Photolytic microdetermination of vitamin A in blood serum.

Bessey et al. (1) reported a simple method of photolytic determination of vitamin A in as little as 0.06ml of blood serum and Jackson et al. (2) and Krause et al. (3) used this method for studies on serum vitamin A. Sahashi et al. (4) reexamined the method applying the apparatus and reagents available in the country. Sobel et al. (5) noticed too high values for carotene, when the method was applied to hemolyzed serum. Bieri et al. (6) observed that the optical properties of the kerosene-xylene reagent changed when it was not stored protected from light and noticed that serums showing evidence of he molysis should not be used. When the method is applied to the blood serum containing much carotene, especially when carotene isomerized by heating was injected, the value of vitamin A determined become too high due to a partial photolysis of the cartene. When much carotene is present in blood, the value E328mƒÊ/E455mƒÊ is determined, and from the E455mƒÊvalue the E328mƒÊ value due to carotene is calculated. By substracting the latter value from the E328mƒÊ value of the serum, the value for vitamin A is obtained. They also found that the values for vitamin A determined photolytically agreed fairly well with those by the Carr-Price method. The authors reexamined Sahashi's method and found the purification procedure of kerosene to be very difficult and an appropriate condition was established. They noticed further that the E328mƒÊ values of the kerosene-xylene reagent used by the authors rose in the course of ultraviolet irradiation and the correction due to the rise in blank test was necessary. An improved procedure is given in the following.