Nonaqueous Capillary Electrophoresis

Only a few attempts to perform nonaqueous paper electrophoresis have been described and these articles

Haswell SJ (1997) Developments and operating characteristics of microflow injection analysis systems based on electroosmotic flow. Analyst 122: 1R-1OR.

Manz A and Becker H (1997) Microsystem Technology in Chemical and Life Sciences. Berlin: Springer.

Madou M (1996) Fundamentals of Microfabrication. Boca Raton: CRC.

Martin AJP (1962) Opening lecture. In: Van Swaay M (ed.) Fourth International Symposium on Gas Chromatography. London: Butterworths.

Oefner PJ, Bonn GK and Chiesa C (1995) Encyclopaedia of Analytical Chemistry, pp. 1041-1152. London: Academic Press.

Pethig R and Markx GH (1997) Applications of dielec-trophoresis in biotechnology, Trends in Biochemistry 15: 426-432.

Regnier F (1999) The evolution of analysis in life science research and molecular medicine: the potential role for separations. Chromatographia 49: S56-S64.

Tsuda T (ed.) (1995) Electric Field Applications, pp. 47-73. Weinheim: VCH.

were reviewed in 1978. In 1984 nonaqueous capillary electrophoresis (NACE) was briefly mentioned in a single publication, but not utilized further. However, since 1993 the use of nonaqueous media for capillary electrophoresis has seen renewed interest in the separation of drug substances due to the high separation selectivity obtained in these systems.

The electrophoretic migration of the solutes is in-Suenced by the nature of the solvent or solvent mixture used for the electrophoresis medium in three main ways:

1. The mobility may change due to changes in the size of the solvated ion.

2. The dielectric constant of the organic solvent may inSuence the equilibrium of the protolytic dissociation. The higher the value of the dielectric constant, the higher the degree of ionization of acids and bases.

3. The acid-base property of the solute, expressed by its pKa value, may change due to the differentiating effect of many organic solvents.

The latter effect of the three is the most significant, as the dissociation constant, Ka, may change many orders of magnitude for different solvents.

The increased selectivity of separation in organic solvents compared to aqueous systems is due to the fact that the levelling effect of water is eliminated. If

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