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Journal of Analytical Methods in Chemistry
Volume 2012, Article ID 713862, 8pages
doi:10.1155/2012/713862
Research Article
A Green Preconcentration Method for Determination of
Cobalt and Lead in Fresh Surface and Waste Water Samples Prior
to Flame Atomic Absorption Spectrometry
Naeemullah, Tasneem Gul Kazi, Faheem Shah, Hassan Imran Afridi, Sumaira Khan,
Sadaf Sadia Arian, and Kapil Dev Brahman
National Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro 76080, Pakistan
Correspondence should be addressed to Naeemullah, naeemullah433@yahoo.com
Received 4 July 2012; Accepted 5 October 2012
Academic Editor: Jolanta Kumirska
Copyright © 2012 Naeemullah et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Cloud point extraction (CPE) has been used for the preconcentration and simultaneous determination of cobalt (Co) and lead
(Pb) in fresh and wastewater samples. The extraction of analytes from aqueous samples was performed in the presence of 8-
hydroxyquinoline (oxine) as a chelating agent and Triton X-114 as a nonionic surfactant. Experiments were conducted to assess
the effect of different chemical variables such as pH, amounts of reagents (oxine and Triton X-114), temperature, incubation time,
and sample volume. After phase separation, based on the cloud point, the surfactant-rich phase was diluted with acidic ethanol
prior to its analysis by the flame atomic absorption spectrometry (FAAS). The enhancement factors 70 and 50 with detection
limits of 0.26 µgL
−1and 0.44 µgL
−1were obtained for Co and Pb, respectively. In order to validate the developed method, a
certified reference material (SRM 1643e) was analyzed and the determined values obtained were in a good agreement with the
certified values. The proposed method was applied successfully to the determination of Co and Pb in a fresh surface and waste
water sample.
1. Introduction
Release of large quantities of metals into the environment
(especially in natural water) is responsible for a number of
environmental problems [1]. Metals are major pollutants in
marine, ground, industrial, and even treated waste waters
[2]. Industrial wastes are the major source of various kinds of
toxic metals which have nonbiodegradability and persistence
properties resulted in a number of public health problems
[3]. Metals of interest, cobalt (Co) and lead (Pb), were chosen
based on their industrial applications and potential pollution
impact on the environment [4].
Pb is a toxic metal and widely distributed in the
environment. It is an accumulative toxic metal, which is
responsible for a number of health problems [5].
Pb reaches humans from natural as well as anthropogenic
sources, for example, drinking water, soils, industrial emis-
sions, car exhaust, and contaminated food and beverages.
Therefore, highly sensitive and selective methods have
needed to be developed to determine the trace level of Pb
in water samples. The maximum contaminant levels of Pb in
drinking water allowed by environmental protection agency
(EPA) is 15.0 µgL
−1, while the world health organization
(WHO) for drinking water quality containing the guideline
value of 10 µgL
−1[6,7].
Co is known to be an essential micronutrient for
metabolic processes in both plants and animals [8]. It is
mainly found in rocks, soil, water, plants, and animals. The
determination of trace level of Co in natural waters is very
important because Co is important for living species and it
is part of vitamin B12 [9]. Exposures to a high level of Co
lead to serious public health problems and are responsible
for several diseases in human such as in lung, heart, and skin
[10].
Flame atomic absorption spectrometry (FAAS) is a
widely used technique for quantification of metal species.
The determination of metals in water samples is usually
associated with a step of preconcentration of the analyte
2Journal of Analytical Methods in Chemistry
before detection [11]. The determination of trace levels of
Pb and Co in water samples is particularly difficult because
of the usually low concentration; on the bases of these facts a
great effort is needed to develop highly sensitive and selective
methods to simultaneously determine trace level of these
metals in water samples [12,13].
A variety of procedures for preconcentration of metals,
such as solid phase extraction (SPE) [14], liquid-liquid
extraction (LLE) [15], and coprecipitation and cloud point
extraction (CPE) [16] have been developed. Among them,
CPE is one of the most reliable and sophisticated separation
methods for the enrichment of trace metals from different
types of samples. While other methods such as LLE are
usually time consuming and labor intensive and require
relatively large volumes of solvents, which are not only
responsible for public health problems but also a major
cause of environmental pollution [17–22]. It was reported
in literature that Pb and Co had been preconcentrated
by CPE method after the formation of sparingly water-
soluble complexes with different chelating agents such as
ammonium pyrrolidine dithiocarbamate (APDC) [23,24]1-
(2-thiazolylazo)-2-naphthol (TAN) [25], 1-(2-pyridylazo)-
2-naphthol (PAN) [26,27], and diethyldithiocarbamate
(DDTC) [28–30].
In the present work, we introduce a simple, sensitive,
selective, and low-cost procedure for simultaneous precon-
centration of Co and Pb after the formation of complex with
oxine, using Triton X-114 as surfactant and later analysis by
flame atomic absorption spectrometry. Several experimental
variables affecting the sensitivity and stability of separa-
tion/preconcentration method were investigated in detail.
The proposed method was applied for the determination of
traceamountofbothmetalsinfreshsurfaceandwastewater
samples.
2. Experimental
2.1. Chemical Reagents and Glassware. Ultrapure water,
obtained from ELGA lab water system (Bucks, UK), was used
throughout the work. The nonionic surfactant Triton X-114
was obtained from Sigma (St. Louis, MO, USA) and was used
without further purification. Stock standard solution of Pb
and Co at a concentration of 1000 µgL
−1was obtained from
the Fluka Kamica (Bush, Switzerland). Working standard
solutions were obtained by appropriate dilution of the stock
standard solutions before analysis. Concentrated nitric acid
andhydrochloricacidwereanalyticalreagentgradefrom
Merck (Darmstadt, Germany) and were checked for possible
trace Pb and Co contamination by preparing blanks for each
procedure. The 8-hydroxyquinoline (oxine) was obtained
from Merck, prepared by dissolving appropriate amount of
reagent in 10 mL ethanol and diluting to 100 mL with 0.01 M
acetic acid, and were kept in a refrigerator 4◦C for one week.
The 0.1 M acetate and phosphate buffer were used to control
the pH of the solutions. The pH of the samples was adjusted
to the desired pH by the addition of 0.1 mol L−1HCl/NaOH
solution in the buffers. For the accuracy of methodology, a
certified reference material of water SRM-1643e, National
Institute of Standards and Technology (NIST, Gaithersburg,
MD, USA) was used. The glass and plastic wares were soaked
in 10% nitric acid overnight and rinsed many times with
deionized water prior to use to avoid contamination.
2.2. Instrumentation. A centrifuge of WIROWKA Laborato-
ryjna type WE-1, nr-6933 (speed range 0–6000 rpm, timer 0–
60 min, 220/50 Hz, Mechanika Phecyzyjna, Poland) was used
for centrifugation. The pH was measured by pH meter (720-
pH meter, Metrohm). Global positioning system (iFinder
GPS, Lowrance, Mexico) was used for sampling locations.
A Perkin Elmer Model 700 (Norwalk, CT, USA) atomic
absorption spectrometer, equipped with hollow cathode
lamps and an air-acetylene burner. The instrumental param-
eters were as follows: wavelength 240.7 and 283.3nm and
slit widths: 0.2 and 0.7 nm for Co and Pb. Deuterium lamp
background correction was also used.
2.3. Sample Collection and Preparation Procedure. The fresh
surface water samples (canals) and waste water were collected
on alternate month in 2011 from twenty (20) different sam-
pling sites of Jamshoro, Sindh (southern part of Pakistan)
with the help of the global positioning system (GPS). The
understudy district positioned between 25◦19–26◦42 N and
67◦12–68◦02 E. The sampling network was designed to
cover a wide range of the whole district. The industrial waste
water samples of understudy areas were also collected. All
water samples were filtered through a 0.45 micropore size
membrane filter to remove suspended particulate matter and
were stored at 4◦C.
2.4. General Procedure for CPE. For Co and Pb deter-
mination, aliquot of 25 mL of the standard or sample
solution containing both analytes (20–100 µg/L), oxine 5 ×
10−3mol L−1and Triton X-114 0.5% (v/v), were added. To
reach the cloud point temperature, the system was allowed
to stand for about 30 min into an ultrasonic bath at 50◦C
for 10 min. Separation of the two phases was achieved by
centrifuging for 10 min at 3500 rpm. The contents of tubes
were cooled down in an ice bath for 10 min. The supernatant
was then decanted by inverting the tube. The surfactant-
rich phase was treated with 200 µLof0.1molL
−1HNO3
in ethanol (1 : 1, v/v) in order to reduce its viscosity and
facilitate sample handling. The final solution was introduced
into the flame by conventional aspiration. Blank solution was
submitted to the same procedure and measured in parallel to
the standards and real samples.
3. Result and Discussion
3.1. Optimization of CPE. The preconcentration of Pb and
Co was based on the formation of a neutral, hydrophobic
complex with oxine, which is subsequently trapped in the
micellar phase of a nonionic surfactant (Triton X-114).
Utilizing the thermally induced phase extraction separation
process known as CPE, the analyte is highly preconcentrated
and free of interferences in a very small micellar phase. Sev-
eral parameters play a significant role in the performance of
Journal of Analytical Methods in Chemistry 3
the surfactant system that is used and its ability to aggregate,
thus entrapping the analyte species. The pH, complexing
reagent and surfactant concentration, temperature, and time
were studied for optimum analytical signals.
3.2. Effect of pH. The effect of pH on the CPE of Co and Pb
was investigated because this parameter plays an important
role in metal-chelate formation. The effect of pH upon the
extraction of Co and Pb ions from the six replicate standard
solutions 20.0 µgL
−1was studied within the pH range of 3–
10, while each operational desired pH value was obtained by
the addition of 0.1 mol L−1of HNO3/NaOH in the presence
of acetate/borate buffer. The maximum extraction efficiency
of understudy metals was obtained at pH range of 6.5–7.5 as
shown in Figure 1, for subsequent work pH 7.0 was chosen
as the optimum for subsequent work.
3.3. Effect of Triton X-114 Concentration. Separation of metal
ions by a cloud point method involves the prior formation
of a complex with sufficient hydrophobicity to be extracted
in a small volume of surfactant-rich phase. The temper-
ature corresponding to cloud point is correlated with the
hydrophilic property of surfactants. The nonionic surfactant
Triton X-114 was chosen as surfactant due to its low cloud
point temperature and high density of the surfactant-rich
phase, which facilitates phase separation by centrifugation.
The effect of Triton X-114 concentrations on the extraction
efficiencies of Co and Pb were examined at the range of 0.1
to 1.0% (v/v). Figure 2 shows that quantitative extraction
was observed when surfactant concentration was >0.5%
(v/v). At lower concentrations, the extraction efficiency of
complexes was low probably because of the inadequacy of the
assemblies to entrap the hydrophobic complex quantitatively.
A Triton X-114 concentration of 0.5% (v/v) was selected for
subsequent studies.
3.4. Effect of Oxine Concentration. The oxine is a relatively
very stable and selective hydrophobic complexing reagent
which reacts with both selected cations. Replicate 10 mL
of standard, SRM, and real sample solution in 0.5% (w/v)
Triton X-114 at a buffer of pH 7.0 and complexed with oxine
solutions in the range of 1.0–10.0 ×10−3mol L−1. The results
revealed in Figure 3 that extraction efficiency of both metals
increases up to 5 ×10−3mol L−1. This value was, therefore,
selected as the optimal chelating agent concentration. The
concentrations above this value have no significant effect on
the efficiency of CPE.
3.5. Effects of Sample Volume on Preconcentration Factor. The
preconcentration factor (PCF) is defined as the concentra-
tion ratio of the analyte in the final diluted surfactant-rich
extract ready for its determination and in the initial solution.
Among the other factors, this depends on the phase rela-
tionship, on the distribution constant of the analyte between
the phases, and on sample volume. The sample volume is
one of the most important parameters in the development
of the preconcentration method, since it determines the
sensitivity and enhancement of the technique. The phase
0
20
40
60
80
100
2345678910
pH
Pb
Co
Recovery (%)
Figure 1: Effect of pH on the percentage of recover y: 20 µgL
−1
of Pb and Co, 5.0×10−3mol L−1oxine, 0.5% (v/v) Triton X-114,
temperature 50◦C, and centrifugation time 10 min (3500 rpm).
0
20
40
60
80
100
0 0.2 0.4 0.6 0.8 1
Triton X-114 (%v/v)
Recovery (%)
Pb
Co
Figure 2: EffectofTritonX-114onthepercentageofrecovery:
20 µgL
−1of Pb and Co, 5.0×10−3mol L−1oxine, pH 7.0,
temperature 50◦C, and centrifugation time 10 min (3500 rpm).
0246810
20
40
60
80
100
Recovery (%)
Coxine (1 ×10−3mol L−1)
Pb
Co
Figure 3: Effect of oxine concentration on the percentage of
recovery : 20 µgL
−1of Pb and Co, 0.5% (v/v) Triton X-114, pH 7.0,
temperature 50◦C, and centrifugation time 10 min (3500 rpm).
4Journal of Analytical Methods in Chemistry
Tab le 1: Influences of some foreign ions on the recoveries of cobalt and lead (20 µgL
−1) determination by applied CPE method.
Ion Concentration (µgL
−1)Pbrecovery(%)Corecovery(%)
Na+20000 97 ±2.14 98 ±2.22
K+5000 98 ±2.21 99 ±3.02
Ca2+ 5000 98 ±2.12 97 ±1.12
Mg2+ 5000 97 ±1.04 98 ±3.08
Cl−30000 99 ±2.05 98 ±3.04
F−1000 96 ±3.01 97 ±1.12
NO3−3000 97 ±1.04 98 ±3.06
HCO3
−1000 98 ±3.12 97 ±2.04
Al3+ 500 97 ±2.21 99 ±3.05
Fe3+ 50 96 ±2.23 97 ±3.02
Zn2+ 100 97 ±3.05 96 ±2.32
Cr3+ 100 96 ±2.08 98 ±2.25
Cd2+ 100 97 ±3.12 98 ±3.22
Ni2+ 100 96 ±2.23 97 ±3.01
Tab le 2: Analytical characteristics of the proposed method.
Element condition Concentration range (µgL
−1)SlopeInterceptR2R.S.D. (n=5)aLODb(µgL
−1)
Co without preconcentration 250–5000 3.97 ×10−3−0.013 0.9871 1.45 (500) 32.0
Co with preconcentration 20.0–100 0.279 +0.008 0.9997 2.22 (20) 0.26
Pb without preconcentration 250–5000 5.03 ×10−3−0.034 0.9972 0.88 (600) 46.0
Pb with preconcentration 20.0–100 0.256 −0.012 0.9989 1.88 (30) 0.44
aValues in parentheses are the Co and Pb concentrations (µgL
−1) for which the RSD was obtained.
bLimit of detection, calculated as three times the standard deviation of the blank signal.
Tab le 3: Determination of cobalt and lead in certified reference material and water samples.
(a)
Certified reference material Certified values (µgL
−1) Measured values (µgL
−1) Percentage of recovery (RSD %)
Co Pb Co Pb Co Pb
SRM 1643e 27.06 ±0.319.63 ±0.226.8±0.82 19.24 ±0.5 99.0% (3.06%) 98.0% (2.60%)
(b)
Samples Added (µgL
−1) Measured (µgL
−1)Recovery(%)
Co Pb Co Pb Co Pb
Canal water
003.34 ±0.962 6.08 ±0.781 — —
225.32 ±0.384 8.06 ±0.822 99.8 99
558.33 ±0.432 11.0±0.784 100 98.4
10 10 13.3±0.642 15.9±0.828 99.6 98.2
Mean ±SD (n=3).
Tab le 4: Determination of lead and cobalt in water samples.
Sample Co (µgL
−1)Pb(µgL
−1)
Canal water 3.34 ±0.962 6.08 ±0.781
Waste w a t e r 14.6±1.20 17.3±1.52
Mean ±SD (n=3).
ratio is an important factor, which has an effect on the
extraction recovery of cations. A low phases ratio improves
the recovery of analytes, but decreases the preconcentration
factor. However, to determine the optimum amount of the
phase ratio, different volumes of a water sample 10–1000 mL
and a constant volume of surfactant solution 0.5% were
chosen. The obtained results show that with increasing the
sample volume >100 mL, the extracted understudy analytes
were decreased as compared to those obtained with 25–
50 mL. A successful cloud point extraction should maximize
the extraction efficiency by minimizing the phase volume
ratio, thus improving its concentration factor. In the present
work, the initial sample volume was 25 mL and the final
volume of surfactant rich phase after diluted with acidic
ethanol was 0.5 mL, hence the PCF achieved in this work was
50 for both understudy analytes.
Journal of Analytical Methods in Chemistry 5
Tab le 5: Comparative table for determination of cobalt and lead in different types of samples applying CPE before analysis by atomic
spectrometric technique.
Reagent and surfactant Matrix and technique PFaand EFbLODc(µgL
−1) Reference
Cobalt
TAN/Triton X-114 Water/(FAAS) —/57b0.24 [25]
PAN/TX-100 Water samples/(GFAAS) —/100b0.003 [31]
PAN/TX-114 Urine/(FAAS) —/115b0.38 [32]
5-Br-PADAP/TX-100-SDS Pharmaceutical samples/(FAAS) —/29b1.1 [14]
TAN/Triton X-100 Water/(GFAAS) —/100b0.003 [33]
APDC/Triton X-114 Biological tissues/(TS-FF-FAAS) —/130b2.1 [34]
APDC/Triton X-114 Water/(FAAS) —/20b5.0 [23]
1,2-N,N /PONPE 7.5 Water sample/(FAAS) —/27b1.22 [35]
Me-BTABr/Triton X-114 Water sample/(FAAS) —/28b0.9 [36]
Oxine/Triton X-114 Water sample/(FAAS) 50/50 0.44 Present work
Lead
DDTP/Triton X-114 Human hair/(FAAS) —/43b2.86 [28]
PONPE 7.5/— Human saliva/(FAAS) —/10b—[37]
APDC/Triton X-114 Certified biological reference materials/(ETAAS) —/22.5b0.04c/— [24]
DDTP/Triton X-114 Certified blood reference samples/(ETAAS) —/34b0.08 [38]
PONPE 7.5/— Tap water certified reference material/(ICP-OES) —/>300b0.07 [39]
DDTP/Triton X-114 Riverine and sea water enriched water reference materials/(ICP-MS) —/— 40.0 [40]
5-Br-PADAP/Triton X-114 Water/(GFAAS) 50a/—0.08c/— [41]
PAN/Triton X-114 Water/(FAAS) —/55.6b1.1 [27]
—/Tween 80 Environmental sample/FAAS 10a/—7.2 [42]
TAN/Triton X-114 Water sample/(FAAS) 15.1a/—4.5 [43]
Pyrogallol/Triton X-114 Water sample/(FAAS) 72a/—0.4 [44]
Oxine/Triton X-114 Water sample/(FAAS) 50/70 0.26 Present work
apreconcentration factor, benhancement factor, and climit of detection.
3.6. Interferences. The interference is those relating to the
preconcentration step, which may react with oxine and
decrease the extraction. To perform this study, 25 mL
solution containing 20 µg/L−1of both metals at different
interference to analyte ratio were subjected to the developed
procedure. Tab le 1 shows the tolerance limits of the interfer-
ing ions error <5%. The tolerance limit of coexisting ions
is defined as the largest amount making variation of less
than 5% in the recovery of analytes. The effects of represen-
tative potential interfering species were tested. Commonly
encountered matrix components such as alkali and alkaline
earth elements generally do not form stable complexes under
the experimental conditions. A high concentration of oxine
reagent was used, for the complete chelation of the selected
ions even in the presence of interferent ions.
3.7. Analytical Figures of Merit. The calibration graph
using the preconcentration step for Co and Pb were
linear with a concentration range of 5.0–20 ug L−1of
standards and subjecting to CPE methods at optimum
levels of all understudy variables. The extracted analytes
in diluted micellar media were introduced into the flame
by conventional aspiration. Tab l e 2 gives the calibration
parameters for the proposed CPE method including the
linear ranges, relative standard deviation RSD, and limit
of detection LOD. The experimental enhancement factors
calculated as the ratio of the slopes of calibration graphs with
and without preconcentration. The enhancement factors of
Co and Pb subjected to CPE method were found to be 70 and
50, respectively. The limits of detection LOD were calculated
as the ratio between three times the standard deviation
of ten blank readings and the slope of the calibration
curve after preconcentration were calculated as 0.26 and
0.44 µgL
−1, respectively, for Co and Pb. The obtained LOD
was sufficiently low for detecting trace levels of Co and Pb in
different types of fresh and waste water samples.
The accuracy of the proposed method was evaluated by
analyzing a standard reference material of water SRM-1643e
with certified values of Co and Pb content. It was found that
there is no significant difference between results obtained
by the proposed method and the certified results of both
metals. Reliability of the proposed method was also checked
by spiking both metals at to three concentration levels (2.0–
10.0 µgL
−1) in a real water sample. The results are presented
in Tables 3(a) and 3(b). The perecentage of recoveries (R)of
spike standards were calculated as follows:
R(%)=(Cm−Co)
m×100, (1)
where Cmis a value of metal in a spiked sample, Cothe value
of metal in a sample, and mis the amount of metal spiked.
6Journal of Analytical Methods in Chemistry
These results demonstrate the applicability of developed
procedure for Co and Pb determination in different water
samples.
3.8. Application to Real Samples. The CPE procedure was
applied to determine Co and Pb in fresh surface and waste
water samples. The results are shown in Tab le 4. The Co and
Pb concentrations in fresh surface water were found in the
range of 2.12–5.12 µgL
−1and 1.49–8.56 µgL
−1,respectively.
In waste water, the levels of both analyte were high, found in
the range of 13.6–16.8 and 15.1–19.4 µgL
−1for Co and Pb,
respectively.
4. Conclusion
In this study, Triton X-114 was chosen for the formation of
the surfactant-rich phase due to its excellent physicochemical
characteristics, low cloud point temperature, high density of
the surfactant-rich phase, which facilitates phase separation
easily by centrifugation, and commercial availability and
relatively low price and low toxicity. This method is a
promising alternative for the determination of Co and
Pb linked with FAAS. From the results obtained, it can
be considered that oxine is an efficient ligand for cloud
point extraction of Co and Pb. The simple accessibility, the
formation of stable complexes, and consistency with the
cloud point extraction method are the major advantages
of the use of oxine in cloud point extraction of Co and
Pb. CPE has been shown to be a practicable and versatile
method, being adequate for environmental studies. Cloud
point extraction is an easy, safe, rapid, inexpensive, and
environmentally friendly methodology for preconcentration
and separation of trace metals in aqueous solutions. The
surfactant-rich phase can be directly introduced into flame
atomic absorption spectrometer FAAS after dilution with
acidic ethanol. The proposed CPE method incorporating
oxine as chelating agent permits effective separation and
preconcentration of Co and Pb and final determination
by FAAS provides a novel route for trace determination
of these metals in water samples of different ecosystem.
A low-cost surfactant was used, thus toxic organic solvent
extraction generating waste disposal problems was avoided.
The comparison of the results found in the presented study
and some works in the literature was given in [31–44].
The proposed cloud point extraction method is superior
for having lower detection limits when compared to other
methods as shown in Tabl e 5 .
Acknowledgment
The authors would like to thank the National center of
Excellence in Analytical Chemistry (NCEAC), University
of Sindh, Jamshoro, for providing financial support and
excellent research lab facilities for scholars to carry out the
research work.
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