Almost all separations with capillary electrophoresis (CE) have been carried out in the aqueous or aqueous-organic media. Reports of analysis in nonaqueous media are rare....[ Read more ]

Almost all separations with capillary electrophoresis (CE) have been carried out in the aqueous or aqueous-organic media. Reports of analysis in nonaqueous media are rare.

Separations of several types of basic drugs were examined by using nonaqueous capillary zone electrophoresis (NA-CZE). The separations were performed in a running medium consisting of 49% acetonitrile, 50% methanol, 1% acetic acid and 2OmM ammonium acetate. Using this medium, complete separation of mixtures of nine morphine substitutes, eleven antihistamines, eleven antipsychotics, ten stimulants and six antidepressants could in each case be achieved within a seven-minute run. Complete separation of 3 1 basic drugs could also be attained in less than 15 minutes. With the careful choice of the type of electrolyte and its concentration, baseline separation of mixtures of six morphine substitutes and six antihistamines could both be achieved in less than 2.5 minutes. Precision data on migration time and normalized peak area (peak area/migration time) were obtained from the above separations. The results showed that the use of liquid-cooled CE system with better solvent evaporation control would provide an excellent repeatability on both the migration time and normalized peak area (around 1% R.S.D. with the use of an internal standard). In an ambient air-cooled CE system with poor solvent evaporation control, non-volatile electrolyte gave better precision data than volatile one. Unusual selectivity was observed in the nonaqueous media. Both the change in the composition of organic solvents and the type of electrolyte could alter the selectivity of analytes.

In addition, aromatic acids could be separated by the above nonaqueous medium. With only minor modifications to this running medium, environmental pollutants with aniline groups could also be completely separated. Our system was capable of differentiating positional isomers of aromatic acids and environmental pollutants.

The purpose of the development of NA-CZE is to explore a new area for the analysis of highly hydrophobic compounds in CE. With the addition of chlorobenzene to our nonaqueous running medium, highly hydrophobic fullerene derivatives with ionizable functional group could be resolved by NA-CZE. Besides chargeable compounds, neutral compounds such as C₆₀ and C₇₀ could also be separated by using a commercially available GC column with γ-cyclodextrin-bonded stationary phase.

Our results clearly showed that nonaqueous CE is a powerful and new separation mode of CE that brings speed, reproducibility, simplicity, selectivity, wide applicability to the inherently efficient method of electrophoresis. Nonaqueous CE has established itself as an important and widely utilized technique for routine analytical separations.