title: [The formation of cis-isomers of all trans-vitamin A acetate during the alkylation step for determination of vitamin A in feeds].
abstract: The determination of vitamin A in animal feed by HPLC must be preceded by a saponification step in order to eliminate the interfering lipids. This operation bears the risk of isomerisation of the vitamin A. We have determined the degree of isomerisation by adding trans-vitamin-A-acetate (in dry powder form) to 8 different vitamin A free blends, followed by saponification, extraction and HPLC. In this study, we have taken into account all the 5 known cisisomers. The degree of isomerisation depends on the type of feed and on the conditions of saponification and ranged from 4 to 40%. Pure vitamin-A-acetat was isomerised to the extend of 1 to 30% depending on saponification conditions. The recovery rate was (with some exceptions) 90 +/- 5%.
mesh_terms: D000478:Alkylation; D000821:Animal Feed / Q000032:analysis*; D055598:Chemical Phenomena; D002621:Chemistry; D002851:Chromatography, High Pressure Liquid; D004224:Diterpenes; D000084562:Retinyl Esters; D013237:Stereoisomerism; D014801:Vitamin A / Q000031:analogs & derivatives* / Q000032:analysis
chemical_list: D004224:Diterpenes; D000084562:Retinyl Esters; D014801:Vitamin A; C009166:retinol acetate
vernacular_title: Untersuchungen zur Bildung von cis-Isomeren aus all-trans-Vitamin-A-Acetat während des alkalischen Aufschlusses bei der Bestimmung von Vitamin A in Futtermitteln.