Resolution of isomers of sorbitolparaben esters by chromatographic and electrophoretic techniques.

Pharmaceutical preparations usually contain preservatives and sweeteners. When parabens are used as preservatives and a polyol as a sweetener, a transesterification reaction may happen, yielding the transester polyol-paraben. The products formed in the transesterification reaction of methylparaben and sorbitol were analyzed by micellar electrokinetic chromatography and by HPLC. Up to six positional isomers of sorbitolparaben (SPB) can be produced. However, only three peaks were found by HPLC. The higher efficiency and resolution power of MEKC allowed one to resolve five peaks. Results were compared with those obtained by capillary zone electrophoresis in borate buffer, where the separation of isomers occurred in a different way, because of a complexation between SPB and borate.