In usual methods for refining a vitamin A concentrate (hereinafter referred to as the sample), vitamin A is more or less liable to be destroyed as it is subjected first to adsorpon to separate impurities and then to elution before obtaining a higher concentrate.
In search of technological improvement it occurred to the authors that acid clay, when weakened appropriately, could be economically used as an adsorbent of impurities so as to avert the destruction of vitamin A.
In the experiments a definite amount of aquatic solution of ammonia, urea or NaOH was added to acid clay. The mixture was dried, pulverised, and then heated at a certain temperature. The acid clay thus weakened was used as the material adsorbing impurities from the sample.
Two methods were employed in adsorbing impurities of the sample into the weakend acid clay; one was a normal column chromatography and the other was shaking or stirring.
The results of the experiments were as follows:
1) Under certain condition, it had been possible to concentrate vitamin A by the use of acid clay weakened with ammonia or urea (Tables 1 and 2). Nevertheless, further experiments proved that a constant activity could not be secured in these adsorbents.
2) When weakened with NaOH, however, acid clay showed a constant activity in removing a part of the impurities from the sample together with fishness and dark color. The best result was obtained when the weakened acid clay containing 3.5% NaOH was heated at150°C and used at the rate of 20 parts to 1 part of the sample. Along with this adsorbent the shaking or stirring method is recommended to be most economical and practical for industrial purposes (Tables 3-8).
3) With view to examining the refining efficiency, the compositions of the sample before and after carrying out the adsorption were determined on the basis of alumina chromatographic fractionation, and the results were compared as in Fig. 1 and Table 9. The weakened acid clay was capable of adsorbing entirely fraction III consisting only of the impurities. In fraction II which consisted of the impurities and vitamin A, both equally adsorbable to alumina, a greater part of the former was adsorbed by the weakened acid clay.
4)
Kanurma earth (a kind of clay used in gardening) weakened by KOH was also as effective as the NaOH weakened acid clay in adsorbing impurities (Table 10).
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