Spectrophotometric Study of a New Colorimetric Reaction of Vitamin A* by Albert E. Sobel

This paper deals with a new calorimetric reaction of vitamin A with glycerol 1,3-dichlorohydrin (which we henceforth will refer to as GDH) that appears to be suitable for the quantitative estimation of this vitamin. The estimation of vitamin A in vitro has been the subject of many reviews in recent years (l-6). The two widely used methods at present are the ultraviolet absorption at 325 to 328 rnp, and the determination of the maximum absorption at 615 to 620 rnp of the blue color formed on the addition of a solution of antimony trichloride in chloroform to the vitamin in the same solvent (Carr-Price reaction). One disadvantage of the ultraviolet method is that there are substances in natural products other than vitamin A which absorb at around 328 mp (7). Another drawbhck of the method is the need for expensive equipment. The Carr-Price reaction does not, require expensive equipment and is more specific for vitamin A (8). Its disadvantages are the rapidity with which the maximum absorption must be read, owing to the fading of the color, and the instability of the reagent. The new calorimetric reaction reported herein possesses the same advantages that the Carr-Price reaction has over the ultraviolet absorption method, and in addition possesses the following advantages over the CarrPrice reaction. (1) The stability of the color produced permits its measurement with ease any time from 2 to 10 minutes after the reagents are mixed. (We have even been able to measure the color in a visual colorimeter.) (2) The reagent employed is stable. It is not affected by traces of moisture and leaves no film which might interfere in the absorption of the colored solution. The disadvantage of the new reaction is that the extinction coefficient! (L:?$,,, X 550 mp) of the color produced is about onefourth that of the antimony trichloride blue color (Li7&., X 615 m/l).