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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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Spectrophotometric determination of cobalt(II) was accomplished with vanillilfluorone (VF) in the presence of dimethylbenzyltetradecylammonium chloride (Zephiramine, Zep). In the determination of cobalt(II), Beer's law was obeyed in the range of 24-470 ng/ml, with an effective molar absorption coefficient (at 575 nm) and relative standard deviation of 1.35؋ ؋10 5 l mol ؊ ؊1 cm ؊ ؊1 and 0.66% (n‫؍‬ ‫,)5؍‬ respectively. The composition ratio of the colored complex was determined by the mole ratio and continuous variation methods, and it was found to be Co(II) : VF : Zep‫؍‬ ‫1؍‬ : 2 : 4. Analysis of cyanocobalamin by the same procedure showed that cyanocobalamin could be determined in the concentration range of 0.5-0.11 m mg/ml using the proposed method.

An improved method for the fluorophotometric determination of trace Al(III) has been developed. This method involves a fluorescence quenching reaction that results in the formation of an m-carboxyphenylfluorone-Al(III) complex in a poly(N-vinylpyrrolidone) micellar medium. The calibration curve was found to be linear in the range of 0.03-1.50 µg dm(-3). We successfully applied the proposed method to an assay of Al(III) in canned beverages, which required only sample dilution and no sample pretreatment. The proposed method is expected to determine Al(III) in a simple and rapid manner.