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Abstract
Vitamin A compounds, both natural and synthetic (collectively called retinoids), are important in the maintenance of the integrity of epithelial structures. The metabolism of natural retinoids such as retinol, retinal, retinoic acid, and retinyl esters has been studied extensively, and the metabolites have been determined by several techniques. The analytical techniques that were commonly used in the past were column chromatography, thin-layer chromatography (TLC), and gas liquid chromatography. However, the high-performance liquid chromatographic (HPLC) technique has proven to be by far the method of choice for the determination of retinoids. The determination of natural retinoids is facilitated by their inherent chemical properties, such as their intense absorption in the near ultraviolet (UV) region and the ability of several retinoids to fluoresce. These properties are often advantageous, particularly in the on-line determination of these compounds; an example is by UV in the HPLC technique. Since retinoids are unstable in the presence of light and air, special precautions must be taken in their extraction from and determination in biological materials.
