Sensitive Spectrofluorometric Determination of Vanadium with Sodium 1,2-Dihydroxyanthraquinone-3-sulfonate in Cationic Micellar Medium

Abstract

A spectrofluorometric method is described for the determination of vanadium(V) based on its complexation reaction with sodium 1,2-dihydroxyanthraquinone-3-sulfonate in presence of hexadecyltrimethylammonium bromide. The fluorescence is monitored at 607 nm with excitation at 505 nm. The experimental variables and interferences in this determination have been studied. The detection limit is 3.0 ng ml-' and the linear range is between 10 and 1000 ng ml-'. The method has been applied to the determination of vanadium in clams and seawater with satisfactory precision.Keywords Spectrofluorometry, vanadium determination, sodium 1,2-dihydroxyanthraquinone-3-sulfonate, micellar mediumVanadium is an essential trace element to man and animals, possessing specific physiological functions.1 Generally, concentrations determined in land plants and animals are less than those found in marine forms.2 However, numerous reports have warned of the toxic effects of vanadium resulting from excessive industrial exposure and from emissions into the environment from refineries, iron, steel and chemical industries as a result of the combustion of petroleum derivatives, which contain vanadium in the form of porphyrin complex.3 The toxicity of vanadium compounds increases with valence, the pentoxide being the most toxic.In the literature a few methods for the fluorometric determination of vanadium(V) are described. The oxidation reactions of anthraquinone derivatives have been used for the determination of vanadium(V). The anthraquinones used were 1,4-diamino-5-nitroanthraquinone4, 1-amino-4-hydroxyanthraquinone5'6, sodium 4,8-diamino-l,5-dihydroxyanthraquinone-2,6-disulfonate7-9 and sodium 1,3-dihydroxy-4-aminoanthraquinone-2-sulfonate.10 In all cases, the oxidation products are formed under certain conditions: as strongly acidic media and high temperatures (80 -85° C).The sodium salt of 1,2-dihydroxyanthraquinone-3-sulfonic acid (Alizarin Red S, ARS) has been widely used as a photometric reagentll, but it only has been used for the fluorometric determination of boron12,13, aluminum and gallium14, niobium15 and molybdenum.13,16 Of these, t To whom correspondence should be addressed.the fluorescence intensity has been greatly enhanced for the determination of molybdenum and niobium by addition of a cationic surfactant. These micellar media can improve the fluorescence determination of metals, presenting several advantages over conventional homogeneous solution techniques including increased sensitivity, reduced interferences and enhanced experimental convenience.l7-19In the present work, a spectrofluorometric method for determination of vanadium is proposed. The fluorescence of the complex formed between Alizarin Red S and vanadium(V) is developed in the presence of a cationic surfactant and the influence of the concentration is studied.The method has been successfully applied to the determination of V in clams and seawater. Compared with other fluorometric methods, the proposed determination is quite sensitive, offers shorter analysis time...