Comparative Studies on Spectrophotometric Determination of Selected Heavy Metals in Environmental and Biological Samples with Synthetic Phenylhydrazones as Chromogenic Reagents

Abstract

This work involves a comparative study on a simple, sensitive, selective and non-extractive Uv- Vis spectrophotometric method for the determination of cadmium, lead, chromium and arsenic in biological, soil and water samples using synthesized and characterized phenylhydrazones; [glutaraldehyde phenylhydrazone (GPH) and acetylpyridine-2,4-dinitrophenylhydrazone (APDH)] as the chromogenic reagents was developed. GPH and APDH were synthesized as new chromogenic analytical reagents for the direct UV-Vis spectrophotometric determination of the selected metals of interest in a slightly acidic pH of 6.5-7.5 and 20% dimethylformamide (DMF) solution to give stable coloured metal-ligand complexes. The reactions were instantaneous; the wavelengths of maximum absorptions were followed spctrophometrically and noted. The analytical properties of the reagent APGH on the metals (Cd, As, Pb, and Cr) revealed the wavelength of maximum absorption ranged between 385.0 (Cr) to 440.0nm for (Pb). The reagent APDH had molar absorptivities (L mol -1 cm -1 ) ranging from 2.006 x 10 4 (Pb) to 2.407 x 10 4 (Cd), a mole ratio of metal to ligand of 1:1, a detection limit (µg/g) ranging from 0.3272 (As) to 0.4456 (Cd) and the metal-ligand complex was stable for 0-36 hours. The reagent GPH revealed a wavelength of maximum absorption between 360.0 (Cr) to 395.0 nm for (Pb and As) at a working pH of 6.5 to 7.5 room temperature (37°C). The reagent GPH had a molar absorptivities (L mol -1 cm -1 ) ranging from 2.213 x 10 4 (Pb) to 2.460 x 10 4 (As), a mole ratio of metal to ligand of 2:1, the detection limit (µg/g) ranging from 0.3432 (As) to 0.5250 (Pb) and the metal-ligand complex was stable for 0-48 hours. Both reagents had a Beer’s law validity range (mgL -1 ) of 0.001 to 100. The Sandell’s sensitivities (µg/cm 2 ) ranged from 0000409 (As) to 0.00499 (Pb) for APDH and 0.00406 (As) to 0.00452 (Pb) respectively. Large excess of cations and anions as possible interferences up to 1