Non-aqueous capillary electrophoresis of drugs: properties and applicationof selected solvents

The electrophoretic mobility of selected acidic and basic test solutes have been determined in non-aqueous media prepared by adding various combinatio ns of ammonium acetate, sodium acetate, methane sulphonic acid and acetic a cid to acetonitrile, propylene carbonate, methanol, formamide, N-methylform amide, N,N-dimethylformamide and dimethylsulphoxide, respectively. The appa rent pH (pH*) of these non-aqueous media have been measured and it was foun d that pH* is an important factor for the separations in non-aqueous capill ary electrophoresis. However, in some solvents the concentration of sodium acetate has a strong influence on the mobility despite very small changes i n pH*. Due to the fact that a change in one parameter influences a number o f other parameters it is very difficult to conduct systematic studies in no n-aqueous media and to compare the migration of the species at fixed pH* va lues from one solvent to another. Thus pH* is only of value for comparison when used with a specific solvent or solvent mixture. The viscosity of the above-mentioned solvents were measured at various temperatures and means to adjust the viscosity of the non-aqueous media used for capillary electroph oresis are discussed and the separation of ibuprofen and its major metaboli tes in urine is used as an example. (C) 1999 Elsevier Science B.V. All righ ts reserved.