Solvent microextraction with simultaneous back extraction and the effect of tetra-n-butylammonium ion on ODS bonded phase.

摘要

This thesis is in two parts. In Part I, a solvent microextraction technique is developed to perform simultaneous forward- and back-extraction across a microliter size organic liquid membrane. The organic liquid membrane phase, consisting of 30--80 muL of n-octane, is layered over 0.5--1.6 mL of stirred aqueous sample solution in a 1- or 2-mL micro-reaction vial, which is buffered at high pH for the extraction of basic drugs. The membrane phase is stabilized against mechanical disruption by a small Teflon ring, even when the sample solution is stirred at a speed of 2000 rpm. Two different versions of the apparatus are employed; one for quantitative extraction and the other for high preconcentration. For achieving quantitative extraction, the receiving phase is a 100- or 200-muL aqueous phase buffered at low pH, which is layered over the organic membrane phase. After extraction for a prescribed time, an aliquot of the receiving phase is injected directly into an HPLC for quantification. In 30 min, the basic drugs, mephentermine and 2-phenylethylamine, in a 0.5 or 1.0 mL of pH 13 aqueous sample solution are 100% and 90% extracted, respectively, into a 100 or 200 muL of pH 2.1 aqueous receiving phase. For achieving high preconcentration, the receiving phase is a 1.0- or 0.50-muL microdrop of a pH 2.1 aqueous phase, which is suspended in the organic membrane phase directly from the tip of a microsyringe needle. The source phase is a 1.6-mL sample solution buffered at pH 13. After extraction for a prescribed time, the complete microdrop is injected into an HPLC for quantification. In 15 min, the enrichment factors in the 1.0-muL receiving phase are about 500 for methamphetamine, mephentermine and methoxyphenamine, and about 160 for 2-phenylethylamine. Enrichment factors are approximately doubled for the same 15-min extraction time by using a 0.50-muL receiving drop. A quantitative kinetic model, based on the Whitman two-film theory, is been developed to describe the extraction process and is been verified experimentally.;In Part II of this thesis, the simultaneous sorption of tetra- n-butylammonium ion (TBA+) and butanol on the bonded phase sorbent Partisil-10-ODS-3 from water (the mobile phase), at two different ionic strengths 0.50 and 0.050 mol/L, is studied by the column equilibration technique. When the TBA+ concentration in the mobile phase is kept constant at 1 x 10-4 mol/L while the butanol concentration is varied from 0 to 0.03 mol/L, the plots of moles of TBA + sorbed versus moles of butanol sorbed from mobile phases decrease linearly for both ionic strengths. This indicates that butanol simply competes with TBA+ for sorption space. In contrast, when the butanol concentration in the mobile phase is kept constant at 1 x 10 -3 mol/L while the TBA+ concentration is varied from 0 to 0.050 and 0.50 mol/L for the ionic strengths 0.050 and 0.50 mol/L, respectively, the plots of moles of butanol sorbed versus moles of TBA + sorbed from mobile phases decrease, but not linearly. This indicates that, in addition to competing with butanol for space, sorbed TBA+ also has a second effect. The second effect of sorbed TBA + is that it causes an unfolding of the originally collapsed ODS chains. The unfolding of the ODS chains causes an increase in sorption space for butanol, a decrease in overlap between sorbed TBA+ and butanol, and a decrease in the distribution coefficient of butanol. The last effect is due to reduced contact area between sorbed butanol and ODS chains. A quantitative model, developed on the basis of the above assumptions, fits well to the experimental data.