Differential spectrophotometric method for the determination of vitamin A (retinol) by using trifluoroacetic acid, and its application to related compounds

Abstract

A differential spectrophotometric procedure for the determination of vitamin A (retinol) based on the formation of a pink colour in a trifluoroacetic acid-perchloric acid medium has been developed. Maximum absorbance of the pink colour with λ_max. at 502 nm was attained within 7–12 min and remained stable for at least 30 s; the intensity of this colour was equivalent to 45 per cent. of the intensity of the blue colour produced by the well known antimony(III) chloride procedure. The pink colour could be destroyed within 2–4 min by the addition of pentane-2,4-dione followed by hydrogen peroxide. A rectilinear graph of absorbance versus amount of vitamin A was obtained for the 0–20-µg range, optimum results being achieved in the 5–10-µg range. The relative standard deviation of the method for 8·3 µg was ±0·7 per cent. The reactions of vitamin A acetate, retinal, retinoic acid, β-carotene, ergocalciferol, cholecalciferol, cholesterol, ergosterol, phytonadione and α-tocopherol were also investigated employing the same reagent additions.