Extractive Determination of Co ( II ) and Ni ( II ) by N , N '-bis ( 5-( 4-nitrophenyl ) diazenyl )-2-hydroxybenzylideneamino ) ethylenediimine ( NDHBDED ) Impregnated with Alumina by pH Dependent SPS

A new azo dye Schiff base analytical reagent, namely N, N' -bis(5-(4-nitrophenyl)diazenyl)2-hydroxybenzylideneamino)ethylenediimine (NDHBDED) has been synthesized and it was impregnated with alumina for extractive determination of metal ions. In this report the solid sorbent matrix was used for the extraction of Co (II) and Ni (II) ions by pH dependent SPS method. The maximum molar absorbances were at 445 nm and 508 nm at pH 4.5 and 5.0 for Co (II) and Ni (II) ions respectively. The Beer’s law range was 5-100 μg/ml for both the metal ions. Job’s method and mole-ratio method showed that metal-ligand ratio in the complexes to be 1:1. The Molar absorptivity for Co (II) and Ni (II) were 1.351x10-4 L mol-1 cm-1 and 1.925x10-4 L mol-1 cm-1 respectively. The Sandell’s sensitivity was 0.005 μg/ cm2 and 0.004 μg/ cm2 for Co (II) and Ni (II) ions respectively. The proposed method was successfully applied to the determination of each metal ion in real samples and tap water. keywords: Azo dye Schiff base analytical reagent, Co (II) and Ni (II) complexes, pH metric SPS.


INTRODUCTION
The determination of metal ions in natural samples is very important part of environment and human health [1][2][3][4] .Metal ions-ligands coordination complexes are the intense analytical approach for the determination of metal ions of the environmental samples [5][6][7][8] .Some metal ions are constituents of the metabolic enzyme in biological system, but their toxicity influence for direct determination in environmental samples.Cobalt and nickel are most common transitions metals.The significance of cobalt as transitions metal lies in its wide spectrum of applications such as in industries and consumers products.Another transition metal nickel is vital and its compounds are toxic for many biological systems.It can be considered is one of the frontier elements in the alloys industries for stainless steels, cast iron, german silver and monel metal and also found in many heat resistant alloys.It also plays vital roles in the biology of micro-organisms, plants and is an essential element in human diet [9][10][11][12][13] .L i t e r a t u r e s u r vey r eve a l s s eve r a l instrumental techniques have been employed for the determination of Co (II) and Ni (II), such as spectrofluorimetry, X-ray fluorescence spectrometry, neutron activation analysis, atomic absorption spectrometry, inductively coupled plasma mass spectrometr y, chemiluminescence, of which UV-visible solid phase spectrophotometry is preferred because of its low cost, rapidity and easy handling [14][15][16][17] .Several methods such as liquidliquid extraction, micellar mediated extraction, coprecipitation, cloud point extraction, electrochemical extraction and solid phase extraction are adopted for metal ions extraction [18][19][20][21][22] .But disadvantages such as significant chemical additives, solvent losses, complex equipments, considerable secondary waste and time consuming problems limit the application of most of these techniques.Solid phase spectrophotometric (SPS), however, solves these problems as it offers several advantages.This technique is also attractive as this is no need to use organic solvents, which may cause toxic effects.
A wide variety of reagent has been reported for the spectrophotometric reagents for determination of Co (II) and Ni (II).Some reagents were identified, but they suffer low sensitivity, interference from diverse ions.The azo dye Schiff base compounds have been extensively studied because of their biological and structural importance.Several azo dye Schiff base ligands containing N 2 O 2 -donor site have been proposed as spectrophotometric reagents for metal ions [23][24][25] .The importance of these compounds lies mainly in their specific and selective reactions with metal ions which forms stable complexes.In the present report, we introduced a new azo dye Schiff base ligand N, N'-bis(5-(4nitrophenyl)diazenyl)-2-hydroxybenzylideneamino) ethylenediimine (NDHBDED) for selective solid phase spectrophotometric (SPS) determination of some heavy metal ions from environmental samples.We impregnated the azo dye Schiff base ligand with alumina for the complexation with Co (II) and Ni (II) ions prior to solid phase spectrophotometric (SPS) determination of these metal ions.

Instrumentation
The absorbance measurements were recorded using Shimadzu UV-Vis spectrophotometer (UV-1800) fitted with 1cm quartz cells.A mechanical shaker (BOD-incubator, YONA Mfg.Indian Instruments Manufacture Co., Kol-12) was used throughout the experiments.The pH measurements were carried out by a labtronic pH meter (Model-23) equipped with a combined glass-calomel electrode.

Reagents and Solutions
Extra pure reagents were of analytical grade from E. Marck, Germany and other metal

Influences of pH
The pH of the aqueous samples is the very important factor for the quantitative recoveries of the metal ions in the solid phase spectrophotometric (SPS) studies, the influences of pH of the analyte solutions on the recoveries of Co (II) and Ni (II) on the solid adsorbents in the pH range 2 -7.

Influence of temperature
The effect of temperature on the percentage of extraction of 5 ìg/ml of each Co (II) and Ni (II) was studied in the range of 20 -60 0 C at pH range 4.5 to 5.0.The results showed in Fig. 6, that the maximum percentage of sorption of both the metal ions is found at 35 0 C, Hence, 35 0 C was considered for the further studies.

Effect of reagent (NDHBDED) concentration
The effect of the reagent concentration impregnated with alumina was investigated in the range of 0.1 to 1.0 mg.The results showed that the extraction of metal ions was increased on the addition of the reagent.It was found that the quantitative extraction (> 90 %) at 0.5 mg.But beyond this range of reagent concentration does not influence on the extraction of the metal ions.The results are given in Fig. 7.

Effect of Co (II) and Ni (II) ion concentration
The percentage extraction efficiency of the metal ions in the range of 5-100 µg/ml was studied at a fixed amount of the reagent (0.5 mg) on the solid matrix at pH 5.0.Almost 87 % of both the metal ions were extracted by the sorbent [

The Stoichiometry of the Co (II) and Ni (II) -NDHBDED
The stoichiometry of Co (II) and Ni (II) -NDHBDED complex was determined by Mole-Ratio method and Job's method of continuous variation at fixed absorbance l max 500 nm.

Mole-Ratio method
The extractions of the metal ions were carried out in the range of 0.1 to 1.0 mg of the reagent concentration.The natures of the curves were straight line for both the metal ions which predicting of cobalt and nickel in various real samples and in environmental samples.The results are reported in [Table 5].

CONCLUSION
The proposed method is a selective, accurate and sensitive for the determination of Co (II) and Ni (II) ions based on complexation.The suggested method could be used for rapid determination of these two metal ions in real samples and tap water.The wide applicability and simplicity of the proposed method make it different from other existing methods.