Spectrophotometric Determination of Ascorbic Acid with Iron(III) and p-Carboxyphenylfluorone in a Cationic Surfactant Micellar Medium

Abstract

1 is an important vitamin which participates in a great variety of biological events concerning electrontransport reactions, hydroxylations, the oxidative catabolism of aromatic amino acids and so on. Numerous papers and reviews 2-5 have described the determination of AA. The methods used include titrimetric, spectrophotometric, fluorometric, electrochemical, chromatographic, kinetic and chemiluminescent procedures. Photometric methods continue to be of interest because of ease in accessibility and their quick applicability to routine analyses. The majority of these methods are based on their oxidation-reduction properties or ability to couple with diazotized aniline derivatives. Many spectrophotometric methods based on the reduction of iron(III) to iron(II) with AA, followed by complexation of reduced iron(II) with different reagents, such as 1,10-phenanthroline (phen) and 2,2′-dipyridyl, have been reported. Another fast and facile method based on a proportional decrease in the absorbance of iron(III) complexes by the addition of AA has been proposed by some authors. On the other hand, AA has several donor atoms capable of metal complex formation and binding 6,7 with zinc(II), manganese(II), cadmium(II), alkaline earth metals and so on.We have already reported 8-10 on simple and sensitive determinations of various organic compounds utilizing a mixedcomplex system among an organic compound, a metal ion and a dye. Here, we have studied the color reaction of AA based on a coupled redox-complexation reaction among iron(III), xanthene dye and AA; also, a simple and highly sensitive spectrophotometric determination of AA was investigated by using iron(III) and p-carboxyphenylfluorone (PCPF) as a dye in the presence of a cationic surfactant. The proposed method was then applied to assays in pharmaceutical preparations. Experimental Reagents and solutionsAA and dehydroascorbic acid (DHAA), analytical-grade reagents, were purchased from Wako Pure Chemical Co. Ltd., and used without further purification. The stock and working solutions of AA were freshly prepared every day. DHAA was prepared daily not more than 2 h prior to use by dissolving DHAA in water. A solution of iron(III) (5.0 × 10 -4 M, 1 M = 1 mol dm -3 ) was prepared by dissolving a calculated amount of ferric ammonium sulfate in 100 cm 3 of water containing 1 cm 3 of hydrochloric acid (HCl) and a 10-fold molar excess of sodium fluoride over iron(III). A 1.0 × 10 -3 M solution of PCPF, which had been synthesized according to a method described in the literature, 11,12 was prepared in methanol containing one drop of HCl. A 1.0 × 10 -2 M solution of ntetradecyltrimethylammonium chloride (TTAC) was prepared in water. A buffer solution of pH 8.5 was prepared by mixing 0.1 M HCl and 0.1 M 2-amino-2-(hydroxymethyl)-1,3-propanediol (Tris) solutions. All other reagents and materials were of analytical grade, and were used without further purification. Pure water was prepared by purifying deionized water with a Milli-Q Labo System just before use. ApparatusA Shimadzu (...

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