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Journal of Saudi Chemical Society (2012) 16, 451–459
King Saud University
Journal of Saudi Chemical Society
www.ksu.edu.sawww.sciencedirect.com
ORIGINAL ARTICLE
Study of the solid phase extraction and spectrophotometric
determination of nickel using 5-(40-chlorophenylazo)-6-
hydroxypyrimidine-2,4-dione in environmental samples
Alaa S. Amina,*, Amirah S. AL-Attas
b
a Chemistry Department, Faculty of Science, Benha University, Benha, Egyptb Chemistry Department, King Abdul Aziz University, Girls College of Education, Saudi Arabia
Received 7 December 2010; accepted 21 February 2011
Available online 5 March 2011
*
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A
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KEYWORDS
Pyrimidine azo dyes;
Nickel determination;
Spectrophotometry;
Solid phase extraction;
Environmental analysis
Corresponding author. Ad
ent of Medical Science, Umm
rabia. Tel.: +966 596269644
-mail address: asamin2005@
19-6103 ª 2011 King Saud
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osting by E
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Abstract A rapid, sensitive and selective method for the determination of nickel based on the rapid
reaction of nickel(II) with 5-(40-chlorophenylazo)-6-hydroxypyrimidine-2,4-dione (CPAHPD) and
the solid phase extraction of the Ni(II)–CPAHPD complex with C18 membrane disks has been
developed. In the presence of pH 6.8 buffer solution and cetylpyridinium bromide (CPB) medium,
CPAHPD reacts with nickel to form a red complex of a molar ratio of 1:1 (nickel to CPAHPD).
This complex was enriched by solid phase extraction (SPE) with C18 membrane disks. An enrich-
ment factor of 100 was obtained by elution of the complex from the disks with the minimal amount
of isopentyl alcohol. The molar absorptivity and Sandell sensitivity of the complex was
3.11 · 105 L mol�1 cm�1 and 0.0189 ng cm�2, respectively at 549 nm in the measured solution.
Beer’s law was obeyed in the range of 0.01–0.37 lg mL�1, while that obtained by Ringbom plot
was in the range of 0.025–0.35 lg mL�1. The detection and quantification limits were calculated
culty of Community, Depart-
a University, Makkah, Saudi
0 133222568.
com (A.S. Amin).
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452 A.S. Amin, A.S. AL-Attas
and found to be 0.003 and 0.01 lg mL�1. The proposed method was applied to the determination of
nickel in water, food, biological and soil samples with good results.
ª 2011 King Saud University. Production and hosting by Elsevier B.V.
Open access under CC BY-NC-ND license.1. Introduction
The determination of heavy metals in environmental samplessuch as water and biological samples is a task for analyticalchemists frequently asked by environmentalists, for the evalu-
ation and phenomena interpretation of aquatic systems. In re-cent years, the toxicity and the effect of trace elements onhuman health and the environment are receiving increasing
attention in pollution and nutritional studies. Nickel was longthought to be essential to plants and some domestic animals(Wang, 1991), but not considered to be a metal of biological
importance until 1975, when Zerner discovered that ureasewas a nickel enzyme (Zerner, 1991; Thauer, 2001). It is knownthat inhalation of nickel and its compounds can lead to seriousproblems, including nasopharynx, lung and dermatological
diseases and malignant tumors (Kalyakina et al., 2003;Kristiansen et al., 2000). So, separation of toxic Ni(II) is of in-tense current interest in research and environmental cleanup.
The traditional preconcentration and separation methods formetal ions are liquid–liquid extraction, coprecipitation, andion-exchange, etc. These methods often require large amounts
of high purity organic solvents, some of which are harmful tohealth and cause environmental problems (Liu et al., 2004).Nowadays, the SPE is being widely utilized for preconcentra-tion or separation of metals due to the following advantages.
These include (Liu et al., 2005): (1) higher enrichment factors;(2) absence of emulsion; (3) safety with respect to hazardoussamples; (4) minimal costs due to low consumption of re-
agents; (5) flexibility; (6) ease of automation.Nickel is one of the essential micronutrients for plants, ani-
mals, and humans, but is toxic at elevated concentrations
(Krstic et al., 2007; Soylak, 2002). Compared with other tran-sition metals, nickel is a moderately toxic element (Soylak andDogan, 1996; Amini et al., 2009). For example, nickel can
cause a skin disorder known as nickel-eczema (Soylak andDogan, 1996; Amini et al., 2009; Saraji and Yousefi, 2009).Therefore, the accurate and sensitive determination of nickelin environmental samples is very important.
The biological monitoring of trace amounts of nickel hasreceived considerable attention (Akesson and Skervfing,1985; Easton et al., 1994), because excessive exposure to cer-
tain nickel compounds in biological tissues and fluids may re-sult in genotoxicity or carcinogenesis. Many analyticalmethods such as neutron activation analysis (Byrne and
Krasovec, 1988), inductively coupled plasma mass spectrome-try (Ponce de Leon et al., 2002), atomic absorption spectrom-etry (Wang and Hansen, 2001; Narin et al., 2000), atomic
emission spectrometry (Barnett, 1987), flame atomic absorp-tion spectrometry (Ghaedi et al., 2005, 2008a,b; Soylaket al., 1999, 2007, 2010; Soylak and Elci, 2000; Yebra et al.,2008; Mohammadi et al., 2010; Dadfarnia et al., 2010), modi-
fied activated carbons (Ghaedi et al., 2008a,b) and spectropho-tometry (Vicente et al., 2002) have been developed for thedetermination of nickel. The first two methods have disadvan-
tages in terms of cost and instruments in routine analysis.These methods generally require sample pretreatment and
infrastructure backup and are therefore, not very convenientfor routine analysis of large number of environmental samples.
However, the spectrophotometric method still has theadvantages of simplicity and of not requiring expensive orcomplicated test equipment. This has led to the development
of a wide variety of spectrophotometric methods for the deter-mination of nickel (Fan et al., 1998; Ma et al., 2001; Luciaet al., 1999; Fan and Zhu, 1998; Zhao et al., 1994; Ishizukiet al., 1993; Barreto et al., 2010; Sarma et al., 2008; Antunes
et al., 2009). Routine spectrophotometric methods are oftennot sensitive enough to determine low concentrations of nickelion in environmental samples, i.e. nickel concentrations less
than the lg L�1 level. Consequently, a preconcentration stepis usually required. SPE is an attractive technique because ofits notable advantages (Garg et al., 1999; Hu et al., 2002;
Haddad et al., 1999). The presented paper, based on the colorreaction of CPAHPD with nickel and the SPE of the coloredcomplex with C18 disks, describes the development of a highly
rapid, sensitive and selective method for the determination ofnickel in water, food, biological and soil samples.
2. Experimental
2.1. Apparatus
A Perkin–Elmer Lambda 12 UV–visible spectrophotometerwith a 10 mm quartz cell was used for all spectral measure-
ments. The extraction was performed on Waters SPE Device(that can prepare 20 samples simultaneously), and ZorbaxC18 membrane disks [47 mm (diameter), 0.5 mm (thickness),
8.0 lm, 50 mg] (Agilent Technologies, USA) were used. A Per-kin–Elmer atomic absorption spectrometry model A Analyst300 was used for all AAS measurements. An Orion research
model 601 A/digital ionalyzer pH meter was used for checkingthe pH of solutions.
2.2. Reagent
All chemicals used were of analytical grade unless otherwisestated. All the solutions were prepared with ultra-pure water
obtained from a Milli-Q50 SP Reagent Water System(Millipore Corporation, USA). High purity isopentyl alcohol(Fisher Corporation, USA) was used. 5-(40-Chloropheny-
lazo)-6-hydroxypyrimidine-2,4-dione used in the present inves-tigation was prepared according to the procedure describedpreviously (Amin and Mohammed, 2001). An accurate weightof CPAHPD was dissolved in 100 mL of absolute ethanol to
prepare 1 · 10�3 M solution.A stock standard solution of nickel 1 · 10�3 M, was pre-
pared from nickel sulphate hexahydrate (Aldrich product)
and standardized gravimetrically with dimethylglyoxime(Vogel, 1964). Working solutions were prepared by appropri-ate dilution with de-ionized distilled water. A hexamine–
hydrochloric acid buffer solution, 0.5 M with a pH 6.8 con-taining 0.1 M sodium thiosulfate and 0.2 M sodium fluoride,
Study of the solid phase extraction and spectrophotometric determination of nickel 453
was used. CPB (Fluka product) solution (2.0% (m/v)) was pre-
pared by dissolving CPB with water.
2.3. General procedure
To a standard or sample solution containing no more than1.85 lg of Ni(II) in a 250 mL measuring flask, 15 mL of0.5 M hexamine–hydrochloric acid buffer solution with pH
6.8, 5.0 mL of 1 · 10�3 M CPAHPD solution and 4.0 mL of2.0% CPB (m/v) solution were added. The mixture was dilutedto 250 mL with water and mixed well. After 5.0 min, the
solution was passed through the C18 disks at a flow rate of50 mL min�1. After the enrichment, the retained complexwas eluted from the disks with 5.0 mL of isopentyl alcohol
at a flow rate of 5.0 mL min�1. The absorbance of the eluentwas measured in a 10 mm cell at 549 nm against a reagentblank prepared in a similar way without nickel.
0
0.2
0.4
0.6
0.8
1
1.2
Abs
orba
nce
2.4. Procedure for food samples
The analytical procedure was used for nickel determination in
several natural samples such as starch, sugar, black tea leaves,tobacco and rice flour. These samples were homogenized anddried overnight at 70 �C, and were kept in dry ambient. A
dry-ashing sample preparation was carried out for a samplemass of 1.0 g, which was decomposed at 500 �C for 60 min, fol-lowed by a treatment with 20 mL concentrated nitric acid anda second step of heating for 45 min. The solution was boiled
almost to dryness. This was cooled and then 10 mL of waterwas added to dissolve the salts. The solution was transferredto a 25 mL standard flask, 1.0 mL of 9.0% (w/v) thiourea solu-
tion and 2.0 mL of 2.0% (w/v) sodium fluoride solution wereadded to prevent the interference of Al3+, Fe3+ Co2+,Pd2+, Cu2+, and Zn2+. Then the experimental general proce-
dure was followed to complete the determination.
340 380 420 460 500 540 580 620 660 700Wavelength (nm)
Figure 1 Absorption spectra for (A) 10�3 M CPAHPD (. . ...)
and (B) its complex with 0.2 lg mL�1 Ni(II) (___) at the optimum
reaction conditions.
0.8
1
1.2
e
2.5. Procedure for human hair sample
An accurately weighed 0.20 g of Human hair sample wasplaced in the Teflon high-pressure microwave acid digestionbomb (Fei Yue Analytical Instrument Factory, Shanghai,
China). 2.5 mL of concentrated nitric acid and 2.5 mL of30% (v/v) hydrogen peroxide were added. The bombs weresealed tightly and then positioned in the carousel of the micro-
wave oven. The system was operated at full power for 6.0 min.The digest was evaporated to near dryness. The residue wasdissolved with 1.0% of HCl (v/v), and the nickel contents were
analyzed according to general procedure described above.
0
0.2
0.4
0.6
2 3 4 5 6 7 8 9 10pH
Abs
orba
nc
Figure 2 Effect of pH on the absorbance of 0.2 lg mL�1 Ni(II)
complexed with 10�3 M CAPHPD under the optimum reaction
conditions.
2.6. Soil sample pretreatment
Homogenized soil sample 2.0 g was weighed accurately and ina 200 mL beaker was digested in the presence of an oxidizingagent, following the Jacson method (Jacson, 1965) then
10 mL concentrated HNO3 and 2.0 mL of 70% HClO4 (v/v)was added and heated for 1 h. The content of beaker wasfiltered through a Whatman No. 40 filter paper into a
250 mL calibrated flask and its pH was adjusted to desiredvalue and diluted to mark with de-ionized water. In all of realand synthetic sample amount of Ni(II) ion was found by stan-
dard addition method.
2.7. Procedure for water samples
The samples (5.0 L) were acidified with hydrochloric acid,filtered with a 0.45 lm filter, heated and evaporated to
250 mL. The nickel contents were analyzed according togeneral procedure described above. A standard method usingthe above general procedure and AAS has been used as a
reference method.
3. Results and discussion
3.1. Absorption spectra
The absorption spectra of CPAHPD and its Ni(II) complex inisopentyl alcohol medium are represented in Fig. 1. Theabsorption peaks of CPAHPD and its complex are located
at 423 nm and 549 nm, respectively.
454 A.S. Amin, A.S. AL-Attas
3.2. Effect of buffer
Different types of buffers were examined (borate, acetate, hex-amine, phosphate, thiel and universal buffers). Results show
that the optimal pH for the reaction of Ni(II) with CPAHPDwas slightly acidic medium. A hexamine–hydrochloric acidbuffer solution was found to be the optimal one. Moreover,
the optimum pH value for complexation was pH from 5.8 to7.8 (Fig. 2). The pH 6.8 is recommended to control pH, asthe use of 12–18 mL buffer solution per 250 mL of final solu-tion was found to give a maximum and constant absorbance.
The use of 15 mL of buffer solution is recommended. Theuse of basic medium, cause decomposition of the complexand formation of nickel hydroxide which has a high solubility
product prevent the complexation and preconcentration pro-cess. The buffer solution containing a 0.08–0.15 M of sodiumthiosulfate and 0.15–0.25 M of sodium fluoride can increase
the selectivity of this system [without sodium thiosulfate andsodium fluoride in the buffer solution, the tolerance limits offoreign ions were 0.7 mg for Cu(II), Zn(II); 0.85 mg for
Fe(III), Pd(II). However, the tolerance limits of foreign ionsreached 0.22 mg for Fe(III); 0.03 mg for Cu(II), Zn(II);0.035 mg for Pd(II), when sodium thiosulfate and sodium fluo-ride existed in the buffer solution]. So 0.1 mol L�1 of sodium
thiosulfate and 0.2 M of sodium fluoride in buffer are recom-mended. The influence of sodium thiosulfate and sodium fluo-ride on absorbance of nickel solution and its extracted complex
increase the stability constant of the complex with respect toligand.
3.3. Effect of surfactants
The Ni(II)–CPAHPD complex has a poor solubility in watersolution. It needs to add a suitable amount of surfactants to
enhance the solubility of the complex. Experiments showedthat all the non-ionic and anionic surfactants have no effectto enhance the solubility, whereas the cationic surfactants have
a good effect on the solubility of the complex formed, indicat-ing that the nickel complex has an ionic nature. In addition to
0
0.2
0.4
0.6
0.8
1
1.2
0 1 2 3 4 5 6 7CPB volume (mL)
Abs
orba
nce
Figure 3 Effect of 2.0% CPB on the complexation of
0.2 lg mL�1 Ni(II) using 10�3 M CPAHDP.
enhancing the solubility, in the cationic surfactants medium,
the sensitivity of the Ni(II)–CPAHPD complex has increasedmarkedly too. The effect of four nonionic {Triton X-100,Tween-80, Tween-20 and Emulsified–OP}, three anionic {so-dium lauryl sulphate (SLS), sodium dodecyl sulfonate (SDS)
and sodium dodecyl benzenesulfonate} and five cationic{tetradecyltrimethyl ammonium bromide (TDTAB), tricetylm-ethyllammonium bromide (CTAB), cetylpyridinium bromide
(CPB), benzyldimethyl tetradecylammonium chloride (zephir-amine), and cetylpyridinium chloride (CPC)} were studied tochoose the most favorable one which gave higher solubility
and sensitivity. CPB and CTAB surfactants improve the solu-bility and sensitivity. The results showed that CPB was the bestand a most probable additive and the use of 3.0–5.0 mL of
2.0% CPB gives a constant and maximum absorbance valuefor the studied complex (Fig. 3). Accordingly, 4.0 mL CPBsolution was recommended.
3.4. Effect of CPAHPD concentration
For up to 1.85 lg of Ni(II), different volumes of 1 · 10�3 M
CPAHPD were used to choose the optimum reagent concen-tration for complexation process. The use of about 4.0–6.0 mL of 1 · 10�3 M CPAHPD solution has been found to
be sufficient for a complete reaction. Accordingly, 5.0 mL of1 · 10�3 M CPAHPD solution was added in all further mea-surements (Fig. 4), for complete complex formation. Higherconcentrations of CPAHPD decrease the complexation due
to dissociation of the formed complex.
3.5. Stability of the chromogenic system
After mixing the components, the absorbance reached its max-imum within 5.0 min at room temperature and remained stable
for 9.0 h in aqueous solution. The complex was stable at least24 h, after it was extracted into the isopentyl alcohol medium.
3.6. Solid phase extraction
Both the enrichment and the elution were carried out on aWaters SPE device (Amin, 2009; Liu et al., 2005). The flow rate
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10 12CPAHPD volume (mL)
Abs
orba
nce
Figure 4 Effect of 10�3 M CPAHPD concentration on the
absorbance of 0.2 lg mL�1 Ni(II) at the optimum conditions.
Table 1 Analytical characteristics of the proposed methods.
Parameter Before
preconcentration
After
preconcentration
pH 6.8 6.8
kmax (nm) 543 549
Study of the solid phase extraction and spectrophotometric determination of nickel 455
was set to 50 mL min�1 for enrichment and 5.0 mL min�1 for
elution. Some experiments were carried out to investigate theretention of CPAHPD and its Ni(II) complex on the disks.The CPAHPD and its Ni(II) complex can be retained on thedisks quantitatively when they pass the disks as aqueous solu-
tion. The capacity of the disks for CPAHPD was 32 mg andfor its Ni(II)-complex 19 mg in a 250 mL of solution usingboth of the batch and column methods. The disks have ade-
quate capacity to enrich the Ni(II)–CPAHPD complex andthe excessive CPAHPD.
In choosing the proper eluent to retained CPAHPD and
its Ni(II) complex, various organic solvents were studied.The effect of various organic solvents was in the followingsequence: isopentyl alcohol > acetonitrile > dioxane > ace-
tone > ethanol > methanol. So isopentyl alcohol was selectedas the eluent. The experiment shows that it is easier to elute theretained CPAHPD and its Ni(II) complex in reverse directionthan in forward direction, so it is necessary to upturn the disks
for the elution. 5.0 mL of isopentyl alcohol was a sufficientamount to elute the CPAHPD and its Ni(II) complex fromdisks at a flow rate of 5 mL min�1. The volume of 5.0 mL elu-
ent was selected.
3.7. Nature of the complex
The stoichiometry of the complex was established at the opti-mum conditions described above using the molar ratio andcontinuous variation methods. The plot of absorbance versus
the molar ratio of CPAHPD to Ni(II), obtained by varyingthe CPAHPD concentration, showed inflection at molar ratio1.0, indicating the presence of one CPAHPD molecule in the
complex formed (Fig. 5). Moreover, Jobs method (Job, 1936)showed a ratio of CPAHPD to Ni(II) = 1.0. Consequently,the results indicated that the stoichiometric ratio was (1:1)
[Ni(II):CPAHPD]. The shape of the resulting curves indicatesthat the complex is labile. Consequently, a large excess ofreagent must be always used (upto the optimum concentration
estimated above under Section 3.4) to enhance the formationof the complex. The conditional formation constant (log K),calculated using Harvey and Manning equation (Harvey andManning, 1950):
0
0.4
0.8
1.2
1.6
2
2.4
0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4Molar ratio
Abs
orba
nce
Figure 5 Molar ratio for Ni(II) complexed with CPAHPD.
Kn ¼ ðA=AmÞ=ð1� A=AmÞnþ1CRn2
where Kn is the formation constat, CR is the reagent concentra-tion, A is the absorbance of CR, Am is the maximum absor-bance, and n is the stoichiometric ratio applying the data
obtained from the above two methods, was found to be 7.14,whereas the true constant (Amin et al., 1997) was 7.20. Theformation constant for CPAHPD was found to be 4.37 at
the same experimental conditions indicating that the highcomplexing ability to nickel.
3.8. Calibration curve and sensitivity
The calibration curve shows that Beer’s law is obeyed in theconcentration range of 0.01–0.37 lg mL�1. For more accurate
analysis, Ringbom optimum concentration ranges (Ringbom,1938) were calculated and found to be 0.025–0.35 lg mL�1.The linear regression equation obtained was:
A ¼ 5:28Cðlg mL�1Þ � 0:022; ðr ¼ 0:9995Þ:
Characteristics performance of method is presented inTable 1, The molar absorptivity was calculated to be3.11 · 105 L mol�1 cm�1 at 549 nm. The detection and quanti-
fication limits were also calculated as the standard deviationsof the absorbance measurements of 13 blank solution. The lim-its of detection (K= 3) and of quantification (K = 10) of the
method (IUPAC, 1978) were found to be 0.003 and0.01 lg mL�1, according to the IUPAC definitions (C1 =KSo/s), where C1 is the limit of detection, So is the standard er-
ror of blank, s is the slope of the standard curve and K is theconstant related to the confidence interval. The relative stan-dard deviation at a concentration level of 0.2 lg Ni(II) per mil-liliter (11 repeat determination) was 1.32%.
Stability (h) 9.0 24
Beer’s conc. range (lg mL�1) 0.1–36.8 0.01–0.37
Ringbom optimum
range (lg mL�1)
0.3–33.4 0.025–0.035
Detection limits (lg mL�1) 0.029 0.003
Quantification limits (lg mL�1) 0.1 0.01
Molar absorptivity
(L mol�1 cm�1)
3.06 · 104 3.11 · 105
Sandell sensitivity (ng cm�2) 1.85 0.0189
Regression equationa
Slope 0.259 5.28
RSD % of slope 0.0075 0.0067
Intercept +0.07 �0.022Correlation coefficient 0.9985 0.9995
RSD (%) 1.95 1. 23
Range of error (%) ±1.35 ±0.78
Calculated t-values (2.57)b 1.28 0.78
Calculated F-test (5.05)b 2.74 2.05
a A= a+ bC, where C is the concentration in lg mL�1.b Values in parentheses are the theoretical values for t- and
F-values at 95% confidence limits and five degrees of freedom.
Table 2 Comparison of the sensitivity for spectrophotometric determination of Ni(II).
Reagent kmax
(nm)
e · 10�4 L
(mol�1 cm�1)
Medium References
5-(6-Methoxy-2-benzothiazoleazo)-8-aminoquinoline 623 12.80 0.5% CTAB Zhao et al. (1999)
2-[2-(5-Methylbenzothiazolyl)azo]-5-dimethyl aminobenzoic acid 640 13.20 0.48% SDS Fan et al. (1998)
1-(2-Pyridylazo)-2-naphthol-6-sulfonic acid 570 5.60 Extr. CHCl3 Ohshita et al. (1982)
Dimethyl glyoxime 445 1.50 Bromine water Marczenko (1976)
3-(4-Methoxyphenyl)-2-mercaptopropenoic acid 415 1.95 Isoamyl alcohol Izquierdo and Carrasco (1984)
2-(2-Benzothiazolylazo)-5-dimethyl aminobenzoic acid 640 12.00 28% Methanol Furukawa (1982)
N,N-Bis(3-methylsalicylidene)-o-phenylenediamine 430 9.50 2.0% Methanol Fakharia et al. (2005)
p-Acetylarsenazo 630 6.50 Aqueous Zhao et al. (1994)
Benzothiaxolyldiazaoaminoazobenzene 550 19.60 0.8% OP Zhao et al. (1997)
5,17-Bis(quinolyl-8-azo)-25,26,27,28-tetrahydroxy 580 12.80 2.0% DMF Hu et al. (2004)
2-[2-(5-Methylbenzothiazolyl)azo]-5-dimethylaminobenzoic acid 640 13.20 Aqueous pH 6.5, SDS Ma et al. (2001)
2-[2-(6-Methylbenzothiazolyl)azo]-5-
(N-ethyl-N-sulfomethyl)aminobenzoic acid;
620 8.22 Aqueous pH 5.6, SDS Hu et al., (2003)
2-(2-Quinolylazo)-5-diethylaminoaniline 590 13.80 pH 6.0, SDS Lee and Choi (2000)
2-[2-(4-Methylquinolyl)azo]-5-diethylaminophenol 574 12.40 pH 9.0, CHCl3 Fan et al., (1998)
1-(2-Pyridylazo)-2-naphtol-6-sulfonic acid 570 5.60 pH 5–10, CHCl3 Zhao et al. (1994)
Ammonium pyrolydinedithiocarbamate 340 – Tween 80 Macit et al. (2000)
4-Benzyl-1-piperazineglyoxime 267 2.25 CCl4, pH 6–9 Kumar et al. (2004a,b)
Salicylaldehyde 3-oxobutanoylhydrazone 405 30.25 Aqueous, pH 6 Li et al. (2002)
o-Carboxylbenzenediazo-aminoazobenzene 540 33.00 Aqueous, pH 10 Kumar et al. (2004a,b)
Dibromo-p-methyl-carboxyazo 625 1.04 Aqueous Singh et al. (1979)
Benzyl dioxime 562 6.86 SDS Ghaedi (2007)
4-Methyl-8-quinolinol 450 8.09 Chloroform Suresh et al. (2008)
2-(2-Quinolinylazo)-5-dimethylaminoaniline 590 13.20 Isopentyl alcohol Hu et al. (2004)
5-(40-Chlorophenylazo)-6-hydroxypyrimidine-2,4-dione 549 31.10 pH 6.8, CPC This work
Table 3 Tolerance limits in the determination of 0.2 lg of
Ni(II) with CPAHPD (relative error ± 5.0%).
Foreign ions Tolerance limit
(lg mL�1)
Na+, K+, Li+, Cl�, ClO�4 , CH3COO� 21,000
Cetrate, thiourea, PO3�4 ;SO2�
4 ; SiO2�3 17,500
Ca2+, Mg2+, Sr2+, Ba2+, NO�3 , tartrate 14,000
Mn2+, Ce4+, SnO2�3 , Ti4+, Bi3+, F� 11,500
WO2�4 ;MoO2�
4 ;CrO24 9000
Cr3+, Ru3+, Br� 7500
Ir4+, Rh3+, I� 6000
OsO2�5 ; SeO2�
3 ;TeO2�3 4500
Hg2+, Sb3+,CN�, SCN� 3500
Be2+, Fe2+, Cd2+ 2250
Pb2+, , Ru3+, Bi3+ 1500
Gd3+, Sc3+ 1000
Al3+, La3+, Sm3+ 750
Th4+, UO42� 500
Fe3+ 220
Co2+, Pd2+ 35
Cu2+, Zn2+ 30
456 A.S. Amin, A.S. AL-Attas
The sensitivity expressed as molar absorptivity of theproposed method is compared with those of publishedspectrophotometric methods (Table 2). Although the spectro-
photometric method depending on the complexation with achromogenic reagent o-carboxylbenzenediazoaminoazoben-zene gave a higher sensitivity (3.3 · 105 L mol�1 cm�1) (Kumaret al., 2004a,b) compared with the proposed method, it suf-
fered from positive interferences of Cu(II), Fe(II), Co(II) and
Zn(II) at all concentration levels. The higher sensitivity ofthe proposed method is notable, greater even than that ofthe SPE (Hu et al., 2004) that used 2-(2-quinolinylazo)-5-dim-
ethylaminoaniline. Also, the proposed method is more sensi-tive than other methods that based on spectrophotometry(Table 2).
3.9. Interferences
A systematic study of the effect of potentially interfering spe-
cies on the nickel determination was undertaken. This studywas carried out by adding a known amount of foreign speciesto nickel solution of 0.2 lg mL�1. The tolerance limit was ta-
ken as ±5.0% change in absorbance. The results are listedin Table 3, showing that most common ions do not interferewith the determination suggesting the highly selectivity of theproposed method. Only some elements, Al3+, Fe3+ Co2+,
Pd2+, Cu2+, and Zn2+ interfered, which can be eliminatedby masking with sodium thiosulfate and sodium fluoridesolution.
3.10. Analytical applications
The proposed method has been successfully applied to thedetermination of nickel in food, plants, soil, biological andwater samples. The analytical results for the examined food,
plant and biological samples were compared with those foundby the atomic absorption spectrometry (AAS) method (Wangand Hansen, 2001), and the results shown in Table 4 were inagreement with AAS results. For the analysis of natural water
Table 5 Analytical results for the determination of trace nickel in natural water samples (5.0 L) with the proposed and AAS methods.
Samples Added (lg L�1) Founda (lg L�1)
Proposed ± SD t-Testb F-Valueb AAS ± SD
Benha lake water 0.00 1.750 ± 0.03 1.31 2.68 1.74 ± 0.05
0.50 2.242 ± 0.06 1.65 3.29 2.23 ± 0.07
1.00 2.760 ± 0.04 1.08 2.46 2.74 ± 0.06
5.00 6.745 ± 0.05 1.22 2.53 6.75 ± 0.07
River Nile water 0.00 1.335 ± 0.05 1.34 2.74 1.34 ± 0.08
0.50 1.840 ± 0.04 1.87 3.47 1.84 ± 0.06
1.00 2.345 ± 0.06 1.44 2.79 2.35 ± 0.08
5.00 6.320 ± 0.05 1.11 2.51 6.34 ± 0.06
Tap water 0.00 0.47 ± 0.03 0.98 2.31 0.46 ± 0.05
0.50 0.96 ± 0.05 1.32 2.71 0.97 ± 0.07
1.00 1.48 ± 0.02 1.15 2.59 1.47 ± 0.03
5.00 5.46 ± 0.04 1.45 2.83 5.47 ± 0.07
Makkah well water 0.00 1.82 ± 0.05 1.47 2.85 1.83 ± 0.07
0.5 2.33 ± 0.05 1.32 2.70 2.34 ±0.08
1.0 2.82 ± 0.03 1.56 3.08 2.83 ±0.05
5.0 6.52 ± 0.04 1.20 2.66 6.84 ± 0.06
Soil sample (lg g�1) Added (lg g�1)0.0 0.41 ± 0.04 0.95 2.05 0.41 ± 0.05
0.5 0.91 ± 0.06 1.14 2.37 0.92 ± 0.08
1.0 1.41 ± 0.03 1.22 2.49 1.41 ± 0.04
5.0 5.41 ± 0.02 1.48 2.89 5.41 ± 0.04
a Average of six determinations.b Theoretical values for t- and F-values at 95% confidence level for five degrees of freedom are 2.57 and 5.05, respectively.
Table 4 Analytical results of Ni(II) in plant, food and biological samples (lg g�1).
Samples Founda (lg g�1)
Proposed method t-Testb F-Valueb AAS method
Balsam pear leaves 0.51 ± 0.02 1.41 2.77 0.52 ± 0.03
Celery leaves 0.47 ± 0.03 1.25 2.49 0.48 ± 0.04
Spinach leaves 0.62 ± 0.03 1.08 2.14 0.63 ± 0.05
Black tea leaves 0.34 ± 0.02 1.22 2.38 0.34 ± 0.04
Rice flour 0.65 ± 0.02 1.11 2.15 0.64 ± 0.05
Tobacco 0.40 ± 0.04 1.38 2.61 0.39 ± 0.06
Sugar 0.61 ± 0.03 1.57 2.96 0.61 ± 0.05
Starch 0.43 ± 0.01 1.34 2.49 0.43 ± 0.03
Human hair 0.82 ± 0.04 1.61 3.13 0.81 ± 0.06
The value following ‘‘±’’ is the standard deviation.a The value following ‘‘±’’ is the standard deviation.b Theoretical values for t- and F- values at 95% confidence level for five degrees of freedom are 2.57 and 5.05, respectively.
Study of the solid phase extraction and spectrophotometric determination of nickel 457
(5.0 L) and soil samples, the standard addition method wasused, as recorded in Table 5.
In all cases, the results were compared with the AAS meth-od (Wang and Hansen, 2001). The performance of the pro-
posed method was assessed by calculation of the t-value (foraccuracy) and F-test (for precision) compared with AAS meth-od. The mean values were obtained in a Student’s t- and F-tests
at 95% confidence limits for five degrees of freedom (Millerand Miller, 2005). The results showed that the calculated val-ues (Tables 4 and 5) did not exceed the theoretical values.
Therefore, there is no significant difference between the pro-posed and the reference method, indicating that the developedmethod is as accurate and precise as the reference method(Wang and Hansen, 2001).
4. Conclusion
In this study, a highly sensitive reagent CPAHPD for nickel
determination was used. By SPE with C18 disks, an enrich-ment factor of 100 was achieved (Amin, 2009). The experi-ments showed that the molar absorptivity after SPE of
the Ni(II)–CPAHPD–CPB complex reaches 3.11 · 105 Lmol�1 cm�1 in the measured solution. The detection and quan-tification limits reached 0.003 and 0.01 lg mL�1 in the original
samples, and low concentrations of nickel in samples can bedetermined with good results. The consumption of organicsolvents in this method is much lower than that in the
liquid–liquid extraction method. By using a Waters SPEdevice, 20 samples can be prepared simultaneously. This
458 A.S. Amin, A.S. AL-Attas
method is a rapid means of simultaneously preparing large
amounts of sample.
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