Behavior and Use of Nonaqueous Media without Supporting Electrolyte in Capillary Electrophoresis and Capillary Electrochromatography

Abstract

Five nonaqueous solvents (acetonitrile, methanol, N,N-dimethylformamide, dimethyl sulfoxide, formamide) and deionized water were investigated for their ability to support electroosmotic flow (EOF) without electrolytic additives. In general, flow was found to be equal to or greater than flow with typical CE buffer systems. The magnitude of EOF was determined for each solvent by open tubular capillary electrophoresis (CE) and related to viscosity (eta), dielectric constant (epsilon), and the ratio of dielectric constant to viscosity (eta/epsilon). Zeta potentials (zeta) were derived indirectly from flow data and tabulated. Comparisons of flow behavior and zeta were made between pure solvents and conventional CE buffers, and questions of equilibrium and reproducibility were addressed. Similar experiments were performed using hydroorganic mobile phases (ACN/water, MeOH/water) across the complete compositional range (100% water-100% organic), with flow characteristics and zeta reported for each mobile phase system. Packed capillary columns (5-microns ODS) were evaluated for flow and retention stability under capillary electrochromatographic (CEC) conditions. A separation of 11 polycyclic aromatic hydrocarbons was performed in under 13 min by CEC with an ACN/water mobile phase. Reduced plate heights (h) were calculated between 2.5 and 3.0 for solutes with capacity factors (k') up to 4.5 for the most retained solute.

Separation of related opiate compounds using capillary electrochromatography

“…These results can be attributed to a decrease in viscosity and dielectric constant with an increase of volume percent of acetonitrile. Also, the same trend was shown to occur with inorganic buffers [42]. For CEC, the effect of the organic modifier is rather different than for CZE.…”

Molecularly imprinted polymer films grafted from porous or nonporous silica: Novel affinity stationary phases in capillary electrochromatography

“…The increase in EOF at higher acetonitrile contents is in agreement with other reports. Wright et al [22] explained this trend by estimating the ratio e r /Z and the z values of solutions composed of H 2 O and acetonitrile, and it was possible to both observe that minima values of e r /Z were obtained at intermediate percentages of organic modifier and that z was increasing by increasing the acetonitrile content. Although the parameters governing the binary system composed of water and acetonitrile are different from those of a buffer-acetonitrile system, these studies can justify the behavior here described.…”

Sensitive capillary electrophoresis microchip determination of trinitroaromatic explosives in nonaqueous electrolyte following solid phase extraction

“…To date, there has been only one reported example of a pure nonaqueous phase separation performed on a microchip platform [19], although several have utilized solvent programming of organic/aqueous buffers [14,20]. Pure acetonitrile was shown by Wright et al to have an electroosmotic mobility in CE that is more than three times that of a pH 9 borate buffer [21]. This attribute can lead to substantially faster separation times on a microchip.…”