Studies on colour tests for sterols and for vitamin A

Abstract

The transient nature of the colors developed renders a true characterization of the absorption very difficult; this is particularly true with the AsCl3 reagent. It was found possible by rapid work on constantly renewed mixtures to obtain photographs, giving log Io/I values of 0.1-0.8, representing the vitamin colors as they appeared within little more than a minute of mixing. This method gave for 5 specimens of cod-liver oil and 2 concentrates a well defined absorption band at about 587[mu][mu]; the 2 concentrates also showed a second band at about 475[mu][mu]. The color with SbCl3 persists longer (under conditions used) and hence presents less difficulty; the blue color given by this reagent with 6 oils and concentrates showed an initial absorption band at about 614[mu][mu] and a band which developed on standing, at about 528[mu][mu]. There was a definite decrease in concentration of the chromogen producing the band at 614[mu][mu], simultaneously with an increase in the chromogen producing the other band. The importance of the "time effect" in any work on the color tests for vitamin A is emphasized; it is further pointed out that the colors and absorption bands which characterize them "cannot be considered specific until they can be obtained from a definite Jchemical compound which possesses the physiological properties of the vitamin.".