Formation of ionic associates with pyrogallol complexes of antimony (III) and their application for spectrophotometric determination of antimony

Abstract

The possibility of using water soluble pyrogallol red (PRWS) as a photometric reagent for the quantitative determination of antimony (III) in real objects has been studied. Formation of a colored product is observed in acidic solutions (pH 3.8 - 4.5) with a weak oxidizing agent (iodine) present for preliminary oxidation of SbHg to salts of Sb (III). The excess iodine is eliminated through introduction of sodium thiosulfate solution after obtaining the photometric form. The maximum analytical signal of the colored form is observed at 378 nm (e = 5.936 x 103). A decrease in the acidity of the solution (pH > 7) is accompanied by the formation of sodium salts of the reagent which prevents further complexation, whereas the only one maximum in the absorbance within the recommended pH range directly indicates to the formation of the the only one ionic associate (AI). The ionic associate thus formed appeared low stability in time. Unfortunately, change in the dielectric constant of the solution failed to give a positive effect and measurements of the absorbance of the colored compound were limited to 3 minutes. Determination of the composition and possible mechanism of the ionic associate formation was carried out on using the methods of molar ratios and isomolar series. After stripping of stibine into the absorption system, an ionic associate of the composition M:R = 1:1 is formed with a calculated stability constant of 4.01 x 105. The obtained results are used to develop a spectrophotometric (SP) method for antimony determination with the limits of detection and quantitative determination of the element 1.30 and 4.32 pg/ml, respectively. The developed method is valid in terms of the specificity, linearity, precision and accuracy, and, therefore, can be recommended for determination of the antimony content in any control and analytical laboratory.