Abstract
The benzene extraction method of vitamin A assay, introduced by F.J. Mulder of Philips-Duphar, was compared with the J.P. VII method in 16 laboratories, applying to several kinds of preparations : J.P. vitamin A referance standard solution, dry formed vitamin A, jelly, powdered multivitamins and cod liver oil. The benzene extraction method gave 2% higher value than the J.P. VII method in oil types, and 3〜5% in solid types. The results suggest that benzene dissolves into ethanol・water layer in some extent, and consequently vitamin A is concentrated in benzene layer. In both methods, absorption curves of extracts by ether or benzene were similar in isopropanol and also standard deviations of assay values were not significantly different, Instrumental error was examined by determination of the absorbance of a solution of 2-phenylazo-p-cresol in isopropanol with 17 spectrophotometers. The standard deviation of the absorbance (about 0.5) at 325 mμ was about ±1%.
