SEPARATION OF 13-CIS AND ALL-TRANS-RETINOIC ACID AND THEIR PHOTODEGRADATION PRODUCTS USING CAPILLARY ZONE ELECTROPHORESIS AND MICELLAR ELECTROKINETIC CHROMATOGRAPHY (MEC)

Two retinoic acid isomers; 13-cis retinoic acid and all-trans retinoic acid and their photodegradation productS were resolved with capillary electrophoresis (CE) (UV detector, 345 nm) using three different mobi le phases: method 1 - an acetonitrile modified borate buffer (pH 8.5); method 2 - borate buffer (pH 8.5) modified with acetonitrile and alph a-cyclodextrin; and method 3 - borate buffer (pH 8.5) modified with SD S (MEC). Concentration of acetonitrile in the buffer was varied from 1 0 to 50% in method 1 and resolutions of 0-1.9 were obtained for the tw o retinoic acid isomers. Similarly in method 2, concentration of alpha -cyclodextrin in the buffer (with 10% acetonitrile) was varied from 0 to 40 mM, giving resolutions of 0-3.8. In method 3, concentration of S DS in the buffer was varied from 5 to 60 mM resulting in resolutions o f 1.3-4.1. Optimum separation conditions for the three methods were ap plied to the separation of photodegradation products of the two retino ids after exposure to fluorescent light for 36 h. A buffer modified wi th 45% acetonitrile and the same buffer modified with 10 mM SDS gave i ncompletely resolved electropherograms with a 72 cm x 50 mum capillary (50 cm to the detector). A buffer containing 20 mM alpha-cyclodextrin 10% acetonitrile gave completely resolved peaks for each isomer. The buffer containing 10 mM SDS gave completely resolved peaks for the pho todegradation products when a 122 cm x 50 mum capillary (100 cm to det ector) was used.