Selective and sensitized spectrophotometric determination of trace amounts of Ni(II) ion using α-benzyl dioxime in surfactant media

Spectrochimica Acta Part A 66 (2007) 295–301

Selective and sensitized spectrophotometric determination of trace amounts of Ni(II) ion using ␣-benzyl dioxime in surfactant media Mehrorang Ghaedi ∗ Chemistry Department, Yasouj University, Yasouj 75914-353, Iran Received 16 October 2005; accepted 24 February 2006

Abstract Highly sensitive and interference-free sensitized spectrophotometric method for the determination of Ni(II) ions is described. The method is based on the reaction between Ni(II) ion and benzyl dioxime in micellar media in the presence of sodium dodecyl sulfate (SDS). The absorbance is linear from 0.1 up to 25.0 ␮g mL−1 in aqueous solution with repeatability (RSD) of 1.0% at a concentration of 1 ␮g mL−1 and a detection limit of 0.12 ng mL−1 and molar absorption coefficient of 68,600 L mol−1 cm−1 . The influence of reaction variables including type and amount of surfactant, pH, and amount of ligand and complexation time and the effect of interfering ions are investigated. The proposed procedure was applied to the determination of trace amounts of Ni(II) ion in tap water, river water, chocolate and vegetable without separation or organic solvent extraction. © 2006 Elsevier B.V. All rights reserved. Keywords: ␣-Benzyl dioxime (BDO); Spectrophotometric method; Surfactant media; Sodium dodecyl sulfate (SDS); Nickel(II) ion

1. Introduction The determination of heavy metals in environmental samples such as water samples is a task for analytical chemists frequently asked by environmentalists, for the evaluation and phenomena interpretation of aquatic systems. There is a growing interest in nickel determination. Nickel is moderately toxic element as compared with other transition metals. However, it is known that inhalation of nickel and its compounds can lead to serious problems, including respiratory cancer [1]. Moreover, nickel can cause a skin disorder known as nickel–eczema [2]. The determination of nickel is important due to its toxic nature and its presence in industrial wastes and various other effluents. Nickel is present in low concentrations in raw meat, chocolates, hydrogenated oils, milk and milk products and canned food, etc. Cancer of nasal cavity and lungs, dermatitis, asthma, acute pneumonitis and disorders of central nervous system may be caused by nickel toxicity. The direct determination of traces of this ion from natural waters is limited and difficult when its concentration is too low to be determined directly and/or interference due to the matrix cannot be eliminated. In most cases pretreatment of samples, physical separation and non-universal instrumentation are required. ∗

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Due to low level of this element for their simple and ease spectrophotometric determination in various biological and industrial sample an aggregation and solubilization is required, that can be achieved using surfactants [3]. Micellar systems are convenient to use because they are optically transparent, readily available and stable [4]. In the field of metal ion complexation, at concentrations below or above the critical micelles concentration (CMC), micelles form a ternary complex with advantageous properties, such as hyperchromic and bathochromic displacements, that can modify sensitivity of the method by affecting the interferences and matrix effects [5]. The ability of micellar system to solubilize slightly insoluble or even very insoluble complexes and/or ligands has been used to enhance the analytical merit of given methods [6–8]. The ability of micelles to solubilize complexes in aqueous solution can eliminate the need for non-aqueous extraction step in a given analysis [6,9,10], which reduces the cost and toxicity of the method. Since, organic ions and molecule can bind the surfactant assemblies by electrostatic and hydrophobic interaction, therefore methods based on surfactants lead to modification and improving sensitivity, which emerged from the fact that non-polar part of solute molecules has a strong interaction with the exposed hydrocarbon chains of the surfactant and lead to improvement in method characteristics performance. Consequently, many analytical procedures have been proposed for nickel determination, such as voltammetry [11,12],

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on-line preconcentration [13], ion selective electrode [14,15], polarography [16]. Many of these methods are time consuming or require complicated and expensive instrument and some of them has low repeatability and need more care for sensor preparation. However, the spectrophotometric method still has the advantages simplicity and requires no expensive or complicated test equipments. For this reason, a wide variety of spectrophotometric method for the determination of nickel have been reported [17–33]. Each chromogenic reagent has its advantages and disadvantages with respect to sensitivity, selectivity and rapidity. The most widely used reagents for nickel determination have been the oxime compounds, containing the group –C( NOH)–, which reacts selectively with nickel. A large number of oxime is used for spectrophotometric determination of trace amount of nickel ion [27,31]. Due to the well known effect of surfactants in extraction system which emerged from their ability in phase separation, solvent extraction, especially in surfactant media have been successfully applied in the extraction, preconcentration and purification of many species especially in the separation of metal ions [34–36]. Thus, analytical methods based on sensitized spectrophotometric reagents are often sufficiently sensitive to permit measurements in the nano to micro molar range and can exhibit good sensitivity emit an intense absorbance peak, allowing trace ion determination by conventional spectrofotometry. In the present work a simple and highly selective and sensitive spectrophotometric method for determination of nickel(II) ions using BDO in surfactant media (SDS) was established. The effect of various parameters such as pH, type and amount of surfactant and amount of ligand were examined. Time dependency of complex and effect of interference of other metal ions were evaluated. The method has wide linear range, low detection limit, high sensitivity and selectivity and high repeatability that successfully have been used for determination of Ni(II) ion content in real samples. 2. Experimental 2.1. Instrumentation A Shimadzu UV–vis 160 spectrophotometer was used to measure the absorbance of complex in SDS media. To adjust the pH and prepare the buffer solution a 691 pH/ion meter with a combined glass and calomel electrode has been used. The Ni(II) ion determinations was carried out on a Perkin-Elmer 603 atomic absorption spectrometer with a hollow cathode lamp and a deuterium background corrector, at an air–acetylene flame under the recommended conditions. 2.2. Reagent and solution All chemicals such as nitrate of Ni(II) ion and other cation were of the analytical grade purchased from Merck Company. A 0.5% (w/v) all surfactant all from Merck company including sodium dodecyl sulfate (SDS), Triton X100, Brij 58, cetyltrimethylammonium bromide (CTAB), n-

dodecytrimethylammonium bromide (DTAB) was prepared by dissolving 0.5 g of surfactant in 100 mL volumetric flask with stirring. The ligand benzyl dioxime (BDO) was purchased from Merck company and used without further purification. 2.3. Procedure calibration curve Standard Ni(II) solutions were prepared in the range of 0.05–30.0 ␮g mL−1 . Several aliquots of Ni(II) ion were added to 10 mL volumetric flask, and 0.8 mL of 0.1 M BDO and 0.6 mL of 0.07 M SDS were added to each flask, then 2 mL 0.01 M NaOH was added and filled to the mark and calibration curve of Ni(II) was constructed using a UV–vis 160 spectrometer. 2.4. Pretreatment of water samples Analysis of water samples for determination of Ni(II) ion content was carried out as follows: 250 mL of river water or spring water was poured in a beaker and 30 mL concentrated HNO3 and 10 mL of H2 O2 of (30%) for elimination and decomposition of organic compound were added. While stirring, it heated to reach its volume to one tenth. After adjustment of samples pH to desired value the spectrophotometric experiment was performed according to general described procedure. A synthetic sample was prepared. 2.5. Chocolate pretreatment A 20 g chocolate sample was ashed in silica crucible for 4 h on a hot plate and the charred material was transferred to furnace for overnight heating at 450 ◦ C. The residue was cooled and treated with 10.0 mL concentrated nitric acid and 3 mL 30% H2 O2 again kept in furnace for 2 h at the same temperature so that no organic compound traces are left. The final residue was treated with 0.5 mL concentrated hydrochloric acid and 1–2 mL 70% perchloric acid and evaporated to fumes, so that all the nickel metal changes to nickel ions. The solid residue was dissolved in water and filtered. By keeping the pH at 12 by addition of KOH the spectrophotometric procedure has been carried out. The dissolved solution was suitably diluted and metals concentrations were determined with UV–vis spectrophotometer. 2.6. Soil sample pretreatment Homogenized soil sample 20 g was weighed accurately and in a 200 mL beaker was digested in the presence of an oxidizing agent, following the method recommended by Jacson [36] then 10 mL Concentrated HNO3 and 2 mL HClO4 70% was added and heated for 1 h. The content of beaker was filtered through a Whatman No. 40 filter paper into a 250 mL calibrated flask and its pH was adjusted to desired value and diluted to mark with de-ionized water. In all of real and synthetic sample amount of Ni(II) ion was found by standard addition method.

M. Ghaedi / Spectrochimica Acta Part A 66 (2007) 295–301

3. Results and discussion In surfactant media complexes of metal ions with complexing agent are most stable and formed aggregates that cause an improvement in sensitivity and detection limits. Recently sensitized spectrophotometric determinations of various species based on surfactant media have been reported. 3.1. Aabsorption spectra of Ni(BDO)2 in SDS media After Ni(II), BDO and SDS were added to a 10 mL volumetric flask so that their concentrations were 2.0 × 10−6 M, 8.0 × 10−3 M and 4.2 × 10−3 M, respectively, the solution was diluted to the mark at pH 12. Then, the absorption spectrum of Ni(BDO)2 in the presence and absence of SDS was obtained, which is shown in Fig. 1. Experiment in micellar media has higher sensitivity without need to extraction of complex to organic phase. The studies focused on investigation of complexation between nickel ion and BDO in micellar media and evaluating optimum conditions for its sensitized spectrophotometric determination. The stability and decomposition rate of complex seriously depend on pH and time. The low sensitivity and omitting spectra in acidic media is an indication. At optimum pH the time dependency and rate of complex formation was investigated. The effect of various parameters such as pH, type and amount of surfactant and amount of ligand were examined. Time dependency of complex and effect of interference of other metal ions were evaluated. The method has wide linear range, low detection limit, high sensitivity and selectivity and high repeatability that successfully have been used for determination of Ni(II) ion content in real samples. The color of Ni(II)–BDO complex in aqueous media in the presence of surfactant has high dependency to the reactant addition order. (Addition of surfactant before ligand lead to orange color and addition of Ni(II) ion in the end lead to a red color), which the desired complex has high time dependency. The desired complex has high solubility in alkali media with pH,

Fig. 1. Comparing spectra in the presence and absence of surfactant at optimum condition of reagents and 10 ␮g mL−1 Ni(II), according to Table 5.

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i.e. pH 12.0, although the sensitivity can be improved by addition of suitable surfactant. After Ni(II), BDO and SDS were added to a 10 mL volumetric flask so that their concentrations were 8.0 × 10−7 M, 4.2 × 10−3 M SDS and 8 × 10−3 M BDO, respectively and was diluted to the mark with 0.01 m KOH. The absorption spectrum of complex in the presence and absence of SDS was obtained, which is shown in Fig. 1. The red color complex after stirring for 8 min quantitatively formed and can be used for spectrophotometric determination of Ni(II) ion. The method has advantages including no need to extraction of complex to organic phase, rapid, need to harmful organic solvent and simple. The studies focused on investigation of complexation between Ni(II) and BDO in micellar media and evaluating optimum conditions for sensitized spectrophotometric determination of Ni(II) ion using BDO. 3.2. Effect of pH on sensitivity In order to investigate the effect of acidity on the absorbance of proposed system, the absorbance of desired complex in 4.2 × 10−3 SDS media for its quantitative determination with the BDO in micellar media was investigated over the range of 9–13. Results, which are shown in Fig. 2 indicate that the Ni(BDO)2 complex showed the maximum absorption in alkaline pH 12.0. At pH <12 the intensity of the desired complex decreases most probably due to partial hydrolysis of nickel ion. We assume that the reaction to form this complex could has competed against ligand protonation at lower pH which lead to incomplete complex formation and lower sensitivity. 3.3. Effect of surfactant on sensitivity The desired complex and BDO has good water solubility in alkaline media, but sensitivity of its complex in the absence of surfactants is low. To improve the sensitivity, the effect of type and concentration of different surfactants on the reaction were examined. To ensure the effect of types of surfactants, Triton X-100 and Brij 58 as non-ionic, sodium dodecylsul-

Fig. 2. Effect of pH on sensitivity of Ni(II) in Micellar media according to Table 5.

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Table 1 Effect of type of surfactants on method sensitivity at conditions according to Table 5 Type of surfactant

Absorbance

λ max (nm)

SDS CTMAB DTMAB Triton X-100 No

0.57 0.37 0.39 0.44 0.25

562 552 554 560 554

fate (SDS) as anionic surfactant and cetyltrimethylammonium bromide (CTMAB) and n-dodecyltrimethylammonium bromide (DTMAB) as cathionic surfactant on the absorbance of above mention complex were studied. As shown in Table 1, 4.2 × 10−3 SDS media below its CMC [37,38], the calibration curve with high sensitivity and red shift could be constructed and its slope was approximately c.a. two times more than in the absence of surfactant. In other media spectra can be obtained with lower sensitivity, so SDS was selected for further studies. This observation that in the presence of anionic surfactant, method had high sensitivity suggests that complex interacts with the SDS as anionic surfactant by hydrophobic solvation of the chelate in addition to electrostatic interaction which cause increase in solubility. It seems that BDO combines with Ni(II) ion to form a more polar complexes, and the complexes is extracted instantaneously into the local polar environment of micelle of anionic surfactant, with a SDS were somewhat less than micelle concentration. The desired complex was homogenously dissolved in micellar media with molar absorptivity of 68,600 L mol−1 cm−1 . 3.4. Effect of SDS concentration The various concentration of SDS was added to solutions at optimum and sensitivity was examined. Results are shown in Fig. 3. When the concentration of SDS surfactant less than its critical micelle concentration, the homogeneous solution is formed at a point where Ni(II)–BDO complex can be well dis-

Fig. 4. Effect of BDO concentration on sensitivity at optimum conditions according to Table 5.

solved. With the concentration of SDS varying from 8.0 × 10−6 to 8.0 × 10−3 at pH 6.0 for BDO the absorbance of desired complexes at concentration of 10 ␮g mL−1 Ni(II) ion was investigated. The absorbance increases sharply with increasing in SDS concentration and then level off, reach a maximum absorbance in the 4.2 × 10−3 M concentration of SDS. 3.5. Effect of BDO concentration on sensitivity The concentration of BDO has a deep effect on the absorbance of the nickel complex. For this evaluation at fixed value of other parameters, for a 10 ␮g mL−1 Ni(II) ion, under the established conditions various amount of ligand was added to similar solutions at optimum conditions. Results which are shown in Fig. 4 show that maximum absorbance was observed at ligand concentration higher than 8 mM (a 20-fold excess of ligand regardless of Ni(II) ion concentration within the linear range). So we added BDO more than 20 times Ni(II) concentration to reduce fluctuation in measurement. 3.6. Investigation of the composition of complex and order of reactants

Fig. 3. Effect of SDS concntration on sensitivity of Ni(II) ion according to Table 5.

The examination of the reactants order on sensitivity and the rate of complex formation was tested closely based on the fact that at temperature about 15 ◦ C has not significant effects on reaction rate. Thus at room temperature after 5 min at fix concentration of reactant and varying them alternatively, the order of reactant was calculated as 1:1:2 for SDS:Ni(II):BDO. It is mentionable that order of addition of reagents are very important. If first added ligand and nickel ion then SDS was added, a orange complex can be formed, while reverse addition lead to formation of a red complex. The choice of suitable complexation time requires a trade-off between sensitivity, speed and selectivity. The various complexation time on method sensitivity was examined, which results illustrated in Fig. 5 show that after 8 min reaction time maximum sensitivity can be obtained.

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Table 4 Investigation of accuracy and precision of proposed methods for real sample analysis Samplea

Ni(II) added

Ni(II) founded

Founded by AAS

Recovery (%)

River water

0.0 1.0

0.564 ± 0.004 1.583 ± 0.002

0.568 ± 0.004 1.61 ± 0.003

– 102

Soil sample

0.0 1.0

0.314 ± 0.005 1.304 ± 0.002

– 1.34 ± 0.002

99.0

Chocolate

0 0.8

0.726 ± 0.002 1.531 ± 0.002

– 1.537 ± 0.002

– 100.5

Spring sample

0 0.7

0.250 ± 0.003 0.963 ± 0.002

– 1.367 ± 0.002

– 102

a

Fig. 5. Effect of complexation time on sensitivity at optimum conditions. Table 2 Investigation of method repeatability at conditions according to Table 5 No

Absorbance

1 2 3 4 5 6 7 Mean RSD (%)

0.578 0.589 0.568 0.578 0.580 0.567 0.574 0.576 1.3

3.7. Calibration curve and detection limit A calibration plot for the determination Ni(II) ion was prepared according to the general procedure under the optimum conditions developed above from the sensitized spectrophotometric method with various concentration of this ion. The dynamic range of Ni(II) was 0.1–25.0 ␮g mL−1 with correlation coefficient (R2 ) of 0.9989 for which show the good linearity of calibration curve. Based on the signals of ten blank solutions Table 3 Investigation of tolerance limit of interfering ions on the recovery of 2 ␮g mL−1 Ni(II) ion Interfering ion

[Ion]/[Ni(II)]

Co2+ Cu2+ Pb2+ Ag+ Hg2+ Zn2+ Cd2+ Mg2+ K+ Ba2+ Fe2+ Cr3+ Al3+

30 50 300 300 300 500 500 600 1000 600 200 300 400

All value are ␮g mL−1 .

and the slope of calibration curve, it was found that the detection limit was 0.12 ng mL−1 . 3.8. Examination of reproducibility In order to investigate reproducibility of method at optimum condition six experiments at optimum conditions has been performed and results are brought in Table 2. The results show that repeatable results can be obtained that indicate repeatable results. The result of repeatability as RDS for 10 ␮g mL−1 Ni(II) ion is 1.3%. 3.9. Interference effect The effect of potential interfering ions on the determination of Ni(II) ion at optimum condition were investigated by addition known concentrations of each ion to a fix Ni(II) ion concentration and measurement of the absorbance in the presence and absence of various amount of common interfering ion that concomitant with nickel in real samples. If the sensitivity and extraction efficiency in the presence and absence of interfering ion does not differ more that 5% analyte signal in the absence of the interfering ion, does not interfere. Therefore various amount of interfering ion was added to 1 ␮g mL−1 of Ni(II) Table 5 Figures of merit of proposed method Parameter

Value

Ligand concentration (mM) pH Linear range (␮g mL−1 ) Regression equation Surfactant and its concentration (M) Equilibration time (min) Solvent Selectivity Detection limit (ng mL−1 ) Accuracy and precision Advantages

8 12 0.1 − 25.0 A = 0.0934CNi 2+ − 0.0046 4.2 mM SDS 8 Water High 0.12 High High repeatability, sensitivity, selectivity, wide linear range and no need to organic solvent Do not preconcentrate

Disadvantages

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Table 6 Comparison of charastristic performance of developed method with some similar reported method Reagent

Medium/solvent

Interfering ion

λ max (nm)

ε

L.R.a

Reference

Azocalix[4]arene PANS QADP 5-Me-BtAMB 6-Me-BTAESB QADEAA APDC BPGO SAOBH CBDAB DBMCA p-Acetyl arsenazo PAN

Aqeous pH 11.7, pH 5–10, chloroform pH 9.0, chloroform Aqeous pH 6.5, SDS Aqeous pH 5.6, SDS Aqeous pH 6.0, SDS Aqeous pH 2–10, Tween 80 Carbontetrachloride pH 6–9 Aqueous, pH 6 Aqueous, pH 10 Aqueous Aqueous Gasoline, pH 3–10

Co(II) Cu(II), Co(II), Zn(II), Fe(III), Pd(II), Mn(II) Cu(II), Co(II), Zn(II), Fe(III), V(V) Cu(II), Co(II), Pd(II), Ag(I), Fe(II) Cu(II), Co(II), Ag(I), Ti(IV), Fe(II) Co(II), Ag(I) Cu(II), Co(II), Cd(II), Pb(II), Bi(II) Cu(II), Cr(III), Al(III), Zn(II), Fe(III), Bi(II)

580 570 574 640 620 590 340 267 405 540 625 640 568

128000 56000 124000 132000 82200 138000 – 22500 302500 330000 10380 60300 –

0.01–0.3 0.1–1.0 0.04–0.72 0–0.4 0–0.6 0.01–0.4 Low linear 0.1–5.0 11.7–117.4 Up to 0.24 0.01–0.79 0–0.8 Up to 0.8

[20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [32] [33]

Zn(II) Ca(II), Ba(II) – Cu(II), Fe(III), Mn(II), Pb(II), Zn(II)

Abbreviation: 5-Me-BTAMB, 2-[2-(5-methylbenzothiazolyl)azo]-5-dimethylaminobenzoic aci; DPKBH, di-2-pyridylketonebenzoylhydrazone; ATT, 2acetylthiophene thiocyanate; 6-Me-BTAMSB, 2-[2-(6-methylbenzothiazolyl)azo]-5-(N-ethyl-N-sulfomethyl)aminobenzoic acid; QADEAP, 2-(2-quinolylazo)-5diethylaminophenol; QADP, 2-[2-(4-methylquinolyl)azo]-5-diethylaminophenol; PANS, 1-(2-pyridylazo)-2-naphtol-6-sulfonic acid; QADEAA, 2-(2-quinolylazo)5-diethylaminoaniline; APDC, ammonium pyrolydinedithiocarbamate; BPGO, 4-Benzyl-1-piperazineglyoxime; SAOBH, salicylaldehyde 3-oxobutanoylhydrazone; CBDAB, o-carboxylbenzenediazo-aminoazobenzene; DBMCA, dibromo-p-methyl-carboxyazo. a All value are ␮g mL−1 .

ion and results are shown in Table 3. Results display that among the ions studied, some ion could be tolerated up to the mg level. The method has good selectivity even in the presence of cobalt and copper ion. This unique selectivity is due to high pH. 3.10. Analytical application in real samples In order to test the performance of the proposed method, the aforementioned method was applied to predict the concentration of this ion in soil sample, vegetable, chocolate, spring and river water. Reliabilities were checked by spiking experiments and independent analysis. To ensure that the method is valid and has reasonable accuracy and precision, recovery of the Ni(II) ions in the river water and the tab water were determined by the proposed technique and the results are shown in Table 4 has not significant difference with reference AAS method based on t-test. The low relative standard deviations represent the high reproducibility in these measurements. Therefore, this proposed technique could be applied to the determination of ng mL−1 level of Ni(II) ion in real samples (Tables 5 and 6). 4. Conclusion The optimum value of parameters are presented in Table 5. The proposed method offers the advantages of simplicity, selectivity and high sensitivity for the determination of Ni(II) ion without the need for organic solvent extraction, preconcentration or pre-separation. An efficient analytical method for determining the determination Ni(II) was successfully developed by using a sensitized spectrophotometric using BDO. The method due advantages such as high selectivity and sensitivity, low detection limit, simplicity, low cost and no need to extraction and using organic harmful solvent with respect to previously reported methods (Table 6) is an alternative method for nickel determination.

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