Separation of 13- cis and all- trans retinoic acid and their photodegradation products using capillary zone electrophoresis and micellar electrokinetic chromatography (MEC)

Abstract

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 mobile phases: method 1— an acetonitrile modified borate buffer (pH 8.5); method 2 — borate buffer (pH 8.5) modified with acetonitrile and α-cyclodextrin; and method 3 — borate buffer (pH 8.5) modified with SDS (MEC). Concentration of acetonitrile in the buffer was varied from 10 to 50% in method 1 and resolutions of 0–1.9 were obtained for the two retinoic acid isomers. Similarly in method 2, concentration of α-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 SDS in the buffer was varied from 5 to 60 mM resulting in resolutions of 1.3–4.1. Optimum separation conditions for the three methods were applied to the separation of photodegradation products of the two retinoids after exposure to fluorescent light for 36 h. A buffer modified with 45% acetonitrile and the same buffer modified with 10 mM SDS gave incompletely resolved electropherograms with a 72 cm × 50 μm capillary (50 cm to the detector). A buffer containing 20 mM α-cyclodextrin 10% acetonitrile gave completely resolved peaks for each isomer. The buffer containing 10 mM SDS gave completely resolved peaks for the photodegradation products when a 122 cm × 50 μm capillary (100 cm to detector) was used.