Photometric Determination of Cobalt (II) after Adsorption of its 1-Benzoyl-3-(2-pyrimidyl) thiourea Complex on Polyurethane Foam

 

Shalini Verma¹, S. P Mathur², Savita Verma³

¹Department of Biotechnology, Chandigarh Group of Colleges, Landran, Mohali (Punjab)

²Department of Pure and Applied Chemistry, Maharshi Dayanad Saraswati University, Ajmer

³Department of Chemistry, Sophia Girls College Ajmer

*Corresponding Author E-mail: shaqrs@yahoo.com, sv52898@gmail.com, shalini.3203@cgc.edu.in

 

 

INTRODUCTION:

Cobalt has been known for its high industrial importance due to its ability of alloying, magnetic catalytic and plating properties. It is also an active centre of coenzymes¹

 

Complexation reaction of thiourea, thiols and other sulphur containing ligands have recently been investigated and reported as specific analytical organic reagents in photometric determination of trace amount of a number of metals because of their high sensitivity and selectivity and selectivity towards metals^. A study of literature reveals that numerous photometric reagents have been reported for the determination of trace amount of Cobalt (II)^4-7

 

 

Newly synthesized organic reagent i.e 1-benzoyl-3-(2-pyrimidyl) thiourea has been found to react with many metal ions to give the colour reactions of analytical importance.^2-3 The present study describes a sensitive and selective method for the photometric determination of cobalt (II) using 1-benzoyl-3-(2-pyrimidyl) thiourea as a complexing reagent.

 

In present investigation a new method called analysis of metals by solid-liquid extraction by the use of polyurethane foam as an absorbent as reported by Brown⁸ has been used for the photometric determination of cobalt (II). This method has many advantages over the usual liquid-liquid extraction as this method is very convenient, less time consuming and possesses a high degree of precision.

 

EXPERIMENTAL:

All chemicals used were of Analytical reagent grade. A standard stock solution of cobalt (II) (1000 ppm) was prepared by dissolving requisite amount of hydrated cobalt nitrate in 1000 ml of distilled water. Sample solutions of lower concentrations are prepared by appropriate dilution of required volume of stock solution. A 0.2% solution of 1-benzoyl-3-(2-pyrimidyl) thiourea is prepared by dissolving 0.2 gm of reagent in 100 ml of ethanol.

 

Polyurethane foam (Commercial U foam) pieces of 1 cm³ size were prepared by the method of Hamon et al⁹. The foam pieces were first soaked in 1 M hydrochloric acid for about 1.0 hours for the removal of all possible inorganic contaminants. The pieces were rinsed thoroughly with distilled water, squeezed and air dried at room temperature and dried pieces were ready for use. The polymeric properties were found to remain intact as a result of these treatments.

 

A GS- 5701 EC Spectrophotometer and Systronics digital pH meter Model No 335 were used for absorbance and pH measurements respectively.

 

An aliquot of standard solution of cobalt (II) 2.5 ml reagent solution is added. pH of the solution is adjusted to 4.0 by adding 4.5 ml of acetate buffer solution. The solution is diluted to 10 ml with distilled water. The contents are allowed to stand for two minutes for complete development of colour. Six polyurethane foam pieces of uniform sizes are added into the coloured complex. The flask is stoppered and shaken vigorously for two minutes to allow complete adsorption of complex so formed on polyurethane foam. Adsorbed complex from foam pieces is squeezed out manually with a glass plunger and is then taken in a glass beaker. Here traces of reagent are further squeezed out. The complex is eluted by squeezing foam pieces with two portions of 5.0 ml chloroform. Anhydrous sodium sulphate is further added to remove traces of water. The maximum absorbance is measured is a one cm cell in the wavelength region 380-620 nm against reagent blank prepared in the similar manner. Calibration curve is constructed under similar conditions.

 

RESULTS AND DISCUSSION:

Absorption Spectra:  

The absorption spectra of cobalt (II) complex of 1-benzoyl-3-(2-pyrimidyl) thiourea containing 90 µg of cobalt (II) was measured over the wave length region 380- 620 nm against reagent blank solution. The maximum absorbance is observed at 460 nm whereas absorption due to reagent blank is negligible at this wavelength. Hence, 460 nm is chosen as the most suitable wavelength to carry out all absorbance measurements

 

Effect of pH:

The effect of pH on the absorbance of cobalt (II) complex solution having 90 µg of cobalt (II) was investigated at 460 nm in the pH range 1.0-9.0 initially the absorbance shows an increase with increase in pH of the solution then it attains maximum and a constant value over the pH range 2.0-6.0. Further with increase in pH beyond 6.0 the absorbance is found to decrease sharply. Therefore pH of the solution is adjusted to 4.0 for all absorbance measurements

 

Table No 1:  Effect of pH

Cobalt (II) : 90 µg

0.2% Reagent Solution : 2.5 ml

Polyurethane foam : 6 pieces

 

Fig No 1: Effect of pH

 

 

Effect of Buffer solution:

The effect of buffer solution on the absorbance measurements of cobalt (II) complex solution was observed by adding varied columns of acetone buffer solution to a sample solution containing 90 µg of cobalt (II).  The addition of 2.5 to 6.0 ml of acetate buffer solution exhibits almost constant and maximum absorbance. Therefore, 4.5 ml of acetate buffer solution is preferred to be added for all absorbance measurements

 

 

Table No 2: Effect of Buffer solution

Cobalt (II) : 90 µg

0.2% Reagent Solution : 2.5 ml

Polyurethane foam : 6 pieces

pH : 4.0

 

Fig no 2: Effect of Buffer solution

 

Effect of Reagent Concentration: 

The reagent concentration was studied by adding different amounts of reagent solution to a sample solution containing 90 µg of cobalt (II) at pH 4. The absorbance increases up to the addition of 1.5 ml of reagent solution and becomes practically constant and maximum over the concentration range 1.5- 5.0 ml of reagent. Further the absorbance is decreased on adding more than 5.0 ml of reagent solution. Hence, 2.5 ml of 0.2% reagent solution was taken for all absorbance measurements 

 

Table No 3: Effect of Reagent Concentration      

Cobalt (II) : 90 µg

Polyurethane foam: 6 pieces

pH: 4.

 

Fig No 3: Effect of Reagent Concentration

 

Effect of adsorbent: 

The absorbance was found to absorbance dependent. For this purpose different numbers of prepared polyurethane foam pieces of uniform size was been added into 10.0 ml sample solution of cobalt(II) complex containing 90 µg of cobalt (II). Adsorbed cobalt (II) complex on foam pieces are then dissolved in 10 ml chloroform and absorbance is measured at 460 nm. Maximum nearly constant absorbance was observed at 460 nm wavelength with 3 to 9 pieces. The value of absorbance decreases on adding more than eight prepared foam pieces. So six prepared pieces of polyurethane foam was used to extract cobalt (II) complex for all absorbance measurements

 

Table No 4: Effect of Adsorbent                                  

Cobalt (II) : 90 µg

0.2% Reagent solution : 2.5 ml

pH : 4.0 .

 

Fig No 4: Effect of Adsorbent

 

Calibration Curve:

Based on optimum condition as specified the calibration curve was obtained for cobalt (II) determination. The curve was found to be linear and obeys beer’s law over the concentration range 201-120 µg of cobalt (II) present in 10.0 ml of chloroform. The molar absorptivity and sensitivity was found to be 3.38 x 10⁴ dm³ mol^-1 and 0.0.16 µg cm^-2 of cobalt (II) for the absorbance of 0.001 respectively.

 

Effect of diverse Ions:

Possible interference due to the presence of various alkali metal ions and diverse metal ions in the sample solution of cobalt (II) complex containing 90 µg of cobalt (II) was examined and results are summarized in Table no 5

 

Table No 5: Effect of Alkali Metal Ions       

S. No	Alkali Metal Ions	Amount Added (mg)	Cobalt (II) Found (g)
1	NaNO3	70	90.2
		140	90.8
2	KNO3	50	90.8
		100	91.3
3	Na2CO3	40	89.7
		100	90.4
4	K2CO3	60	91.5
		150	89.3
5	KCl	100	90.7
		200	90.3
6	NaCl	150	90.5
		200	89.2
7	K2SO4	80	89.7
		150	90.4

Cobalt (II) : 90 µg

0.2% Reagent solution: 2.5 ml

pH: 4.0 .

Polyurethane Foam: 6 Pieces

 

 

Fig No 5: Effect of Alkali Metal Ions  

 

Table No 6: Effect of Diverse Metal Ions       

S. No	Diverse Metal Ions	Amount Added (mg)	Cobalt (II) Found (g)
1	Ni (II)	30	90.3
		90	90.6
2	Cu(II)	40	90.2
		120	91.8
3	Zn (II)	70	91.4
		180	90.7
4	Mn(II)	40	89.3
		80	89.9
5	Fe (III)	80	90.8
		200	90.1
6	Ti (IV)	100	91.2
		150	90.6
7	V(V)	70	89.3
		140	89.8
8	Mo (VI)	50	88.6
		100	89.7
9	U(VI)	50	91.5
		100	90.2
Cobalt (II) : 90 µg 0.2% Reagent solution : 2.5 ml pH: 4.0 .            Polyurethane Foam : 6 Pieces

 

 

Fig No 6: Effect of Diverse Metal Ions       

 

Precision:

Ten sample solution of cobalt (II) complex with 1-benzoyl-3-(2-pyrimidyl) thiourea in 10 ml chloroform containing 90 µg of cobalt (II)  gave a mean absorbance of 0.586 with a standard deviation of 0.46%

 

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Received on 15.06.2019                    Modified on 05.07.2019

Accepted on 30.07.2019                   ©AJRC All right reserved