The estimation of serum vitamin A with activated glycerol dichlorohydrin.

This paper deals with a new method for the estimation of vitamin A in blood serum based on the new calorimetric reaction between vitamin A and activated glycerol dichlorohydrin (GDH) . Most of the available methods for estimating vitamin A in blood serum depend upon the antimony trichloride reaction (l-6). The drawbacks to this reaction are that (1) the color is unstable and must be read within 5 seconds after addition of the reagent (unless low temperature is employed) ; (2) it is sensitive to moisture in air and reagents, and thus extreme anhydrous precautions must be observed; and (3) the reagent is corrosive and is a source of danger to the instruments employed. During the course of our investigations Bessey et ul. (7) reported a method for the determination of vitamin A in small quantities of serum which is dependent on the measurement of the ultraviolet absorption of serum extracts at 328 rnp before and after irradiation with ultraviolet light. These determinations require expensive equipment, including an ultraviolet spectrophotometer and an ultraviolet lamp for irradiation. Hemolyzed blood has been found to give higher carotene values, and due to the high blanks after irradiation, the results tend to be unreliable (see Table I). Recently a new calorimetric reaction of vitamin A was reported, which takes place on the addition of practical (8) or activated (9) glycerol dichlorohydrin to a solution of vitamin -4 in chloroform. This new reaction appears to be suitable for quantitative purposes, since it obeys Beer’s law over a reasonable range, and offers the following advantages over the widely used Carr-Price reaction (1) : (1) the violet color produced is stable for from 2 to 10 minutes after the addition of the reagent, (2) the reagent is not affected by traces of moisture on the most humid days, (3) no film of antimony oxychloride is left on the cuvettes, (4) the reagent is practically non-corrosive, and (5) the stable color makes possible the use of a slow reading, null-point spectrophotometer (Beckman) in the measurement of the absorption of the violet color, (6) the interference of vitamins Dz and