Determination of trace Zn (II) ION by forming metal-ligand chelate complex in aqueous medium using UV-VIS spectrophotometric method

Abstract

Trace amount of Zinc has been determined by spectrophotometric method using 1,2-dihydroxy anthraquinone-3-sulphonic acid sodium salt (Alizarin Red S) as a spectrophotometric reagent. The ligand Alizarin Red S reacts in slightly acidic solution (pH 4.00±0.02) with Zinc to give an orange-red chelate that has an absorption maximum at 502.2 nm. The reaction is instantaneous and absorbance remained constant for over 48 hrs. The average molar absorption co-efficient was found to be 2.1x102 Lmole-1cm-1. Linear calibration graphs were obtained for 0.30-100 μg mL-1 of Zn. The stoichiometric composition of the chelate has been found 1:2 (Zn:ARS). Large excess of cations, anions and some complexing agents have been studied. The method was successfully used in the determination of Zinc in several standard reference material, alloys & environmental water and made a comparison with those obtained by Atomic Absorption Spectrophotometer.