Specificity in tests for vitamin A. A new conception of the chromogenic constituents of fresh and aged liver oils

Abstract

The ideal conditions for accurate colorimetric determinations of vitamin A in liver oils and the characteristics of SbCl3 as a color-producing reagent are reviewed in detail. In a considerable number of oils characterized in the color test by predominance of the 572 m[mu] band over the 606 m[mu] band, a large increase in the intensity of the latter band can be obtained by treating the oil with ozonized oxygen, H2O2, or benzoyl peroxide. Oils which initially showed an excess of the 572 m[mu] chromo-gen over the 606 m[mu] chromogen underwent a slow spontaneous ageing which resulted in a marked increase in the intensity of the 606 m[mu] band, not at the expense of the 572 m[mu] chromogen and not accompanied by similar increases in the latter; the absorption at 328 m[mu] remained practically constant throughout. The reality of the two chromogens and the possibility of recording the 572-583 m[mu], band even in oils and concentrates in which the 606-620 m[mu] chromogen predominates can be demonstrated visually and photographically by a modification of the ordinary procedure in the color test, which suppresses or eliminates some of the 606 m[mu] chromogen. The bearing of the data on the vitamin A problem is discussed in detail, and the most plausible criteria for the vitamin are stated. The two main chromogens be-have as if they were separate and distinct entities but a close genetic relationship seems highly probable.