The product was characterized by elemental and spectral analysis. Its solution was prepared in Dimethylformamide (DMF).

A stock solution of Co(II) was prepared by dissolving accurately weighed cobalt sulphate in water containing sulphuric acid and it was standardized by Nitroso-R-Salt method⁹. Working solutions of Co(II) were made by diluting the stock solution to an appropriate volume. All other reagents used were of AR grade and all the solutions were prepared in doubly distilled water

Procedure for the Extraction and Separation of Cobalt (II):

An aliquot of aqueous solution containing 500 µg of Co (II) and 2 ml of 2% solution of NOMBAP prepared in DMF were mixed in 25 ml beaker. The pH of solution was adjusted to the desired value with dilute solution of HCl /NaOH, keeping the total volume to 10 ml with distilled water. The resulting solution was first digested on a boiling water bath for 15 minutes, cool and then transferred into 125 ml separatory funnel. The beaker was then washed with 5 ml portion of organic solvent and each washing was added to the solution in the separatory funnel. The two phases were equilibrated for 1 minute and allowed to separate. After the separation of two phases, pH of the equilibrated aqueous phase was measured and cobalt content in each phase was estimated by Nitroso-R-Salt method⁹. The extraction was carried out with different solvents to find out the best extracting solvent.

Procedure for the Extractive Spectrophotometric Determination of CO (II):

To an aliquot of aqueous solution containing 1.0-30µg of Co (II), 2ml of buffer solution of Ammonium chloride and ammonium hydroxide pH 9.0 and 2 ml of 2% solution of NOMBAP prepared in DMF were added. The volume of solution was made up to 10 ml with distilled water. The resulting solution was first digested on a boiling water bath for 15 minutes, cool and then transferred into 125 ml separatory funnel. The beaker was then washed twice with 5 ml portion of organic solvent and each washing was added to the solution in the separatory funnel. The two phases were equilibrated for 1 minute and allowed to separate. The chloroform extract was collected in a 10 ml standard measuring flask and made up to mark with chloroform, if necessary. The absorbance of chloroform extract was measured at 490 nm against a reagent blank prepared under identical conditions. The measured absorbance was used to compute the amount of Co (II) present in the sample solution from predetermined calibration Curve. To study the effect of other ions, the respective foreign ions were added to aqueous phase before the extraction and adjustment of pH.

Procedure for the Determination of Cobalt (II) in pharmaceutical sample:

If 0.5 g of pharmaceutical sample of was dissolve in boiling with 10 ml of aquaregia. The solution was evaporated to dryness and residue was dissolve in 10ml of 1M HCl filter, The resulting solution was diluted to 250 ml of D/W. 1ml aliquot of this solution was analyzed for Co (II) by procedure as describe earlier.

Determination of Cobalt (II) in high-speed alloy sample:

If 0.5 g of alloy sample of was dissolve in boiling with 10 ml of aquaregia. The solution was then evaporated to dryness and residue was dissolve in 5ml of dilute HCl. The resulting solution was diluted to 250 ml of distilled water. The aliquot of this solution was treated with 1ml of 0.5ml NaF to mask Cr (III) and 1ml of triethanolamine to mask Fe (III). 1ml aliquot of this solution was use for analysis of Co (II) by procedure as describe earlier.

RESULTS AND DISCUSSION:

Co (II) could be extracted quantitatively (99.53%) by NOMBAP into Chloroform from an aqueous solution of pH 8.2 to 9.5 in presence of 3ml of Ammonium chloride Ammonium hydroxide [Fig I] .Organic solvents used for extraction of Co (II) can be arranged on the basis of their extraction coefficient values as chloroform > Ethyl acetate> carbon tetrachloride > n-butanol > Chlorobenzene > Bromobenzene > benzene > Xylene [Fig II]. Chloroform was found to be the best extracting solvent hence; it was selected for the extraction throughout the work. The Chloroform extract of Co: NOMBAP complex showed an intense peak at 490 nm [Fig - III]. The absorbance due to the reagent is negligible at this wavelength, so the absorption measurements were taken at this wavelength. The result shows that the system confirmed to Beer’s law at this wavelength over a Co (II) concentration range of 0.1 to 3.0 µg/ml [Fig -IV]. The molar absorptivity of the extracted complex on the basis of Co (II) content was calculated to be 1385.6 L mol^–1cm^–1. It was found that 2 ml of 2.0% DMF solution of NOMBAP was sufficient to extract 30µg of Co (II). The colour of the Chloroform extract was found to be stable at least 24 hrs. at room temperature.

Fig -I

Solution A: Absorbance spectra of NOMBAP

Solution B: Absorbance spectra of Co–NOMBAP Complex

Calibration of Co(II)

Fig –II

Effect of other ion:

Co (II) (20g) was determined in the presence of various ions. The following ions in the amount indicated, did not interfere in the spectrophotometric determination of Co (II):

10 mg each of Li(I), Ba(II), Hg(II), Sn(II), Ca(II), Ti(III), Bi(III), Pb (II), Zn(II), Sr(II), Zr(II), V(V), Cd(II), Mg(II) and Mo(IV).

Table – I

Sr. No.	Interfering Ions	Amount added in mg	Masking agent added 1ml of 0.5 M solution	Absorbance
1.	Ni(II)	10	S-Sulphosalicylic acid	0.45
2.	Cr(III) & Mn(II)	10	Sodium Fluoride	0.45
3.	Ag(I)	10	Pottasium thiocynate	0.45
4.	Fe(II) & Fe(III)	10	Triethanol amine	0.45
5.	Cu(II)	10	Sodium dihydrogen phosphate	0.45
6.	Oxalate	10	Sodium Molybdate	0.45

5 mg each of Th (IV), Ce (IV) and W (VI).

0.1mg each of Ru (III), Rh (III) and Pt (IV).

20 mg each of chloride, bromide, Iodide, Fluoride, sulphate, Sulphide, nitrate, nitrite, phosphate, Thiocynate, acetate, Citrate, Triethanol amine and 5-sulphosalicylic acid.

Interference by the various ions were removed by using appropriate masking agent (Table - I).

Composition of the Extracted Complex:

The composition of the extracted complex was found to be 1:2 (Co: NOMBAP) by Job’s continuous variation [Fig - III] and Mole ratio methods. [Fig - IV]

Fig-III

Fig - IV

Precision, Accuracy, Sensitivity and Applications of Method

The precision and accuracy of the method were tested by analyzing the solution containing a known amount of Co (II) following the recommended procedure. The average of 10 determination of 10 µg of Co (II) in 10 cm³solutions was 9.96 µg, which is varied between 9.93 and 9.99 at 95% confidence limit. Standard deviation and Sandell’s sensitivity of the extracted species is found to be ±0.04 and 0.0425 µgcm^-2respectively. The proposed method has been applied for the determination of Co(II) in alloy samples. The results of the analysis of the samples were comparable with those obtained by the standard method¹⁴for Co (II) (Table - II).

Table – II

Commercial Samples	Cobalt (II) found *(%)
Commercial Samples	Present method	Standard method⁹
Pharmaceutical (Becousules capsule)	14.45 %	14.61%
High-speed alloy	46.14%	46.182%

* Average of three determinations

CONCLUSIONS:

The extractive spectrophotometric determination of Co (II) was successfully carried out. The reagent NOMBAP formed complex with cobalt (II) which were easily extracted into organic phase. The method is simple and reliable. Experimental conditions for maximum extraction was determined and applied for the analysis of samples.

ACKNOWLEDGEMENT:

Authors are thankful to the Principal Dr. (Mrs.) J. K. Phadnis, V.E. S. College of Arts, Science and Commerce, Sindhi Society, Chembur, Mumbai-71 for providing necessary research facilities.

REFERENCES:

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4. Feig F. Chemistry of specific, selective and sensitive Reactions Oesper RE. English Ed. New York 1949.

5. Mirzaeva KA, Akhmedove MS and Akhmedov SA, Extraction and spectrophotometric determination of dimedrol and papavarine in pharmaceutical dosage forms. J. Analytical Chem. 59(1); 2004: 215 - 218.

6. Sanchez Gracia G., Bosch Raig F. and Estela J.M. Anal.Quim., Ser .B., 76;1980:273-275.

7. Puri B.K. Sethi C.L. and Kumar A., J.Chin. Chem. Soc. (Taipei), 29;1982:173-174.

8. Sawant A.D., Barhate V.D., Lokhande R.S., J. Indian Council of Chemists, Vol.27 (2);2010:215-216.

9. Sandell E.B. and Onishi H., Photometric Determination of Traces of Metals, Part-I, 4^th Edition, A Wiley Intersciences Publication, New York, (1978).

10. Vogel A.I., Practical Organic Chemistry. 5^th Edition.Lozyman Group Ltd., London (1989).

Received on 21.12.2013 Modified on 19.01.2014

Asian J. Research Chem. 7(3): March 2014; Page 300-303

INTRODUCTION:

EXPERIMENTAL:

Commercial