Lxii. the Determination of Vitamin D

THE stability of preparations of vitamin D is of importance, both for the commercial products now on the market, and especially for the standard solutions which are widely used in estimations of the activity of other preparations. At present the International Standard adopted at the London Conference in 1931 consists of a solution of irradiated ergosterol in olive oil, and although this is likely to be replaced within two or three years by preparations of the crystalline solid vitamin recently isolated, sub-standards of solutions in oil will probably continue in use for many years. Although it is well known that cod-liver oil retains its antirachitic activity for a long time, little work has been done on the stability of artificially prepared vitamin D. Steenbock and Black [1925] found that irradiated olive oil lost all activity in nine months when freely exposed to laboratory air, but retained its activity when kept in a stoppered bottle for the same period. We are, however, aware of no detailed work on the stability of irradiated ergosterol in oily solutions, and we therefore undertook the following tests. Owing to the considerable stability of vitamin D at room temperature, and the inaccuracy of current methods of estimation, tests of stability are difficult and laborious. Hence the tests described in this paper are admittedly incomplete. They do, however, show that preparations cannot be relied upon to retain their activity for a year at room temperature, and they give a rough guide to the probable keeping qualities of standard and other preparations. The majority of these tests were done at the request of the Vitamin D SubCommittee of the Accessory Food Factors Committee of the Lister Institute and Medical Research Council, in preparation for the International Conference of 1931.