶橙的传质过程预计是由染料在固/水界面上的微粒内扩散和脱附控制的。结果表明，单个微滴或微粒的微毛细管注射/操纵、微吸光光度和微电化学技术足以定量分析萃取过程。由于萃取率取决于液滴或颗粒大小，因此目前的测量对于详细分析萃取过程是绝对重要的。

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.