The identification and semi-quantitative assay of some fat-soluble vitamins and antioxidants in pharmaceutical products and animal feeds by thin-layer chromatography

ANALYSTANALYST Pub Date: DOI: 10.1039/AN9739800257

Abstract

A thin-layer chromatographic method for the identification and semi-quantitative assay of vitamin A (alcohol), its acetate and palmitate, vitamin D, α-tocopherol, α-tocopheryl acetate, BHA (butylated hydroxyanisole; 2-t-butyl-4-methoxyphenol), BHT (butylated hydroxytoluene; 2,6-di-t-butyl-4-methyl-phenol) and ethoxyquin in vitamin preparations is described. The sample solutions are applied to thin layers of silica gel and the vitamins and antioxidants are separated by using n-hexane-ethyl methyl ketone-di-n-butyl ether (34 + 7 + 6) as the developing solvent. Decomposition of vitamins A and D when applied to the adsorbent layer is inhibited by the presence of triethylamine in the spotting solvent. The compounds are identified by means of their RF values, their appearance in ultraviolet radiation of wavelengths 254 and 360 nm and their response to iron(III) chloride-bipyridyl and iron(III) chloride-potassium hexacyanoferrate(III) spray reagents; they are assayed by visual comparison with standards. The method has been applied to gelatin-protected vitamin beads, animal feed additives, multivitamin tablets, oily vitamin concentrates and halibut-liver oil samples.

A simple colour test for distinguishing vitamin D2 from vitamin D3 after removal of vitamin A and its esters is also described.

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