Characteristics of highly active vitamin A preparations

Abstract

IN a series of papers emanating from these laboratories during the past five years unequivocal spectroscopic data for vitamin A have been established, and the ground has been cleared for a final comprehensive attack on the problem of isolating the vitamin and establishing its constitution. The present communication embodies the results of work carried out during the last 18 months, and leads us to the view that a definite solution of the problem is now in sight, a view supported by the recent highly important and illuminating publications of Karrer, Morf and Sch6pp [1931, 1, 2], to which further reference will be made later. Vitamin A, both in liver oils and concentrates, exhibits a broad continuous absorption band in the ultraviolet , extending from 260 to 380 m,u, and exhibiting a maximum near 328 m,. The intensity of this band can easily be measured and used as a definite quantitative test for the potencies of oils and concentrates. Vitamin A also shares with a variety of polyene substances the power of giving a blue solution with a saturated solution of anhydrous antimony trichloride in chloroform. This colour test gains in specificity when the spectral absorption of the blue solution can be accurately described. As a matter of convenience attention may be concentrated on the points of maximum absorption described in terms of intensity and spectral location'. Thus the blue solution obtained with vitamin A exhibits two maxima at 617 and 583 mu respectively, the former being generally much more intense than the latter, which it tends to mask. In unsaponified oils the maxima are displaced to 606 and 573 m, respectively, and here the longer wavelength absorption 1 The notation used in this paper is necessarily a little different from that employed in spectroscopic studies on pure substances. The usual method is to state the maximum molecular extinction coefficient e, defined by E =log Io/I =ecd. (Io is intensity of incident light, I is intensity of emergent light, E is extinction, c = molar concentration, d = thickness in cm.) In this work El, refers to log IO/I at a wavelength maximum, using a solution containing 1 % of vitamincontaining substance and a 1 cm. cell.

The variation of the extinction coefficient of vitamin A with solvent

“…These were all prepared from halibut liver oil (several different specimens) by hot saponification followed by removal of sterols by crystallization from alcohol, first at 00 and then at -60°, the product being finally purified by high vacuum distillation [cf. Heilbron et al 1932], or chromatographically on alumina or lime [Karrer & Morf, 1933;Castle et al 1934].…”

“…(d) Butter. The spectrophotometric method provides a useful means of assaying the vitamin A in butter via its unsaponifiable fraction but not on the original fat [Heilbron & Morton, 1930;Gillam et at. 1933], and both alcohol and chloroform have been used as solvent for this purpose [Baumann & Steenbock, 1933;Gillam, 1934].…”

Vitamin a in Eye Tissues

“…A 1 per cent chloroform solution of the purest vitamin A preparations has an extinction coefficient at 328 m# of about 1350, when in a layer 1 cm. deep (Heilbron, Heslop, Morton, and Webster, 1932). Since the extinction coefficient is directly proportional to both the concentration and the depth of the absorbing layer, the concentration of any unknown vitamin A solution may be computed from these figures.…”

Variations in the quality of butter, particularly in relation to the vitamin A, carotene and xanthophyll content as influenced by feeding artificially dried grass to stall-fed cattle

“…It has been established [Karrer, Morf and Schopp, 1931;Heilbron et al, 1932] that vitamin A is a colourless unsaturated alcohol characterised by a broad absorption band, free from fine structure, extending over the region 280-370 m,u approximately, with a maximum near 328 mp in alcohol at an intensity El "-= 1600 [Carr and Jewell, 1933] (the molecular extinction coefficient calculated on C20H30O/5 is probably close to 46,000 for alcoholic solutions). In any medium not exhibiting appreciable absorptive power at 328myk, it is easy to determine quantitatively the proportion of vitamin A in solution by measuring the extinction at 328m, for a given solution and cell thickness.…”