Effects of organic solvents on sample pretreatment and separation performances in capillary electrophoresis

Abstract

A review of recent developments in theoretical as well as application studies concerning the use of organic solvents, either as purely nonaqueous solvents, hydro-organic mixtures, or a combination of an organic solvent with another organic modifier(s), in the sample matrix and/or separation buffer for effecting sample pretreatment and/or improving separation performances in capillary electrophoresis (CE) is presented. In particular, recent advances made in furthering the basic understanding of selectivity changes that occur in capillary zone electrophoresis due the presence of organic solvents in the separation medium, based on in-depth studies of fundamental processes, such as acid-base chemistry, ion-ion and ion-solvent interactions, were discussed in detail. The utilization of organic solvents for improving the resolution of highly challenging and important separations, i.e., those involving the separation of positional and optical isomers, was also critically reviewed. Furthermore, a comprehensive survey of the use of organic solvents for on-line sample pretreatment, e.g., minimizing aggregation and maximizing solubilization of hydrophobic analytes, improving concentration detection sensitivity for analytes via the use of sample stacking, was presented and discussed. Moreover, recent applications involving the use of organic solvents for improving the CE separations of a variety of molecular species with significance in various disciplines, including biological, environmental and pharmaceutical areas, were summarized and tabulated.

Investigation of solvent effects in capillary electrophoresis for the separation of biological porphyrin methyl esters

“…The profile of these electrophoretic mobility versus methanol-ACN mixture curves for the various charged porphyrin methyl esters (Fig. 6) can be explained in part by a change in the viscosity of the separation medium as the percentage of methanol content was increased [38,40]. Also, these observed changes in the electrophoretic mobility can be attributed to an overall increase in the basicity of the mixed organic system [38,40], as well as to a slight variation in the overall dielectric constant, which may lead to changes in resolution due to its effect on ion-pair formation [38] and the magnitude of the EOF [21,22].…”

“…Compared to ACN, methanol possesses different physicochemical properties, such as relatively strong hydrogen donor/ acceptor strength and slightly lower dielectric constant. Thus, the addition of methanol into ACN could alter the electrophoretic mobilities of these positively charged porphyrin esters by changing, for examples, their solvation and acid-base properties [21,22,38,39].…”

Influence of methanol on the enantioresolution of antihistamines with carboxymethyl‐β‐cyclodextrin in capillary electrophoresis

“…Wren and Rowe [9,10] have described the role of organic solvents on chiral separations in CE. They used a simple mathematical model that accounts for the effect of a neutral chiral selector on the enantioseparation of basic analytes [9,[11][12][13][14].…”

“…They used a simple mathematical model that accounts for the effect of a neutral chiral selector on the enantioseparation of basic analytes [9,[11][12][13][14]. According to their model the addition of an organic modifier in the running buffer can lead to an increase or a decrease in separation depending upon whether the chiral selector concentration is above or below the optimal value for the solvent-free system [9,10]. In addition, it is also recognized that organic modifiers can have an effect on the electroosmotic flow (EOF), the viscosity, the dielectric constant, the conductivity of the BGE, and the solubility of analytes and CDs [4,15,16].…”

Separation of fluorescein isothiocyanate‐labeled amines by microchip electrophoresis in uncoated and polyvinyl alcohol‐coated glass chips using water and dimethyl sulfoxide as solvents of background electrolyte

“…The use of organic solvents as separation media in CE has gained increasing interest during the last few years [18][19][20][21][22][23]. The interest has been nourished by the possibility of altering the separation parameters, such as resolution, analysis time, and selectivity, simply by modifying the composition of the background electrolyte (BGE) [24][25][26][27][28].…”