Journal of Hazardous Materials 147 (2007) 15–20
Preconcentration and solid phase extraction method for the
determination of Co, Cu, Ni, Zn and Cd in environmental
and biological samples using activated carbon by FAAS
a
D
K. Kiran a , K. Suresh Kumar b , K. Suvardhan b , K. Janardhanam a,∗ , P. Chiranjeevi b
Department of Environmental Sciences, S. V. University, Tirupati 517502, AP, India
b Department of Chemistry, S. V. University, Tirupati 517502, AP, India
TE
Received 4 May 2006; received in revised form 2 August 2006; accepted 18 December 2006
Available online 21 December 2006
Abstract
AC
2-{[1-(2-Hydroxynaphthyl) methylidene] amino} benzoic acid (HNMABA) was synthesized for solid phase extraction (SPE) to the determination
of Co, Cu, Ni, Zn and Cd in environmental and biological samples by flame atomic absorption spectrophotometry (FAAS). These metals were
sorbed as HNMABA complexes on activated carbon (AC) at the pH range of 5.0 ± 0.2 and eluted with 6 ml of 1 M HNO3 in acetone. The effects
of sample volume, eluent volume and recovery have been investigated to enhance the sensitivity and selectivity of proposed method. The effect of
interferences on the sorption of metal ions was studied. The concentration of the metal ions detected after preconcentration was in agreement with
the added amount. The detection limits for the metals studied were in the range of 0.75–3.82 g ml−1 . The proposed system produced satisfactory
results for the determination of Co, Cu, Ni, Zn and Cd metals in environmental and biological samples.
© 2007 Elsevier B.V. All rights reserved.
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1. Introduction
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Keywords: 2-{[1-(2-Hydroxynaphthyl) methylidene] amino} benzoic acid (HNMABA); Solid phase extraction; Activated carbon; Environmental and biological
samples; Flame atomic absorption spectrometry
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Nowadays determination of trace metals in environmental
samples is essential, because of these metals have been used
in various industries. Various techniques have been reported
for the determination of trace metals in environmental samples. Flame atomic absorption spectrometry (FAAS) has been
widely used for the determination of trace metal ions. However, direct determination of metal ions at trace levels by
FAAS is limited due to their low concentrations and matrix
interferences [1]. In trace analysis, therefore, preconcentration
leads to simplified trace metal determination. Several methods
of preconcentration include solvent extraction [2,3], adsorption [4,5], membrane extraction [6], coprecipitation [7–9],
ion-exchange [10,11]. But, solid phase extraction (SPE) is
multielement preconcentration methods because of its sim-
∗
Corresponding author. Tel.: +91 877 2276622; fax: +91 877 2261274.
E-mail address: kandukurijanardhanam@gmail.com (K. Janardhanam).
0304-3894/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jhazmat.2006.12.044
plicity, rapidity and ability to attain a high concentration
factor.
Activated carbon has been widely used for many purposes due
to its ability [12–17], to adsorb organic compounds and organic
metal complexes. Enrichment of trace metals using activated
carbon has been carried out with very high preconcentration
factors in different matrices [18–28]. The standard method for
determination of trace metals in environmental samples involves
the use of ammonium pyrrolidine dithiocarbamate for complex
formation, followed by extraction of the metal complex with
methyl isobutyl ketone (MIBK) [29] and subsequent determined
by flame atomic absorption spectrometry. The disadvantages
of above reported techniques are the large amount of solvent
required and time consuming.
Hence, there is a need to develop simple, sensitive reagent
that requires less solvent preconcentration method for the determination of metal ions in various environmental matrices. In the
present study, 2-{[1-(2-hydroxynaphthyl) methylidene] amino}
benzoic acid (HNMABA) was synthesized and impregnated
onto activated carbon for the preconcentration of Co, Cu, Ni,
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K. Kiran et al. / Journal of Hazardous Materials 147 (2007) 15–20
Zn and Cd in environmental and biological samples. The metals
determination was performed by FAAS.
2. Experimental
2.1. Apparatus
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Flame Atomic Absorption Spectrometer (Perkin-Elmer
Model AAnalytst100) was used to determine metal concentrations using an air/acetylene flame. The instrumental parameters
were those recommended by the manufacturer were represented
in Table 1. The SPE was performed using 25 ml polyethylene
tubes and frits. A digital pH meter (Elicho Li 129 model) was
used for all pH measurements.
2.4. Metals preconcentration procedure
2.4.1. Batch method
An aliquot of 100 ml of sample solution containing
0.1 g ml−1 of each metals Co(II), Cu(II), Ni(II), Zn(II) and
Cd(II) was taken in a 250 ml glass stoppered bottle. Before taking
these aliquots pH was previously adjusted to a value. Then 0.1 g
of activated carbon impregnated with HNMABA was added to
the bottle and the mixture was shaken for 30 min. After filtration,
the substrate was eluted with 6.0 ml of 1 M HNO3 in acetone.
The concentration of metal ion in the eluate was determined by
FAAS.
AC
All reagents and solvents were standard analytical grade and
used without further purification. Double distilled water has been
used for all reagents preparation. Working standard solutions of
Co, Cu, Ni, Zn and Cd (Merck Chemicals, Mumbai, India) were
prepared by stepwise dilution of 1.0 g ml−1 . Sodium acetate
buffer solution was prepared by adding an appropriate amount of
acetic acid to sodium acetate solution until pH 5.0 was attained.
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Scheme 1. Synthesis of 2-{[1-(2-hydroxynaphthyl) methylidene] amino} benzoic acid.
2.2. Reagents
2.3. Synthesis of 2-{[1-(2-hydroxynaphthyl) methylidene]
amino} benzoic acid
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2-Hydroxy1-naphthaldehyde (0.138 g, 1 mmol) and
anthranilic acid (0.137 g, 1 mmol) were dissolved in dry diethyl
ether and the mixture was stirred at room temperature for 3 h. The
solvent was removed on a rotary evaporator to get red colored
Schiff’s base HNMABA, which was recrystallized in ethanol.
Scheme of the reagent preparation was shown in Scheme 1.
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Table 1
Instrumental conditions for the determination of cobalt, copper, nickel, zinc and
cadmium with HNMABA impregnated on activated carbon using SPE
2.0
15
Hollow cathode lamp
Lamp current
Slit width
Burner height
Homonature photonics L 233 lamp
12 mA
0.5 nm
7 mm
Wave length (nm)
Cobalt
Copper
Nickel
Zinc
Cadmium
240.7
324.8
232.0
213.9
228.8
Measurement mode
Background correction
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Flame: acetylene–air (l min−1 )
Acetylene
Air
Detection limits
Cobalt
Copper
Nickel
Zinc
Cadmium
(g ml−1 )
1.09
0.75
1.72
1.10
3.82
2.4.2. Column method
AC loaded with 2-{[1-(2-hydroxynaphthyl) methylidene]
amino} benzoic acid (1.0 g) was packed in a glass column
(1.0 cm × 10 cm) and treated with 1 M HNO3 in acetone [30]
washed with double distilled water until the AC was free
from acid. A suitable aliquot of the solution containing Co(II),
Cu(II), Ni(II), Zn(II) and Cd(II) was passed through the column, after adjusting its pH to an optimum value at a flow rate of
0.5–3.0 ml min−1 . The column was washed with double distilled
water in order to remove free metal ions. The eluate of the metal
ions from the AC was carried out by 1 M HNO3 in acetone. The
eluate was collected in 25 ml calibrated flask and made up to the
mark with double distilled water. Finally, this aliquot was aspirated into the nebulizer of FAAS for the determination of Co(II),
Cu(II), Ni(II), Zn(II) and Cd(II) in various environmental and
biological samples.
2.4.3. Determination of metal ions in water samples
The optimized preconcentration method (AC-HNMABA)
was used applied to preconcentrate Co(II), Cu(II), Ni(II), Zn(II)
and Cd(II) ions in water samples collected from the industrial
areas (Gajulamanyam) and Gram Panchayaty taps (Chandragiri), followed by their determination with by FAAS. The
estimation of all these metal ions concentration was made with
and without (referred as direct determination) standard addition (S.A.) by passing 1000 ml of water sample (spiked with
50–100 g of each of the five metal ions in the case of standard
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K. Kiran et al. / Journal of Hazardous Materials 147 (2007) 15–20
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addition method) through the column packed with 1.0 g of matrix
after adjusting the pH to an optimum value and determining the
metal ion as described in the recommended column procedure.
The elution was made with 1 M HNO3 in acetone was used. The
results obtained are given in Table 6 and reflect the suitability
of the preconcentration column method using AC-HNMABA
for water analysis. The concentrations reported in Table 6 as
estimated by standard addition method are the values obtained
by subtracting the amount of metal added for spiking from the
total metal recovered. The closeness of results of direct and standard addition method indicates the reliability of present results
of good agreement were obtained between the direct and standard addition methods indicating the reliability of the proposed
method for metal analysis in water samples.
Fig. 1. Effect of pH.
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by adding 100 g of each of element individually in 150 ml
doubly distilled water and determined by complexing with ACHNMABA in the pH range of 2.0–7.0 as shown in Fig. 1. The
results indicate maximum recovery was obtained at pH 5.0 ± 0.2
for all the elements. So, pH 5.0 ± 0.2 was selected as further
investigation.
3.2. Effect of sample volume
AC
2.4.4. Determination of Co in pharmaceutical samples
Solid phase extraction with using AC-HNMABA coupled
with FAAS method of determination was applied to determine
cobalt in pharmaceutical samples. The contents of vitamin B12
as Cobalt in four ampoules for injection were decomposed in
a 50 ml round-bottom flask by heating with a 5.0 ml mixture
containing concentrated nitric and sulfuric acids (10:1) on a hot
plate until near dryness [31]. A drop wise addition of concentrated nitric acid was needed to obtain a colorless residue. The
residue was neutralized with a dilute sodium hydroxide solution, and was then diluted to an appropriate volume (50 ml). The
cobalt contents were analyzed using 2.0 ml of the solutions by
the recommended procedure. A standard method using NitrosoR salt has also been used [32] as a reference method. The results
are given in Table 5.
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2.4.5. Determination of Zn in a milk sample
A sample of powdered milk (1.0 g) was heated in a beaker
containing mixture of concentrated sulphuric acid (10 ml) and
nitric acid (4 ml) till a clear solution was obtained. It was allowed
to cool and most of the acid was neutralized with sodium hydroxide. The pH was adjusted to optimum value and the volume was
made up to 500 ml. The concentration of zinc was estimated by
passing the solution through the column packed with HNMABA
loaded AC. The metal ion was eluted from the column using 6 ml
of 1 M nitric acid in acetone and determined using FAAS. The
average (three determinations) amount of zinc was found to be
38.55 g g−1 (R.S.D. ∼4.28%). The reported value of zinc in
the milk sample is 38.0 g g−1 . The determination of zinc in a
powdered milk sample was performed in triplicate. The results
obtained (38.0 g g−1 ± 4.28%) were in good agreement with
those reported for this sample (38.0 g g−1 ), which indicates the
suitability of this method for zinc determination in this kind of
matrix.
3. Results and discussion
3.1. Effect of pH
pH is an important parameter, because its significantly affects
the metal–AC-HNMABA complex formation. The effect of pH
and complexation of metal ions with AC-HNMABA was studied
The effect of sample volume on the elution of Co, Ni, Zn and
Cd was studied by taking different volumes of various samples,
100, 200, 300, 400, 500, 600 and 700 ml. The extraction was
carried out as described in the earlier procedure. In all cases the
recovery obtained was higher than 98.5% for all these elements.
However, the efficiency of recovery slightly decreases when the
sample volume was more than 60 ml. Hence, 600 ml of water
sample was chosen for the present study.
3.3. Effect of flow rate of sample volume
The degree of metal ion sorption on AC-HNMABA was
studied by varying the flow rate of the metal ion solution
(sample solution). The optimum flow rate for loading all these
metal ions was 0.5–3.0 ml min−1 . As flow rate increases beyond
3.0 ml min−1 , there was a decrease in the percentage of sorption
of metal ions. Hence, 3.0 ml of sample solution was chosen for
further investigation. The obtained results were represented in
Fig. 2.
3.4. Total sorption capacity
A volume of 150 ml solution containing 100 g of each
metal (pH 5.0 ± 0.2) was placed in contact with 0.5 g of ACHNMABA at constant stirring (rpm) during 24 h and the sorption
capacity of the AC-HNMABA was determined by column
method. The solid matrix was filtered and washed with double distilled water. Then the sorbed metal ions were eluted with
6.0 ml of 1 M HNO3 in acetone and determined by FAAS to calculate sorption capacity of the column. The results obtained are
reported in Table 2 (discuss above results). The batch method
was also used to determine the sorption capacity and similar
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K. Kiran et al. / Journal of Hazardous Materials 147 (2007) 15–20
Table 2
Analytical parameters
Experimental parameters
Metal ions
pH range
Flow rate (ml min−1 )
Sorption capacity (mol−1 g)
Average recovery (%)
Standard deviation
Relative standard deviation (%)
Co(II)
Cu(II)
Ni(II)
Zn(II)
Cd(II)
5.0
0.5–1.5
223
99.6
0.048
4.390
5.0
1.0–3.0
465
97.8
0.036
3.780
5.0
2.0–3.0
259
98.7
0.020
2.279
5.0
0.5–2.5
195
99.0
0.029
2.750
5.0
1.5–2.5
98
97.2
0.037
4.018
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able for Co, Cd, Ni and Zn. Therefore, AC-HNMABA seems
to be a better sorbent in simultaneous sorption of the studied
elements at pH 5.0 ± 0.2.
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3.6. Preconcentration and recovery of metal ions
AC
Enrichment factor was determined by increases the dilution
of metal ion solution increasing metal dilution while keeping the
total amount of loaded metal ion fixed at 15 g for Cd and 20 g
for Co, Cu, Zn or Ni and applying the recommended column procedure. The preconcentration factors for Co(II), Cu(II), Ni(II),
Zn(II) and Cd(II) are 175, 310, 100, 299 and 246, respectively,
are shown in Table 3.
Fig. 2. Effect of flow rate on sorption capacity of metal ions.
3.7. Method evaluation
3.5. Preconcentration efficiency
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results were obtained. It was found to be nearly same (variation
<5%) by the two methods.
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The efficiency of the AC-HNMABA column for the sorption of metals was studied by using 450 mg of AC-HNMABA
in comparison with 450 mg of AC for preconcentration of metals in a model solution. Starting with 40 g of each metal in
50 ml of solution, the quantity of unretained metals in the filtrate was determined by FAAS. The percentage sorption of the
metals retained on the sorbents was calculated from the difference between the starting amount of each metal (mg) (Ns )
and the amount of metal (mg) left in the filtrate (Nf ). The ACHNMABA can retain all the metal ions while the untreated AC
cannot quantitatively retain Co, Cd, Ni and Zn. Evidently, the
preconcentration of the metals with the untreated AC is not suit-
The proposed column preconcentration solid phase extraction
method was critically evaluated with regard to reproducibility,
accuracy and detection limit.
3.7.1. Reproducibility
To test the reproducibility of proposed column solid phase
extraction method, four repetitive analysis cycles of each sample
were run. A %R.S.D. in the range 0.6–6.0 were obtained as
shown in Tables 5 and 6.
3.7.2. Accuracy
The accuracy of the proposed column preconcentration solid
phase extraction method was evaluated by comparing the results
with those obtained by the reported method [33]. The results
shown in Tables 5 and 6 reveals that the good correlation between
the two methods indicative of present method is more sensitive
than the reported method in the literature [33].
Table 3
Enrichment factor for the determination of Co, Cu, Ni, Zn and Cd with HNMABA impregnated on activated carbon using SPE in various water, pharmaceutical and
milk samples
Metal ion
Total volume (ml)
Concentration (ng ml−1 )
Final volume
Recovery
Preconcentration factora
Preconcentration factor [33]
Co(II)
Cu(II)
Ni(II)
Zn(II)
Cd(II)
2500
3000
1000
3000
2500
8.0
6.7
20.0
5.0
10.0
15
10
10
10
10
98.2
98.3
98.3
98.6
97.6
175
310
100
299
246
167
300
100
300
250
a
Present method.
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K. Kiran et al. / Journal of Hazardous Materials 147 (2007) 15–20
Table 4
Tolerance limit of electrolytes
Table 5
Determination of cobalt in B12 vitamin ampoules
Foreign species
Sample
Cobalt founda (g ml−1 );
R.S.D. (%, n = 4)
Cobalt foundb (g ml−1 );
R.S.D. (%, n = 4)
1
2
44.9 ± 1.2
46.8 ± 0.9
45.3 ± 2.4
46.7 ± 1.5
Cu(II)
Ni(II)
Zn(II)
Cd(II)
0.150
0.035
0.015
0.030
0.200
0.145
0.150
0.160
7.0
0.560
0.460
0.007
0.325
0.500
0.085
0.550
0.100
0.690
0.050
0.300
0.700
26.0
0.380
1.100
0.005
0.055
0.150
0.025
0.460
0.020
0.255
0.090
0.220
0.500
16.0
0.655
0.115
0.002
0.220
0.300
0.015
0.060
0.085
0.070
0.220
0.280
0.500
9.0
0.215
0.150
0.004
0.515
0.090
0.075
0.180
0.010
0.150
0.020
0.075
0.020
13.0
0.750
0.800
0.009
0.300
3.7.3. Detection limits
Under optimized conditions the detection limits for the determination of metal ions using column preconcentration solid
phase extraction method was presented in Table 1.
Present method.
Standard method using Nitroso-R salt [32].
(Table 4). These values indicate that sorption on AC-HNMABA
is not much sensitive to foreign species.
4. Applications
To evaluate the applicability of the preconcentration and
solid phase extraction of metal ions, it was applied to the
determination of Co(II), Cu(II), Ni(II), Zn(II) and Cd(II) in
pharmaceutical, water and milk samples. The analytical data
summarized in Tables 5 and 6 suggest that the percentage of
the recovery of metal ions ranges from 98.50 to 99.82% which
is more reliable and sensitive than the metal reported in the
literature.
It is evident from the data in Table 7 that the proposed method
is rapid, economical and more sensitive.
AC
3.8. Effect of electrolytes and cations
a
b
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NaCl
NaBr (mol l−1 )
NaNO3 (mol l−1 )
Na3 PO4 (mol l−1 )
(NH4 )2 SO4 (mol l−1 )
Na(I) (mol l−1 )
Ca(II) (mol l−1 )
Mg(II) (mol l−1 )
Humic acid (g ml−1 )
Ascorbic acid (mmol l−1 )
Citric acid (mmol l−1 )
EDTA (mmol l−1 )
Tartaric acid (mmol l−1 )
Co(II)
TE
(mol l−1 )
Metal ion
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R
The effect of electrolytes NaCl, NaF, NaNO3 , Na2 SO4 and
Na3 PO4 , NaI and other foreign species on the sorption of Co(II),
Cu(II), Ni(II), Zn(II) and Cd(II) onto AC-HNMABA matrixes
were studied. According to [33] a species is considered to interfere when it lowers the recovery of metal ions more than 2.5% in
comparison to the value observed in its absence. Each reported
tolerance/interference is in the preconcentration and not in the
determination by AAS, as checked with the help of reagent
matched standard solutions. The tolerance limits of various foreign species in the sorption of all the metal ions were studied
5. Conclusion
The sorption capacities of the present method are compared
with those of other chelating matrices. It shows in some cases
(particularly those having Amberlite XAD-2 as support) higher
capacities in comparison to others may be obtained in terms of
metals with very few exceptions. A simultaneous preconcentration method for Co(II), Cu(II), Ni(II), Zn(II) and Cd(II) from
aqueous solutions on using an activated carbon impregnated
Table 6
Determination of metal ions in water samples
Sample collected
River
watera
R
Tap waterb
Method
Metal ion (g ml−1 )
Co (R.S.D.)
Cu (R.S.D.)
Mn (R.S.D.)
Zn (R.S.D.)
Direct
S.A.
12.8 ± 1.9
13.0 ± 1.2
Direct
S.A.
14.6 ± 0.9
14.9 ± 1.2
Cd (R.S.D.)
19.7 ± 1.2
20.1 ± 0.8
6.2 ± 3.2
6.4 ± 3.0
3.4 ± 3.2
3.1 ± 5.8
4.0 ± 6.0
4.3 ± 3.5
24.6 ± 1.3
24.4 ± 0.6
12.8 ± 1.4
13.4 ± 1.2
14.6 ± 1.6
14.5 ± 0.8
7.2 ± 2.6
7.0 ± 1.6
Direct, recommended procedure is directly applied; S.A., standard addition method; R.S.D. (%), for four determinations.
a River water collected near Renigunta industrial area.
b Collected tap water from Chandragiri Gram panchayats.
Table 7
Comparison of the present method with the reported methods
Reagent
Instrumentation
Detection limits (g ml−1 )
References
Diethyldithiocarbamates
Chloromethylated polysterene-PAN
Pyrrolidine dithiocarbamate
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K. Kiran et al. / Journal of Hazardous Materials 147 (2007) 15–20
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with 2-{[1-(2-hydroxynaphthyl) methylidene] amino} benzoic
acid column and batch methods were developed. The results
obtained shows that the proposed method can be applicable for
the determination of trace metal ions in variety of environmental and pharmaceutical samples with low detection limit, high
accuracy and precision.