Drug purity determination by capillary electrophoresis : Practical and theoretical aspects on peak shape and resolution

Sammanfattning: Capillary electrophoresis was used for separation and determination ofdrugs. Structural analogues, enantiomers and rotamers were separated usingderivatized β-cyclodextrins and γ-cyclodextrins as selectors.In order to improve these separation systems different kinds of chargedamphiphiles were introduced in the background electrolyte (BGE).Addition of charged amphiphiles to the BGE reduces the adsorption ofdrugs with the same charge as the amphiphile and it will also alter theelectroosmotic flow (EOF). Regulation of the EOF was used to improve theresolution as well as for decreasing the time of analysis. A new theory wasdeveloped where the magnitude of the EOF is described as a function of theamphiphile concentration in the BGE. A good correlation between thetheoretical calculated values and the experimental data was obtained.Methods for control of the overloading effects in drug puritydeterminations are also presented. Regulation of the peak shape of anoverloaded peak and for minimization of the electromigration dispersion ofthe sample zone were accomplished by addition of tetraalkylammoniumions to the BGE having a mobility similar to the mobility of the sample ions.Presence of selectors such as cyclodextrins enables tuning of the conductivityof the sample zone. This technique was successfully applied for separationenantiomers and in determination of enantiomeric drug purity. Laserinduced fluorescence detection, promote minimization of the overloadingeffects by injection of a lower sample concentration.A He-Cd laser and a frequency doubled argon-ion laser were applied asexcitation sources in drug purity determinations. The high detectability offluorescent compounds using LIF-detection improved the limit ofdetermination of impurities.