SPECTROPHOTOMETRIC METHOD FOR THE DETERMINATION OF ASCORBIC-ACID WITHIRON (III)-1,10-PHENANTHROLINE AFTER PRECONCENTRATION ON AN ORGANIC SOLVENT-SOLUBLE MEMBRANE-FILTER

A solvent-soluble membrane filter is proposed for the simple and rapid preconcentration and spectrophotometric determination of ascorbic aci d based on the reduction of 1, 10-phenanthroline (phen)-iron (III), wh ich is collected on a nitrocellulose membrane filter as an ion-associa te of the cationic complex of tri,phen-iron (II) [ferroin, Fe(phen)(3) (2+)] with an anionic surfactant (of dodecyl sulfate). The ion-associa te collected is dissolved in a small volume of 2-methoxyethanol togeth er with the filter. The colour intensity is measured at 510 nm against the reagent blank and is proportional to the content of ascorbic acid in the range 2.5-50 mu g ascorbic acid in 5 ml of solvent with excell ent reproducibility (RSD 3.2% for 200 mu g l(-1) ascorbic acid), the e nrichment factor achieves 100-fold and detection limits better than 2. 0 mu g l(-1) can be obtained. Diverse components of organic and inorga nic compounds normally present in fruits, vegetable, beverages and uri ne do not interfere. The recoveries of the ascorbic acid added to the samples are quantitative.