Sensitive spectrophotometric determination of ascorbic acid in pharmaceutical samples and fruit extracts

A highly sensitive spectrophotometric method for the assay of ascorbic acid is described. The procedure is based on the two-phase oxidation of ascorbi c acid by iodine in carbon tetrachloride. The formed iodide ions were react ed with a known excess of silver ions. The unreacted silver ions were utili zed for the formation of an intensely coloured ternary ion-pair complex wit h 1,10-phenanthroline and 2,4,5,7-tetrabromofluorescein which shows an abso rption maximum at 550 nm. The absorption of the colour system was found to exhibit a linear decrease with the increasing concentration of ascorbic aci d. The colour system obeys the Beer's law for 0-25 mu g of ascorbic acid in an over-all aqueous volume of 25 mi. The molar absorptivity and RSD were c alculated to be 9.1 x 10(4) l mol(-1) cm(-1) and 2.7% (n = 10), respectivel y. The proposed method was successfully applied to the determination of asc orbic acid in pharmaceutical preparations and fruit extracts. The reliabili ty of the assay was established by parallel determination by the standard i odimetric method and recovery studied of the added ascorbic acid.