Development of an reliable analytical method for synergistic extractive spectrophotometric determination of cobalt(II) from alloys and nano composite samples by using chromogenic chelating ligand

Article abstract of DOI:10.1016/j.saa.2011.09.015

A synergistic simple and selective spectrophotometric method was developed for the determination of cobalt(II) with 1-(2′,4′-dinitro aminophenyl)-4,4,6-trimethyl-1,4-dihydropyrimidine-2-thiol [2′,4′- dinitro APTPT] as a chromogenic reagent. The proposed method has been described on the basis of synergistic effective extraction of cobalt(II) in presence of pyridine at pH range 9.5-10.2, showed orange-red coloured ternary complex having molar ratio 1:2:2 (M:L:Py). The equilibrium time is 10 min for extraction of cobalt(III) from organic phase. The absorbance of coloured organic layer in chloroform is measured spectrophotometrically at 490 nm against reagent blank. The Beer's law was obeyed in the concentration range 2.5-15 μg mL ^-1 of cobalt(II) and optimum concentration range was 5-12.5 μg mL^-1 of cobalt(II) and it was evaluated from Ringbom's plot. The molar absorptivity and Sandell's sensitivity of cobalt(II)-2′,4′- dinitro APTPT-pyridine complex in chloroform are 1.109 × 10³ L mol^-1 cm^-1 and 0.053 μg cm^-2, respectively while molar absorptivity and Sandell's sensitivity of cobalt(II)-2′, 4′-dinitro APTPT complex in chloroform are 6.22 × 10² L mol^-1 cm^-1 and 0.096 μg cm^-2, respectively. The composition of cobalt(II)-2′,4′-dinitro APTPT-pyridine complex (1:2:2) was established by slope ratio method, mole ratio method and Job's method of continuous variation. The ternary complex was stable for more than 48 h. The interfering effects of various cations and anions were also studied, and use of suitable masking agents enhances the selectivity of the method. The method is successfully applied for the determination of cobalt(II) in binary, synthetic mixtures and real samples. A repetition of the method was checked by finding relative standard deviation (R.S.D.) for n = 5 which was 0.15%. The reliability of the method is confirmed by comparison of experimental results with atomic absorption spectrophotometer.

Full text of DOI:10.1016/j.saa.2011.09.015

Spectrochimica Acta Part A 84 (2011) 117–124
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Development of an reliable analytical method for synergistic extractive
spectrophotometric determination of cobalt(II) from alloys and nano composite
samples by using chromogenic chelating ligand
Ganesh S. Kamblea, Anita A. Gharea, Sanjay S. Kolekara, Sung H. Hanb, Mansing A. Anusea,∗
a Analytical Chemistry Laboratory, Department of Chemistry, Shivaji University, Kolhapur 416004, Maharashtra, India
b Inorganic Nano-Material Laboratory, Department of Chemistry, Hanyang University, Seoul 133-791, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 July 2011
Received in revised form 7 September 2011
Accepted 9 September 2011
A synergistic simple and selective spectrophotometric method was developed for the determination
of cobalt(II) with 1-(2ꢀ,4ꢀ-dinitro aminophenyl)-4,4,6-trimethyl-1,4-dihydropyrimidine-2-thiol [2ꢀ,4ꢀ-
dinitro APTPT] as a chromogenic reagent. The proposed method has been described on the basis of
synergistic effective extraction of cobalt(II) in presence of pyridine at pH range 9.5–10.2, showed orange-
red coloured ternary complex having molar ratio 1:2:2 (M:L:Py). The equilibrium time is 10 min for
extraction of cobalt(III) from organic phase. The absorbance of coloured organic layer in chloroform is
measured spectrophotometrically at 490 nm against reagent blank. The Beer’s law was obeyed in the
concentration range 2.5–15 ␮g mL−1 of cobalt(II) and optimum concentration range was 5–12.5 ␮g mL−1
of cobalt(II) and it was evaluated from Ringbom’s plot. The molar absorptivity and Sandell’s sensitiv-
ity of cobalt(II)-2ꢀ,4ꢀ-dinitro APTPT-pyridine complex in chloroform are 1.109 × 103 L mol−1 cm−1 and
0.053 ␮g cm−2, respectively while molar absorptivity and Sandell’s sensitivity of cobalt(II)-2ꢀ,4ꢀ-dinitro
APTPT complex in chloroform are 6.22 × 102 L mol−1 cm−1 and 0.096 ␮g cm−2, respectively. The compo-
sition of cobalt(II)-2ꢀ,4ꢀ-dinitro APTPT-pyridine complex (1:2:2) was established by slope ratio method,
mole ratio method and Job’s method of continuous variation. The ternary complex was stable for more
than 48 h. The interfering effects of various cations and anions were also studied, and use of suitable
masking agents enhances the selectivity of the method. The method is successfully applied for the deter-
mination of cobalt(II) in binary, synthetic mixtures and real samples. A repetition of the method was
checked by finding relative standard deviation (R.S.D.) for n = 5 which was 0.15%. The reliability of the
method is confirmed by comparison of experimental results with atomic absorption spectrophotometer.
Keywords:
Cobalt(II)
Synergistic extraction
2ꢀ,4ꢀ-Dinitro APTPT
Pyridine
Spectrophotometry
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
ature alloys with steels. These alloys find important uses in gas
turbine engines and in high speed steels which is used to make cut-
Cobalt occurs to the extent of 23 ppm by weight in the earth
crusts. Cobalt is present in many ores at micro as well as macro
level. Cobalt(II) ores are always found together with nickel and cop-
per ores and sometimes with lead ore [1]. Mainly cobalt is used
in metallurgical industries and about 20–25% is used for chemi-
cal industries [2]. Cobalt alloys are used in some relative industrial
products because of their sufficient hardness and resistivity against
oxidation. About 1/3 of cobalt produced is used for high temper-
ting tool for lathes. High working speed can be used as these tools
retain their hardness and cutting edge even at red heat. Exception-
ally hard alloys can be made instead of diamond in rocks, drills, e.g.
Stellite (50% Co, 27% Cr, 12% W, 5% Fe, 2.5% C), and Widia metal
(tungsten carbide WC with 10% Co).
About 1/3 of cobalt produced is used to make the pigments
which are used to make blue ceramic glass and in paint indus-
tries. Cobalt is ferromagnetic like iron and nickel; 1/5 of the cobalt
produced is used to make the magnetic alloys, such as, Alinico con-
taining aluminium, nickel and cobalt. These alloys make permanent
magnetes which are 20–30 times more powerful than Fe. Cobalt is
used in cobaltoxide nano materials due to its magnetism and also
in semiconducting materials.
Abbreviations: 4ꢀ-chloro PTPT, 1-(4ꢀ-chlorophenyl)-4,4,6-trimethyl(1H,4H)-
2- pyrimidine thiol; 2ꢀ,4ꢀ-dinitro APTPT, 1-(2ꢀ,4ꢀ-dinitro aminophenyl)-4,4,6-
trimethyl-1,4- dihydropyrimidine-2-thiol; DMG, dimethylglyoxime; PAR, 4-(2-
pyridylazo) resorcinol; Py, pyridine.
Small amounts of cobalt salts of fatty acids from linseed oil
and naphthanic acid are used as dryers, to speed the drying of the
oil paints. Cobalt is an essential constitutent of fertile soil and is
∗
Corresponding author. Tel.: +91 231 2609380; fax: +91 231 2692333.
E-mail address: mansinganuse@yahoo.co.in (M.A. Anuse).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.09.015

118
G.S. Kamble et al. / Spectrochimica Acta Part A 84 (2011) 117–124
1.2
A
0.5
Reagent
With pyridine
Coloured complex
0.45
Without pyridine
1
A
0.4
0.35
0.3
B
0.8
0.6
0.4
0.2
0
0.25
0.2
B
0.15
0.1
0.05
0
0
2
4
6
8
pH
10
12
14
16
Fig. 2. Effect of pH on the extraction of, (A) Co(II)-2ꢀ,4ꢀ-dinitro APTPT-pyridine
complex, (B) Co(II)-2ꢀ,4ꢀ-dinitro APTPT complex. Co(II) = 10 ␮g mL−1; pH = 1–14;
300
350
400
450
500
550
600
2ꢀ,4ꢀ-dinitro APTPT = 5 cm3 of 0.02 mol L−1
; ; sol-
pyridine = 5 cm3 of 1.0 mol L−1
Wavelength, nm
vent = chloroform; equilibrium time = 10 min, ꢁmax = 490 nm.
Fig. 1. (A) Absorption spectra of 2ꢀ,4ꢀ-dinitro APTPT vs. chloroform blank, (B) absorp-
tion spectra of Co(II)-2ꢀ,4ꢀ-dinitro APTPT-pyridine complex vs. 2ꢀ,4ꢀ-dinitro APTPT
blank. Co(II) = 10 ␮g mL−1
; ;
pH = 9.7, 2ꢀ,4ꢀ-dinitro APTPT = 5 cm3 of 0.02 mol L−1
pyridine = 5 cm3 of 1.0 mol L−1; solvent = chloroform; equilibrium time = 10 min;
wavelength = 300–600 nm.
widely used analytical methods are those based on the spectropho-
tometric techniques due to the resulting experimental rapidity,
simplicity and wide applications [11–28] (Table 1).
present in some enzymes and vitamin B12 (cynocobalamine) which
are noted for biological activities. Artificial isotopes Co60 is radioac-
tive and undergoes ˇ decay, it gives intense high energy ꢀ radiation,
which is used in hospitals for radiotherapy of cancerous tumors.
A wide range of cobalt containing compounds finds almost in all
real samples, such samples are constant modulus alloys, magne-
tostrictive alloys, dental and prosthetic alloys, glass to metal seals,
electrical resistance, heating elements, nano composite material
samples and soft magnetic alloys.
On the other hand, cobalt is a vital trace element in animal nutri-
tion and its deficiency may lead to retarded growth, loss of appetite,
anemia and rapid recovery from these symptoms occurs upon feed-
ing them with a cobalt supplemented diet. However, cobalt can
irritate the gastro intestinal tract and can cause nausea, vomiting
and diarrhea in humans while they are not particularly toxic to
animals [3,4]. Therefore, the determination of cobalt is valuable
for the quality control of artificial and biological samples, alloys
and nano material composites in a simple, selective and sensitive
manner.
The main goal of the present report is to synthesize 1-(2ꢀ,4ꢀ-
dinitro aminophenyl)-4,4,6-trimethyl-1,4-dihydropyrimidine-2-
thiol, as a sensitive chelating agent and developing a simple
and proper method for spectrophotometric monitoring of cobalt
traces. It was experimentally observed that, 1-(2ꢀ,4ꢀ-dinitro
aminophenyl)-4,4,6-trimethyl-1,4-dihydropyrimidine-2-thiol
reacts with cobalt(II) and produces orange-red coloured complex
in presence of pyridine. This method is used for analyzing cobalt(II)
from synthetic mixtures as well as alloys and nano composite
material samples.
2. Experimental
2.1. Apparatus
Absorption spectra were obtained with an Elico digital spec-
trophotometer model Systronic 106 using 1 cm quartz cell. The
pH values were determined with an Elico digital pH meter model
LI-120.
Glass vessels were cleaned by soaking in acidified solutions of
potassium dichromate, followed by washing with soap water and
rinsed two times with water.
A literature survey reveals that, there are several techniques
and methods such as X-ray fluorescence [5], atomic fluores-
cence spectrometry [6], polarography [7], chromatography [8],
atomic absorption spectrophotometry [9], and inductively coupled
plasma-atomic emission spectrophotometry [10]. Among the most

Table 1
Comparison of the present method with other spectrophotometric methods for the determination of cobalt(II).
Reagent
ꢁmax (nm)
Acidity/pH
Beer’s law validity
range (ppm)
Molar absorptivity
M:La
Remarks
Ref. no.
(L mol−1 cm−1 ε)
2-(2-Benzo- thiazolylazo)-2-p-cresol
5-(6-Methoxy-2-benzothiazoleazo)-8-aminoquinoline
4-(5-Bromo-2-pyridylazo)-1,3-diaminobenzene
2-(2-Thiazolylazo)-4-methyl-5-(sulfo- methylamino)
benzoic acid
2-(2-Thiazolylazo)-4-methyl-5-(sulfo- methylamino)
benzoic acid
Tetrametylene-bis(triphenyl- phosphonium)
Benzyltributylammonium tetrathiocyanato-
cobaltate(II)
615
pH 6.50–7.50
0–1.60
0–0.40
0.6–25
ε = 1.62 × 104
ε = 1.15 × 105
ε = 1.16 × 105
ε = 6.0 × 104
1:3
1:2
1:2
–
Absorption Increased in presence of TritonX-100
Cobalt(II) and Ni(II) determines simultaneously
10 min waiting for maximum colour absorbance
Interference ions are masked by EDTA
[11]
[12]
[13]
[14]
pH 9.4–10.0
2.4 M HCl
pH 5.0
655
573
655
–
pH 5.0–6.0
655
0–13
ε = 1.13 × 105 s = 0.52
1:2
Successfully determined cobalt(II) from reagent
grade Ni-salt and glass
Equilibrium time 30 s
[15]
pH 6.5
pH 7.0
625
625
0–130
0–120
ε = 1.5 × 104
ε = 1327
1:1
1:1
[16]
[17]
Method is sensitive
2-Hydroxy-3-methoxy benzaldehyde
thiosemicarbazone
pH 6.0
468.5
540
0.059–3.299
0–7
–
–
–
Simultaneous determination of cobalt(II) and
Ni(II)
[18]
[19]
4,4ꢀ-Diazobenzene- diazoaaminobenzobenzene
pH 10.2
ε = 1.72 × 105 s = 0.00035
Triton X-114 was used as a surfactant and
complex was stable for 24 h
Triton X-100 was used as a surfactant
SDS was used as a surfactant
Equilibrium time 1.5 min
1-Nitroso-2-naphthol
pH 4.0
pH 1.0
425
550
390
430
458
473
535, 555
0.05–2.5
0–25
0.05–1.3
0–19
0.1–15
0.01–8.0
–
ε = 4.62 × 104
–
[20]
[21]
[22]
[23]
[24]
[25]
[26]
2-(2-Pyridylazo)-5-ethylaminophenol
Benzeneacetaldehyde-4-hydroxy-␣-oxo-aldoxime
3-Hydroxy-2-methyl-1,4-naphthoquinone 4-oxime
Bis(salicylaldehyde) orthophenylene- diamine
Bis(5-bromosalicyl- aldehyde)orthophenylenediamine
5-[3-(1,2,4-Triazolyl-azo)]-2,4-dihydroxy-
benzaldehyde
ε = 5.5 × 104
1:1
1:3
–
1:1
1:1
1:1
pH 8.6–9.4
pH 6.0
0.005 M H2SO4
pH 3.4–4.0
pH 8.0
ε = 2.746 × 104
ε = 2.09 × 104
Extarction carried out 60 ◦
C
Coloured complex stable for 24 h
Highly sensitive
ε = 1.109 × 104 s = 6.0
ε = 5.84 × 104 s = 9.0
ε = 2.0456 × 104 s = 2.881 × 10−3
Coloured complex stable for 24 h
Isonitroso-5-methyl-2-hexanone
pH 8.8
pH 4.0
pH 9.7
400
630
690
0.1–5.0
0.01–0.32
2.5–15
ε = 1.135 × 104 s = 5.176
ε = 1.4 × 105
1:3
1:2
1:2
Equilibrium time 20 s
CTMAB was used as a surfactant
Selective and reproducible
[27]
[28]
P.M.b
2-(2-Quinolinylazo)-5-diethylamino- benzoic acid
2ꢀ,4ꢀ-Dinitro APTPT
ε = 2.843 × 103 s = 0.053
a
Metal:ligand.
Present method.
b

120
G.S. Kamble et al. / Spectrochimica Acta Part A 84 (2011) 117–124
Table 2
2.2. Standard cobalt(II) solution
Spectral characteristics and precision data of cobalt(II)-2ꢀ,4ꢀ-dinitro APTPT-pyridine
complex.
A stock solution of cobalt (1 mg mL−1) was prepared by dis-
solving an accurately weighed amount of cobaltous oxide (4.085 g,
Merck) in 1000 mL of water with a few drops of concentrated
hydrochloric acid and standardized by a known method [29].
Optical characteristics and precision
Parameters
Solvent
ꢁmax (nm)
pH range
Chloroform
490
9.5–10.2 (9.7)
2ꢀ,4ꢀ-Dinitro APTPT concentration
Pyridine concentration
Equilibrium time (min)
Stability (h)
5 mL (0.02 mol L−1
)
2.3. 1-(2ꢀ,4ꢀ-Dinitro
5 mL (1.0 mol L−1
10
>48
2.5–15
5–12.5
)
aminophenyl)-4,4,6-trimethyl-1,4-dihydropyrimidine-2-thiol
solution
Beer’s law range (␮g mL−1
)
Ringbom optimum conc. range (␮g mL−1
)
1-(2ꢀ,4ꢀ-Dinitro
aminophenyl)-4,4,6-trimethyl-1,4-
With pyridine
dihydropyrimidine-2-thiol, [2ꢀ,4ꢀ- dinitro APTPT] was synthesized
and recrystallised as reported by Mathes [30]. A 0.02 M stock
solution was prepared by dissolving 0.324 g of 2ꢀ,4ꢀ-dinitro APTPT
in a 50 cm3 of chloroform.
Molar absorptivity (L mol−1 cm−1
)
)
2.843 × 103
Sandell’s sensitivity (␮g cm−2
)
0.023
Without pyridine
Molar absorptivity (L mol−1 cm−1
6.22 × 102
0.096
Sandell’s sensitivity (␮g cm−2
)
Relative standard deviationa, (%)
Range of error
0.15
0.2
2.4. Solutions of foreign ions
Mean recovery
Stoichiometry of the extracted complex
99.9 0.06
1:2:2 (M:L:Y)
Other standard solutions of different metals used to study the
effect of foreign ions were prepared by dissolving weighed quan-
tities of their salts in water or dil. HCl. Solutions of anions were
prepared by dissolving the respective alkaline metal salts in water.
Different synthetic mixtures containing cobalt(II) were prepared by
combining with commonly associated metal ions in definite com-
position. All of the chemicals used were of AR grade. Double distilled
water was used throughout the work.
a
Average of five determinations.
3.2. Effect of pH
The effect of pH on the formation of the cobalt(II)-2ꢀ,4ꢀ-dinitro
APTPT-pyridine complex was investigated by varying the pH of
cobalt(II) solution in the range from 1 to 14 before the addition
of the organic phase. The result in Fig. 2 showed that the optimal
pH for the reaction of cobalt(II) with 2ꢀ,4ꢀ-dinitro APTPT is 9.5–10.2
in the presence and absence of pyridine. However, in the pres-
ence of 5.0 mL of 0.5 mol L−1 pyridine, there was enhancement of
absorbance but in absence of pyridine absorbance was decreased
in the same pH range. Thus, pyridine showed a synergistic effect
on the extraction of cobalt(II) with 2ꢀ,4ꢀ-dinitro APTPT complex. On
the other hand, further increase in the pH caused a sharp decrease
in the percentage extraction may due to hydrolysis of the complex.
Hence, pH 9.7 was recommended for further studies.
2.5. Recommended procedure
An aliquot of the sample solution containing 100 ␮g cobalt(II)
solution was taken in 25.0 mL of calibrated flask and pH was
adjusted to 9.7 with dilute hydrochloric acid and sodium hydroxide.
The solution was transferred into a 125 mL separatory funnel and
thoroughly mixed with 5.0 mL of a 0.02 mol L−1 2ꢀ,4ꢀ-dinitro APTPT
and 5.0 mL of 0.5 mol L−1 pyridine in chloroform and made the total
volume of organic phase to 10.0 mL by addition of 3.0 mL of chloro-
form and equilibrated for 10 min. The two phases were allowed to
separate and dried over anhydrous sodium sulphate. The organic
layer having an orange-red colour was transferred to a 10.0 mL of
standard volumetric flask and made upto the mark with chloro-
form. The absorbance of the coloured complex was measured at
490 nm against reagent blank prepared in similar manner. Percent-
age extraction (%E) and metal distribution ratio (D) were calculated
according to Eqs. (1) and (2), respectively.
3.3. Effect of solvent
Various organic solvents were examined for the extrac-
tion of cobalt(II) with 2ꢀ,4ꢀ-dinitro APTPT complex in presence
of 5 mL of 0.5 mol L−1 pyridine. It was observed that, the
percentage extraction (%E) values increased in the order of
kerosene (4.3), <n-butanol (15.5) < amyl alcohol (23.8) < amyl
acetate (36.5) < toluene (40.1) < xylene (54.3) < methyl-iso-butyl
ketone (59.1) < 1,2-dichloroethane (73.1) < carbon tetrachloride
(88.1) < chloroform (99.9). Among these, chloroform was used for
further extraction.
[M]org.
%E =
D =
× 100
(1)
(2)
[M]aq., init.
[M]org.
[M]aq.
where [M]aq.,init. represents the initial concentration of metal ion in
the aqueous phase. [M]aq. and [M]org. are the total concentrations
of metal ion in the aqueous and organic phases after equilibrium,
respectively.
3.4. Effect of 2ꢀ,4ꢀ-dinitro APTPT concentration
3. Results and discussion
The concentration of 2ꢀ,4ꢀ-dinitro APTPT in chloroform was
varied from 0.001 to 0.01 mol L−1 for full colour development in
presence of 5.0 mL of 0.5 mol L−1 pyridine at pH 9.5. In absence
of pyridine, absorbance was lowered. Therefore, the extraction
of cobalt(II) was complete and reproducible with 0.007 mol L−1
2ꢀ,4ꢀ-dinitro APTPT in presence of pyridine. However, 5 mL of
0.02 mol L−1 reagent was recommended in order to ensure the
complete complexation. There was no significant change in the
absorption with excess of the reagent concentration.
3.1. Absorption spectra and spectral characteristics of coloured
complex
A orange-red colour complex formed with 2ꢀ,4ꢀ-dinitro APTPT
in presence of pyridine as an auxiliary ligand in chloroform have
shown the maximum absorbance at 490 nm. The spectra of the
reagent and coloured complex are shown in Fig. 1. And the spectral
characteristics are given in Table 2.

G.S. Kamble et al. / Spectrochimica Acta Part A 84 (2011) 117–124
121
0
10
20
30
40
50
60
70
80
90
2
pH = 9.0
pH = 10.5
With pyridine
1.5
1
Slope = 1.80
Slope = 1.83
0.5
0
-0.5
-1
-1.5
-2
0.9
1.1
1.3
1.5
1.7
1.9
2.1
2.3
2.5
Log ppm, Co(II)
Fig. 3. Ringbom’s plot for determination optimum cobalt(II) concentration.
Co(II) = 25–225 ␮g; pH = 9.7; 2ꢀ,4ꢀ-dinitro APTPT = 5 cm3 of 0.02 mol L−1
;
Pyri-
-7
-6
-5
-4
-3
-2
-1
dine = 5 cm3 of 1.0 mol L−1
; solvent = chloroform; equilibrium time = 10 min,
Log C[2’,4’-dinitro APTPT]
ꢁmax = 490 nm.
Fig.
4. Slope
ratio
method:
with
fixed
pyridine
concentration:
ꢀ
ꢀ
Log D[Co(II)] − Log C[2 ,4 -dinitro APTPT] plot for determination of composition of
extracted species in chloroform, Co(II) = 10 ␮g mL−1 pH = 9.0 and 10.5; 2ꢀ,4ꢀ-
Dinitro APTPT = 0.1–3.5 cm3 of 0.02 mol L−1 Pyridine = 5 cm3 of 1.0 mol L−1
3.5. Effect of shaking time
;
;
;
solvent = chloroform; equilibrium time = 10 min, ꢁmax = 490 nm.
The optimum shaking time of 7 min was determined by varying
the shaking time from 0.5 to 20 min in absence and presence of
pyridine. Prolonged shaking has no adverse effect on the extraction
of cobalt(II) in presence of pyridine. Hence, a shaking time of 10 min
was selected for subsequent experiment.
3.8. Beer’s law and sensitivity
The system obeyed Beer’s law over the concentration
range 2.5–12.5 ␮g mL−1 of cobalt(II) and optimum concentra-
tion range is 5–10 ␮g mL−1
, which is shown in Fig. 3 by
3.6. Effect of concentration of pyridine
Ringbom’s plot method [31]. The sensitivity of the method
defined by Sandell is 0.023 ␮g cm−2 and molar absorptivity
was 2.843 × 103 dm3 mol−1 cm−1 in presence of pyridine while
in absence of pyridine sensitivity and molar absorptivity is
0.096 ␮g cm−2 and 6.22 × 102 dm3 mol−1 cm−1, respectively. The
standard deviation calculated from ten determinations in a solution
containing 10 ␮g mL−1 of cobalt(II) is 0.02 and relative standard
deviation of the method is 0.15%.
The effect of pyridine concentration was studied from 0 to 5.0 mL
of 0.5 mol L−1 and 3.0–5.0 mL of 1.0 mol L−1 to obtain the maxi-
mum and constant colour development. It was observed that colour
of cobalt(II) complex into organic phase increases with the pyri-
dine concentration and remains constant from 3.0 mL of 1.0 mol L−1
pyridine. Therefore 5.0 mL of 1.0 mol L−1 pyridine was used for fur-
ther extraction.
3.9. Precision, accuracy of the method
3.7. Effect of colour stability of complex
The precision of the proposed method was ascertained from the
absorbance values of the actual determinations of five replicates of
fixed amounts of the cobalt(II) samples. To determine the accuracy
of the proposed method; different amount of samples containing
cobalt(II) were taken within the optimum Beer’s range limits and
analyzed by the recommended procedure. The percentage relative
standard deviation was calculated by the proposed method. The
results are summarized in Table 2.
The colour stability was studied at room temperature by mea-
suring the absorbance at regular time intervals. The absorbance of
the cobalt(II)-2ꢀ,4ꢀ-dinitro APTPT-pyridine complex in chloroform
was stable for more than 48 h. But in absence of pyridine, com-
plex was stable for 9 h. This study indicates that pyridine showed
synergistic effect on the extraction of cobalt(II). Hence, the time
of measurement of absorbance of complex in presence of pyridine
was not critical.

122
G.S. Kamble et al. / Spectrochimica Acta Part A 84 (2011) 117–124
0.16
1
0.5
0
With pyridine
Without pyridine
pH = 9.0
Slope = 1.92
Slope = 1.86
pH = 10.5
0.14
0.12
0.1
-0.5
0.08
0.06
0.04
-1
-1.5
-2.5
-2
-1.5
-1
-0.5
0
0
0.5
1
1.5
2
Log C[Pyridine]
M / L
Fig. 5. Slope ratio method: With fixed 2ꢀ,4ꢀ-dinitro APTPT concentration:
Log D[Co(II)] − Log C[Pyirdine] plot for determination of composition of extracted species
in chloroform, Co(II) = 10 ␮g mL−1; pH = 9.0 and 10.5; 2ꢀ,4ꢀ-dinitro APTPT = 5 cm3 of
0.02 mol L−1; pyridine = 0.1–3.5 cm3 of 1.0 mol L−1; solvent = chloroform; equilib-
rium time = 10 min; ꢁmax = 490 nm.
Fig. 6. Mole ratio method for determination of composition of complex. Co(II)-
2ꢀ,4ꢀ-dinitro APTPT-pyridine complex; Co(II) = 0.2–1.8 mL of 30 ␮g mL−1; pH = 9.7;
2ꢀ,4ꢀ-dinitro APTPT = 1.0 cm3 of 5.090 × 10−3 mol L−1
; equilibrium time = 10 min;
pyridine = 5.0 cm3 of 5.090 × 10−3 mol L−1; solvent = chloroform; ꢁmax = 490 nm.
3.11. Effect of diverse ions
3.10. Stoichiometry of the complex
The selectivity of the method was investigated by the determi-
nation of 100 ␮g of cobalt(II) in the presence of number of cations
and anions within a relative error of 2%. The tolerance limits for
cations and anions are summarized in Table 3. The interference of
cations was removed by using suitable masking agents, therefore
method becomes more selective.
The composition of extracted species was ascertained by slope
ꢀ
ꢀ
ratio method in which graph of log D[Co(II)] against log C[2 ,4 -dinitro
at fixed 0.5 mol L−1 pyridine concentration is plotted. The
APTPT]
plots were linear having the slopes 1.80 and 1.83 at pH 9.0 and 10.5,
respectively (Fig. 4). Also plots of log D[Co(II)] against log C[pyridine]
at fixed 0.02 mol L−1 2ꢀ,4ꢀ-dinitro APTPT concentration were linear
with slopes of 1.9 and 1.8 at pH 9.0 and 10.5, respectively (Fig. 5).
Hence, probable composition of extracted species was calculated
to be 1:2:2 (Metal:Thiol:Pyridine). The composition of extracted
species was also confirmed by Mole ratio [32] (Fig. 6) and Job’s
method of continuous variation [33].
N
S
N
The reactions of cobalt(II) with the reagent and pyridine may
therefore be represented as follows by the Eqs. (3) and (4).
Co/2
N
.2Py
H
O2N
[Co(H2O)6]2+ + 2R–SH ꢀ [Co(S-R)2(H2O)2] + 2H+ + 4H2O
[Co(S-R)2(H2O)2] + 2Py ꢁ [Co(S-R)2(Py)2]adduct + 2H2O
(3)
(4)
NO2
Based on the above reactions the probable structure is recom-
mended for the complex as shown in Fig. 7.
Fig. 7. Structure of Co(II)-2ꢀ,4ꢀ-dinitro APTPT-pyridine complex.

G.S. Kamble et al. / Spectrochimica Acta Part A 84 (2011) 117–124
123
Table 3
Table 5
Effect of diverse ions for the determination of 10 ␮g mL−1 cobalt(II) with 2ꢀ,4ꢀ-dinitro
Determination of cobalt(II) in a synthetic mixtures.
APTPT at 490 nm (relative error 2%).
Composition, ␮g
Average %
R.S.D. (%)
Amount
Foreign ions
recoverya
tolerated, Mg
Co, 100; Au, 100; Ag, 50
Co, 100; Cub,300; Au, 100
Co, 100; Ag, 50; Cub, 300
Co, 100; Nic, 100; Cub,300
Co, 100; Fe, 100; Mn, 100
Co, 100; Nib, 100; Pd, 100
Co, 100; Fe, 100; Ru, 100
Co, 100; Pd, 100; Au, 100
Co, 100; Zn, 100; Cdc, 300
Co, 100; Hgb, 100; Ag, 50
99.9
99.8
99.8
99.8
99.8
99.9
99.5
99.8
99.8
99.9
0.14
0.18
0.15
0.17
0.20
0.14
0.50
0.21
0.20
0.10
25
Pb(II), Sn(II), Al(III), Mg(II), Ca(II), Ta(V),
Thiocyanate, Phosphate, Salicyalate
Mn(II), Zn(II), Ga(III), Tl(I), Sr(II), Mo(VI)
Cr(III), Se(IV), Te(IV), Pd(II)a, Hg(II)a, Citrate,
Acetate, EDTA
15
10
5
3
Cr(VI), Bi(III), In(III), Ba(III), Pt(IV), Ni(II)b, Sulphate,
Fluoride, Nitrate, Thiosulphate
Fe(III), Sb(III), Cu(II)a, Cd(II)b, Iodide, Bromide,
Nitrite, Thiourea
1
Ag(I)a, Fe(II), Au(III)
Nb(V), Zr(IV)
U(VI)
Th(IV), Gd(III)
a
Average of five determinations.
0.5
0.3
0.1
b
Masked with 5 mg I−
.
c
Masked with 10 mg EDTA.
a
Masked with 3 mg of I−
Masked with 10 mg EDTA.
.
Table 6
Determination of cobalt(II) from cobalt oxide nano powder and alloy.
b
Cobalt oxide nano
materials/alloy
Amount of Co(II)
founda mg/gm
Confidence
limit ˛ = 0.95
R.S.D. (%)
4. Applications
Proposed
method
AAS
method
4.1. Separation of cobalt(II) from associated metal ions
b
CeCoO3
48.77
32.12
29.08
48.79
32.11
29.09
1.41
1.21
2.26
1.16
0.006
0.016
0.011
0.013
The method was successfully applied for the separation and
determination of cobalt(II) from associated metal ions containing
Au(III), Sb(III), Cu(II), Pd(II), Fe(III), Ru(III), Ni(II) and Mn(II).
Cobalt(II) separated from Au(III), Sb(III), Fe(III), Ru(III), and
Mn(II) by optimized recommended procedure. Under optimized
conditions, added metal ions remained quantitatively in the aque-
ous phase, which was evaporated to moist dryness by treating with
5.0 mL concentrated hydrochloric acid. The residue was dissolved
in water and diluted to appropriate volume. The added metal ions
were determined by standard methods [34–36].
b
ZnCoFe2O4
ZnCoFeDyO4
b
Nickel-Base alloy
105.01
105.02
(387 BCS)c
Nickel-Base alloy (387 BCS): Co, 0.21%; Cr, 12.46%; Ti, 2.95%; Al, 0.24%; C, 0.30%; Mo,
5.83%; B, 0.016%; Mn, 0.08%; Si, 0.28%; Fe, 36.0%; Ni, 41.9%; Cu, 0.032%.
a
Average of five determinations.
Cobalt nano powder, Department of Chemistry, Shivaji University, Kolhapur,
b
India.
c
Alloy, Department of Chemistry, Shivaji University, Kolhapur, India.
Copper(II), Ni(II), and Pd(II) were co-extracted under the opti-
mum extraction condition of cobalt(II), therefore, separation of
cobalt(II) from these metal ions can be achieved by using I−
for Cu(II) and EDTA for Ni(II) and Pd(II) as a masking agent.
The added metal ions remained in aqueous phase were subse-
quently demasked by treating with 5.0 mL concentrated nitric
acid and determined by reported methods [35,37,38] (Table 4).
While extracted cobalt(II)-2ꢀ,4ꢀ-dinitro APTPT-pyridine complex
estimated spectrophotometrically at 490 nm against reagent blank.
4.2. Determination of cobalt(II) from synthetic mixtures
Several synthetic mixtures of varying compositions containing
100 ␮g of cobalt(II) and associated metal ions of known concentra-
tion were added, followed by respective masking agents. Extraction
of cobalt(II) was analyzed by employing the recommended pro-
cedure (Table 5). The results obtained were in perfect and good
agreement with the amount added.
Table 4
Separation of cobalt(II) from associated metal ions.
Metal ion
Amount
taken
(␮g)
Average %
recoverya
R.S.D. %
Chromogenic
ligand
Ref. no.
4.3. Analysis of cobalt(II) from cobaltoxide nano powder and alloy
Co(II)
Au(III)
100
100
99.8
99.9
0.08
0.09
2ꢀ,4ꢀ-dinitro [34]
APTPT
The proposed method has been successfully applied for the
determination of cobalt(II) from cobalt oxide nano powder and
alloy (Table 6). These samples were boiled with 10.0 mL aqua-regia,
evaporated to moist dryness by gentle heating on hot plate. The
solution was boiled with hot water and filtered through Whatmann
filter paper No. 1. The residue was evaporated to moist dryness
by the addition of 2 mL × 5 mL portion of conc. HCl. The filtrate
was diluted to required volume with water. An aliquot of cobalt(II)
solution was analyzed by the recommended procedure. The results
were found to be in good agreement with those obtained by AAS.
Co(II)
Sb(III)
100
250
99.9
98.7
0.09
1.32
Ascorbic
acid + KI
[35]
Co(II)
100
300
99.9
99.8
0.21
0.09
Cu(II)b
2ꢀ,4ꢀ-Dinitro [37]
APTPT
Co(II)
Pd(II)
100
100
99.9
99.7
0.13
0.09
4ꢀ-Chloro
PTPT
[38]
Co(II)
Fe(III)
Co(II)
Ru(III)
Co(II)
Ni(II)c
Co(II)
Mn(II)
100
100
100
200
100
75
99.9
98.8
99.9
99.7
99.9
98.4
99.9
99.9
0.09
0.08
0.09
0.18
0.09
1.51
0.09
0.13
Thiocyanate [35]
Thiourea
DMG
[36]
[35]
[35]
5. Conclusion
The newly synthesized 2ꢀ,4ꢀ-dinitro APTPT has been proved
to be a selective reagent for cobalt(II) when compared to other
spectrophotometric methods. It is successfully applied to the deter-
mination of cobalt(II) in synthetic mixtures, nano powder and
alloys.
100
100
PAR
a
Average of five determinations.
b
c
Masked with 3 mg I−
Masked with 10 mg EDTA.
.

124
G.S. Kamble et al. / Spectrochimica Acta Part A 84 (2011) 117–124
Salient features:
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One of the authors Ganesh S. Kamble is highly grateful to
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Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2011.09.015.