An Extractive pH Dependent Solid Phase Spectrophotometric ( SPS ) Determination of Mn ( II ) and Cu ( II ) by using N , N '-bis ( 5-( 4-nitrophenyl ) diazenyl )-2-hydroxybenzylideneamino ) Ethylenediimine ( NDHBDED ) Modified with Alumina

A new azo dye Schiff base ligand, namely 1, 1'-bis(5-(4-nitrophenyl)diazenyl)-2hydroxybenzylideneamino) ethylenediimine (NDHBDED) has been synthesized and it was impregnated with alumina for extractive determination of metal ions. In this report the sorbent matrix was used for extractive determination of Mn (II) and Cu (II) ions by solid phase spectrophotometric (SPS) method. Both the metal ions were extracted at pH 6.5 and 5.5 respectively. The complexes show maximum absorbance at l max 590 nm and 570 nm respectively for Mn (II) and Cu (II) ions. The Beer’s law range was 10-100 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 Mn (II) and Cu (II) were 2.351x10-4 L mol-1 cm-1 and 2.225x10-4 L mol-1 cm-1 respectively. The Sandell’s sensitivity was 0.004 μg/ cm2 and 0.008 μg/ cm2 for Mn (II) and Cu (II) ions respectively. The proposed method was successfully applied to the determination of each metal ion in real samples and tap water. key words: Azo dye Schiff base ligand, Mn (II) and Cu (II) complexes, Solid phase spectrophotometric (SPS).


INtroDuCtIoN
First transition series metals have wide spectrum of industrial applications, especially in steel, catalyst, alloy, electroplating, ceramics & petrochemical industries [1][2][3] .Some of them play important roles in the biology of micro-organisms, plants and human nutrient.Among heavy elements, Mn (II) and Cu (II) metal ions are problematic in human physiology [4][5] .
Manganese is widely distributed in earth crust and biological bodies.Though, manganese is one of the essential elements for human health and for other animal's kingdom as well as for plants [6][7][8][9] .Manganese plays an important role across the life span of all mammals.The role of manganese, as a required co-factor for enzymes and basically, in arginase, which is responsible for urea production in the lever, for superoxide dismutase, which is very important antioxidant enzyme.But its higher level is toxic for human health.It affects the central nervous system.Manganase not only affects the ecosystem, but it also causes erosion of household utensils, bath accessories, clothes and unpleasant taste in food, drinks [10][11][12][13][14] .
Another heavy metal copper is both vital and toxic for many biological systems.Although trace amount of copper is essential for many biological systems, but its higher concentration is an anthropogenic pollution.It plays a key role in the formation of hemocyanin which is an important respiratory protein.From the standpoint of human health, its role is involved in hemopoiesis and in maintenance of vascular and skeletal integrity and function of the central nervous system.It occurs naturally in most vegetables, meats, and grains.It plays a key role in regulating vital biological processes [15][16][17] .
In view from the above standpoints, the separation and determination of Mn ((II) and Cu (II) from different environmental matrices is of great importance.For the determination of both the metal ions at micro level there are several frequently adopted analytical techniques such as electrothermal atomic absorption spectrometry (ETAAS), AAS, inductively coupled plasma mass spectrometry (ICP-MS), X-ray fluorescence spectrophotometry, spectrofluorometry, and other such technique.Several methods such as liquid-liquid extraction, precipitation, cloud point extraction, co-precipitation and solid phase extraction etc. are used for preconcentration and separation of heavy metals.Out of these above method, the spectrophotometric methods are cheaper and easier to operate and have comparable sensitivity.

ExPErIMENtAl reagents and Solutions
High purity reagents were of analytical grade from E. Merck, Germany and other metal salts from BDH, India also were of analytical grade reagent.p-nitroaniline, salicyldehyde and ethylenediamine from Sigma and Aldrich were used for the preparation of the ligand and for the complexation.A neutral solid sorbent alumina was used for the determination of metal ions from Oxford Lab., Mumbai, India.Standard stock solutions of Mn (II) and Cu (II) (1mg/ml) were prepared by dissolving appropriate amount of pure grade chemicals in double distilled deionised water with addition of few drops of conc.HCl.The working solutions of metal ions were prepared by diluting appropriate volumes of stock solution with distilled water.The solution of the chelating agent was prepared in ethanolmethanol mixture.

Instrumentation
The UV-Vis spectra were recorded in ethanol-methanol mixture using Shimadzu Spectrophotometer (UV-1800).A mechanical shaker (BOD-incubator, YONA Mfg.Indian Instruments Manufacture Co., Kol-12) was used throughout the experiments.A labtronic pH meter (Model No-23) equipped with a combined glass-calomel electrode was used to monitor the pH of the solutions.

Synthesis of Azo dye Schiff base ligand (NDHBDED):
The ligand N, N'-bis(5-(4-nitrophenyl) d i a z e n y l ) -2 -h y d r o x y b e n z y l i d e n e a m i n o ) ethylenediimine (NDHBDED) was synthesized by our previous reported method.

(a) Azo coupling of salicyldehyde
Our proposed diazo compound was synthesized by a reported method.A suspension of p-nitroaniline (2.50 g, 20 mmol) in 30 ml HCl and 10 ml of water was heated from 60-70 0 C until complete dissolution.The clear solution was diazotized with NaNO 2 (2.5 g) dissolved in water ( 10 General Procedure 2 g of the azo dye Schiff base (NDHBDED) chelating reagent was impregnated on the surface of 4.0 g of alumina at the ratio 1:2 in ethanolmethanol mixture and stirred for 30 minutes at room temperature.The resulting composition was left in an oven at 60 0 C for 48 hours.After drying, the sorbent was ground into powder for metal ions extraction.For the batch method of extraction 300mg of sorbents were used in each 100 ml flasks with 25 ml of 0.01 (M) solutions of Mn (II) and Cu (II) ions and pH was adjusted to 6.5 using HCl (0.1 M) and NaOH (0.1 M) solutions.The mixture of the sorbent matrix and metal ions solutions were shaken vigorously by a mechanical shaker at room temperature for 30 minutes for adsorption of the metal ions onto the adsorbents.

rESultS AND DISCuSSIoN
UV-Vis spectra for NDHBDED shows maximum absorbance at l max 500 nm, but the spectra of the complexes of Mn (II) -NDHBDED and Cu (II) -NDHBDED give maximum absorbance at l max 590 nm and 570 nm respectively [Fig. 1 &  (II) in the conc.range of 10-100 µg and 10-100 µg respectively.The formula of the complexes of Mn (II) and Cu (II) were ascertained by Job's method and molar ratios methods as 1:1.The analytical parameters of the solid phase spectrophotometric determination of Mn (II) and Cu (II) are given in [Table 1].

Effect of pH
In the quantitative recovery of the metal ions in the solid phase spectrophotometric (SPS) determination pH is a very key factor.The effect of pH for the percentage of extraction of Mn (II) and Cu (II) was investigated at a range 2 to 7.5.The quantitative extraction (> 90 %) found at the pH 6.5 and 5.5 respectively for Mn (II) and Cu (II).Hence, both of the above pH was chosen for the respective metal ions for further studies.Effects of pH on the percentage recovery of the metal ions were shown in Fig. 3.

Effect of temperature
The influence of the temperature on the percentage of extraction of 10 µg/ml of each Mn (II) and Cu (II) was studied in the range of 20-60 0 C at pH range 5.0 -6.5.The results showed in Fig. 4, that the maximum percentage of sorption of Mn (II) is found at 30 0 C and Cu (II) is found at 35 0 C. Hence, for the extraction of both the metal ions, the temperature range was chosen for further studies.

Effect of amounts of NDHBDED
The effect of the reagent concentration impregnated with alumina on the quantitative extraction of metal ions was studied in the range of 0.1 to 1.0 mg.Results show that the extraction of the sorbent was increased on the addition of the reagent.The optimum amount of NDHBDED is at 0.5 mg, where more than 95 % of the metal ions extracted.The results are given in Fig. 5.

Effects of metal ions concentration
The percentage extraction of the metal ions in the range of 10-100 µg/ml was studied at a fixed amount of the ligand (0.5 mg) on the solid matrix at pH 6.0.Almost 90 % of both the metal ions were extracted by the sorbent [Table 2].The stoichiometry of the complexes with Mn (II) and Cu (II) ions were determined by Mole-Ratio method and by Job's method of continuous variation at fixed absorbance of l max 500 nm.

(a) Mole-ratio method
The extraction of the metal ions were studied in the range 0.1 to 1.0 mg of the ligand concentration.The nature of the curves were straight line for both the metal ions which predicting the nature of the complexes are 1:1.The results shown in Fig. 6.

(b) Job's method of continuous variation
For fixed volume of the ligand concentration (0.5 mg) with the different concentration of the metal ions 10 -100 µg/ml were studied.The natures of the curves predicting the nature of the complexs are 1:1.The results are shown in Fig. 7.

Effects of Divers ions
The effects of various foreigns ions on the determination of Mn (II) and Cu (II) under optimum conditions was studied.The tolerance of the method of foreigns ions was investigated with solutions containing 1µg/ml each of Mn (II) and Cu   3.

Effects of Eluents
Varoius volumes of different eluents were applied for determination of Mn (II) and Cu (II) under optimum conditions.For satisfactory results 3M HNO 3 has been used.Various volume of HNO 3 was used for extraction of each metal ions and it was found to increase by increasing its volumes.The results is shown in Table 4.

Analytical Application of the proposed method
Optimum pH subjected to the solid phase spectrophotometric (SPS) determination of each metal ions show the results as reported in Table 5.It clear that, the proposed method is suitable for Mn (II) and Cu (II) determination in real samples like tab water.

CoNCluSIoN
A simple and sensitive solid phase spectrophotometric method for the determination of Mn (II) and Cu (II) ions based on complexation.The method has been applied for the determination of these two metal ions in real samples and tap water.The wide applicability and simplicity of the proposed make it different from other existing methods.

Fig. 7 :Fig. 5 :Fig. 6 :
Fig. 7: Job's continuous variation method . Few metal ions, such as Fe (III), Ni (II), Zn (II) and Pb (II) interfere only when present in the same concentration range.The results are presented in Table