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Application of mixed micelle-mediated extraction for selective separation and determination of Ti(IV) in geological and water samples
Application of mixed micelle-mediated extraction for selective separation and determination of Ti(IV) in geological and water samples Ibrahim M.M. Kenawy, Magdi E. Khalifa, Mohamed M. Hassanien, Mohamed M. Elnagar PII: DOI: Reference:
S0026-265X(15)00175-7 doi: 10.1016/j.microc.2015.08.003 MICROC 2204
To appear in:
Microchemical Journal
Received date: Revised date: Accepted date:
23 June 2015 2 August 2015 10 August 2015
Please cite this article as: Ibrahim M.M. Kenawy, Magdi E. Khalifa, Mohamed M. Hassanien, Mohamed M. Elnagar, Application of mixed micelle-mediated extraction for selective separation and determination of Ti(IV) in geological and water samples, Microchemical Journal (2015), doi: 10.1016/j.microc.2015.08.003
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ACCEPTED MANUSCRIPT Application of mixed micelle-mediated extraction for selective
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separation and determination of Ti(IV) in geological and water
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samples
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Ibrahim M.M.Kenawya, Magdi E. Khalifaa, Mohamed M. Hassanienb,
Chemistry Department, Faculty of Science, Mansoura University,
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a
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Mohamed M. Elnagara*
Mansoura, Egypt Chemistry Department, Industrial Education College, Beni-Suef
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b
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University, Beni-Suef, Egypt
ABSTRACT
A simple cloud point extraction (CPE) methodology based on the complexation
of
Ti(IV)
with
Alizarin
Red
S
(ARS)
and
cetyltrimethylammonium bromide (CTAB) at pH 3 followed by extraction with Triton X-114 in presence of Na2SO4 at room temperature (25 ºC) has been developed. The enriched analyte in the surfactant rich phase was determined by visible spectrophotometry or inductively coupled plasma optical emission spectrometry (ICP-OES). The main factors affecting mixed micelle-mediated extraction efficiency were studied. At optimum conditions, 1
ACCEPTED MANUSCRIPT the linear range of 0.3-80 and 7-200 μg L-1 with a detection limit of 0.1 and 2.3 μg L-1 were obtained for separation and determination of Ti(IV) with 50
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mL solution using ICP-OES and visible spectrophotometry, respectively. A
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pre-concentration factor of 100 was achieved for both techniques. The effect
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of diverse cations and anions on the extraction efficiency was tested. At
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optimum pH, the separation is proved to be highly selective for Ti(IV), since the extraction of many lanthanide and transition metal alizarinate complexes
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using Triton X-114 occurs at different pH ranges. The interference of 2000
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fold excess of Fe3+ is tolerated using ascorbic acid as a masking agent. Also,
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NaH2PO4 is used to eliminate the interference caused by UO22+, Zr4+, Hf4+
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and Al3+. The accuracy of the procedure was evaluated through recovery experiments on synthetic mixtures. The proposed procedure has been successfully applied for separation and determination of Ti(IV) in geological samples, simulated reference materials and water samples with satisfactory results.
Key words: Titanium; Mixed micelle-mediated extraction; Alizarin red S; Geological samples; Water samples *
To whom all correspondence should be addressed
E-mail: [email protected] 2
ACCEPTED MANUSCRIPT 1. Introduction Titanium (Ti) and its alloys have extensively numerous high-
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technological industrial applications due to their excellent characteristics
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such as high specific strength-to-weight ratio, high specific modulus, good
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oxidation and superior corrosion resistance [1]. In particular, Ti has been
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widely used in catalysis, paint pigments, rubber, textiles, and plastics [2]. The excellent corrosion resistance of Ti allows this material to be used in
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solar energy cells and as a tube material for heat exchangers or condensers in
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nuclear power plants [3, 4]. It is a valuable alloying agent and coexists in a
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number of industrially important alloys which are used principally in guided
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missiles, high-speed aircrafts, rockets, marine components and filament material in electrical applications [2]. Also, the medical application of TiO2 nanoparticles shows great promising data for potential uses as disinfectants [5], diagnostic assays [6], and tumor cell killing agents [7]. The determination of Ti(IV) in different samples has attracted considerable interest. However, direct determination of trace level of Ti in real samples by instrumental techniques is still notably difficult. The low concentration of Ti(IV) and the high complexity of the sample matrices are the main problems. Consequently, the application of separation and preconcentration techniques is of special interest in such cases. Among these, 3
ACCEPTED MANUSCRIPT solid phase extraction [8-11], ion-exchanger [12] liquid-liquid extraction [13-15] and cloud point extraction [16] were reported.
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The application of cloud point extraction (CPE) for the separation and
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pre-concentration of different metal ions [17-19], biomaterials [20] and
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organic compounds [21, 22] is of special interest. CPE technique is based on
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the property of most non-ionic surfactants to form micelles and become turbid in aqueous solution. On heating above critical temperature called
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cloud-point temperature (CPT) or by the adding of salting-out electrolytes,
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the micellar solution separates into two phases: (i) a surfactant-rich phase, in
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which the analyte ions could be pre-concentrated, and (ii) an aqueous phase
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containing surfactant at a concentration near to a critical micelle concentration (CMC). CPE has several advantages such as the separation using mild conditions, the ability to concentrate a variety of analytes with near complete recovery, speed, sensitivity, low cost and high preconcentration factors [23]. Moreover, it complies with the principles of green chemistry because of its lower toxicity to the environment than extractions that use organic solvents [24]. In this manner mixed micellemediated extraction (mixed-MME) system is becoming an important for separation and pre-concentration of many metal ions [25-27]. The use of cationic surfactants in combination with a non-ionic surfactant exhibits 4
ACCEPTED MANUSCRIPT synergism compared to a single surfactant due to higher surface activity. Moreover, the interaction of ionic surfactant with a charged complex leads
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to formation of neutral molecules which could be extracted by non-ionic
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surfactant [26, 28].
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The aim of the work was to develop a new CPE procedure for
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selective separation and pre-concentration of Ti(IV) from the commonly encountered matrix components prior to its determination using ICP-OES or
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visible spectrophotometry. The procedure is based on the complexation of
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Ti(IV) with Alizarin Red S (ARS) (Scheme 1) and the ionic surfactant
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cetyltrimethylammonium bromide (CTAB) at pH 3 followed by extraction
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with Triton X-114 (non ionic surfactant) in presence of Na2SO4. The factors affecting the efficiency of the procedure were systematically studied and optimized. At optimum conditions, the proposed procedure was applied for separation, pre-concentration and determination of Ti(IV) in water samples, simulated reference materials, synthetic mixtures and real geological samples.
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ACCEPTED MANUSCRIPT 2. Experimental 2.1. Instrumentation
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A Perkin Elmer Inductively Coupled Plasma-Optical Emission
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Spectrometry (ICP- OES, Optima 8300, USA) was used for the
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determination of Ti(IV). The optimum operation conditions for the ICP-OES
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instrument were summarized in Table 1. XRF analysis of real geological samples (wadi deposits, clay 1, clay 2 and black sand) (Table 2.) was
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performed with a PANalytical Axios Advanced XRF. A Unicam UV/Vis
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spectrometer UV2 with 1-cm quartz cell (1 mL) was used for recording
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absorption spectra in the range 400-700 nm. The pH values were adjusted
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using a Hanna instrument model 8519 pH meter (Hanna instruments, Germany) furnished with a combined glass-saturated calomel electrode. A thermostatic water bath maintained at desired temperature was used for cloud point experiments. A CH90-2 centrifuge (Hinotek Technology Co. Ltd., China) was used to speed up the phase separation.
2.2. Reagents, solutions Otherwise specified, all reagents used were of analytical reagent grade. Aqueous solutions were prepared with double distilled water. All glassware used for trace analysis were kept in 10 % (w/v) nitric acid at least 6
ACCEPTED MANUSCRIPT for 24 h and subsequently washed four times with double distilled water before use. Stock standard solution of titanium at a concentration of 1000 μg
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mL-1 was obtained from Spectrosol (BDH, England). The working standard
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solutions were freshly prepared by appropriate dilution of the stock standard
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solutions. A 5×10−3 mol L−1 solution of ARS was prepared by dissolving 1.8
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g of sodium alizarin sulphonate (Merck, Germany) in double distilled water and diluting to 1000 mL. The surfactants, Triton X-114 (obtained from
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Sigma-Aldrich, USA) and CTAB (Acros Chemicals, Ottawa, ON, Canada)
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were used without further purification. Appropriate concentrations of
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interfering ions were prepared by dissolving their nitrate salts in double
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distilled water. The pH of solutions were adjusted using hydrochloric acid– sodium acetate 1 mol L−1 (pH 1.0 - 2.5) and acetic acid–sodium acetate 0.2 mol L−1 (pH 3.0 –7.0) buffer solutions. A masking mixture was prepared by mixing equal volumes of (0.05 mol L−1 ascorbic acid, 5×10−3 NaH2PO4 and 0.05 mol L−1 thiourea) to be used for analysis of real samples, simulated reference material and synthetic mixtures.
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ACCEPTED MANUSCRIPT 2.3 Recommended procedure of mixed-MME
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In a 50 mL centrifuge tube, an aliquot of Ti(IV) standard solution was mixed with 1 mL of 5×10−3 mol L−1 ARS, 1 mL of 5×10−3 mol L−1 CTAB, 5
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ml of 1 mol L−1 Na2SO4 and 5 ml the of acetate buffer (pH 3). Then, 2.5 mL of (2 % w/v) Triton X-114 were added and final volume of micellar solution
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is brought up to 50 mL using double distilled water. The solution is then
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stirred at room temperature (25ºC) until it began to be turbid. Finally, this solution was centrifuged at 3500 rpm for 10 min in order to facilitate the
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separation of cloud point. After the centrifugation, the tubes were kept in an
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ice bath for 10 min to increase the viscosity of the surfactant-rich phase, so
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the aqueous phase was removed by decantation. For spectrophotometric measurements, the remaining surfactant-rich phase was dissolved in 0.5 mL methanol and the absorbance of the solution was measured at 500 nm. The blank solution was submitted to the same procedure. For ICP-OES measurements, the preceding procedure was elaborated for 40 μg L-1 Ti(IV) and the surfactant-rich phase was dissolved in 0.5 mL of acidified methanol solution with HNO3 (5: 1). The extraction efficiency E (%) of Ti(IV) into the surfactant-rich phase was calculated from the following equation.
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ACCEPTED MANUSCRIPT X 100 and
are the concentration of the metal in the solution
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Where
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before the separation and that remained in the aqueous phase after phase
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separation, respectively.
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2.4 Digestion of samples
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2.4.1. Geological samples
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The real geological samples; black sand (Mediterranean Coast,
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Egypt), wadi deposits (Marsa Alam, Egypt), clay 1 (El-Sheikh Fadl, El-
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Minya Governorate, Egypt) and clay 2 (Gebel Qarara, El-Minya Governorate, Egypt) were delivered from Geology Department, Faculty of Science, Mansoura University. After crushing, the powdered samples were dried at 100 °C for 2 h. 0.20 g of each sample was transferred into a Teflon cup. For the decomposition, 5 mL of aqua regia were introduced and the mixture was slowly heated to near dryness. This step was repeated twice using another 5 mL of aqua regia every time. The residue was then dissolved in 5 mL concentrated hydrofluoric acid and the solution was heated to almost dryness. 2 mL concentrated sulphuric acid were added dropwise and heated to volatilize excess hydrofluoric acid. The dissolved samples were
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ACCEPTED MANUSCRIPT diluted with double distilled water to 100 mL in a volumetric flask. Work
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solutions used were prepared by appropriate dilution.
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2.4.2. Water samples
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It was reported that Ti species present in natural water is mainly in the form of TiO2 [29]. A preliminary digestion of samples is required to convert Ti
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species into free Ti(IV) ions suitable for reaction with ARS-CTAB prior to
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cloud point formation.
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Tap, river, sea and mineral water samples from different locations in
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Egypt were filtered using a 0.45 μm pore size membrane filter to remove the suspended solids. For the digestion [30], 20 mL of each sample were transferred into a porcelain crucible and dried at 70 ºC until evaporation. After evaporation, 1 g of potassium peroxodisulfate (K2S2O8) was added and the mixture was fused using a Bunsen burner for 15 min or until the fumes were ceased. The residue was then dissolved by adding 10 mL of 0.1 mol L−1 HNO3 and stirring on a hot plate at approximately 90 ºC for at least 5 min. The solution of each sample was diluted to 25mL with 0.1 mol L−1 HNO3.
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ACCEPTED MANUSCRIPT 2.5. Procedure for pre-concentration of Ti(IV) from real samples, simulated
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reference materials and synthetic mixtures Adequate volumes of geological, water, simulated reference materials
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and synthetic mixtures samples were transferred to 50 mL centrifuge tubes and 2 mL of the masking mixture were added. The recommended procedure
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was applied for the cloud point separation and determination of Ti(IV) as
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3.1. Effect of pH
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3. Results and discussions
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described above.
Since the pH is the most critical factor regulating metal complex formation and subsequent extraction, it was the first variable optimized in the extraction procedure. The effect of the pH on Ti(IV) extraction was assessed by varying the pH from 2 to 6. The results represented in Figure1indicated that optimal extraction efficiency is verified in the pH range 2.5 - 4. A pH of 3 was selected throughout this work.
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ACCEPTED MANUSCRIPT 3.2. Effect of ARS concentration
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ARS is a complexing agent widely used for separation, preconcentration and determination of various metal ions in different samples
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[27, 31, 32]. The presence of a quinoid oxygen, with two hydroxyl groups in ARS, makes it very suitable for chelation. The type of coordination atoms
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depends mainly on the pH of solution [33]. The presence of sulphonate
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group in the ARS moiety increases the hydrophilic character of the formed chelates. So for the formation of cloud point, it is necessary to use mixed
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micelle mediated.
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The extraction efficiency of 40 μg L-1 Ti(IV) as a function of the
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complexing agent concentration was studied in the range of 2.0×10−5 2.0×10−4 mol L−1 keeping other experimental parameters constant. As shown in Figure 2, the extraction efficiency increased by increasing ARS concentration up to 1.0×10−4 mol L−1. A concentration of 1.0×10−4 mol L−1 ARS was chosen as the optimum.
3.3. Effect of the Ionic surfactant concentration Mixed micelle formation depends on the cationic and nonionic surfactant concentrations and on the balance between these factors. It seems that the cationic surfactant CTAB reacts with ARS through the sulphonate 12
ACCEPTED MANUSCRIPT group to produce neutral (ARS–CTAB) chelating agent. On addition of Ti(IV), the sufficiently hydrophobic (Ti(IV)–ARS–CTAB) complex was
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easily isolated in the surface-rich phase of a micellar solution. Furthermore,
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the addition of a cationic surfactant CTAB is believed to be useful for
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decreasing the CMC of Triton X-114 and the possibility of resolubilisation
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of the surfactant-rich phase during the centrifugation process. The extraction efficiency was studied in different CTAB concentration range of 2.0×10−5 -
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2.0×10−4 mol L−1 (Figure 3). It was observed that the extraction efficiency
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increased by increasing CTAB concentration up to 1.0×10−4 mol L−1.
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Therefore, this concentration was selected as the optimum concentration of
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CTAB throughout the work.
3.4. Effect of the non-Ionic surfactant concentration The choice of Triton X-114 was due to its low cloud-point temperature (30 ºC), high density of the surfactant rich phase and lower toxicity at concentrations used in the range of most sensitive determinations [34]. The amount of Triton X-114 concentration also plays an important role not only in the extraction efficiency, but also the volume of surfactant-rich phase. The variation of the extraction efficiency as a function of the concentration of Triton X-114 in the range of 0.025 - 0.3% (w/v) was 13
ACCEPTED MANUSCRIPT studied. Figure 4 shows that, there is a narrow concentration range from (0.075 - 0.1% (w/v)) within which maximum extraction efficiency is
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obtained. Working outside this optimum range may decrease the extraction
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efficiency and lowers the pre-concentration factor value. Therefore, in order
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to achieve a good pre-concentration factor and high extraction efficiency, a
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concentration of 0.1 %( w/v) Triton X-114 was chosen.
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3.5 Effect of electrolytes on cloud point temperature and the extraction
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efficiency
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It was early reported that the addition of electrolytes can markedly
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facilitate the phase separation process and decrease the cloud point temperature (salting-out effect) [26, 35]. Accordingly, the effects of different salts such as (KI, KNO3, KCl and Na2SO4) were investigated in the concentration range from (0.1 - 1 mol L-1) with the goal of obtaining lower cloud point temperatures. It was noticed that the separation of cloud point occurs only in the presence of the studied electrolytes. Further the addition of Na2SO4 provides the highest efficiency for Ti(IV) separation at room temperature (25ºC), also it is obvious that the extraction efficiency is increased with increasing Na2SO4 concentration reaching maximum at
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ACCEPTED MANUSCRIPT concentration of 0.1 mol L-1. Consequently, concentration of 0.1 mol L-1 Na2SO4 was selected for further experiments.
separation
of
surfactant-rich
phase
was
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The
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3.6 Effect of centrifugation time
achieved
by
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centrifugation. The effect of centrifugation time upon the extraction
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efficiency was studied in the range of 5 - 25 min at 3500 rpm. It was founded that complete separation of the surfactant-rich phase takes place
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after 10 min. So this time was selected as the optimum centrifugation time.
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3.7 Selectivity of the proposed procedure
and
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Under the optimized conditions for CPE, the effect of different cations anions
on
the
determination
of
Ti(IV)
was
studied
by
spectrophotometrically at wavelength of 500 nm. To perform this study, 50 mL of a solution containing (50 μg L-1) of Ti(IV) and different concentrations of foreign ions were subjected to the recommended procedure and the E (%) was noticed. The tolerance limit was taken to be the amount of added ion that caused a deviation greater than ±5% in the E (%).The study is directed to improve the selectivity of the proposed procedure by studying the effect of pH and use of masking agents on the interference caused by different ions. 15
ACCEPTED MANUSCRIPT In spite of the ability of ARS-CTAB to form complexes with many lanthanides and transition metal ions, it was noticed that the formation of
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these complexes is pH dependent. Fortunately, the stable complex formed
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between Ti(IV) and ARS-CTAB is formed at pH 3 where most of studied
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interfering cations don’t form complexes with ARS-CTAB. Thus, 2000 fold
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Mn2+, Cd2+, Hg2+, Fe2+, Ni2+, Co2+, Zn2+, Pb2+, Cr3+ and 500 fold La3+, Sm3+, Nd3+, Y3+, Gd3+ ions show no significant interferences.
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Coexisting ions such as Fe3+, UO22+, Cu2+, Al3+, Zr4+and Hf4+ cause
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interference. Reduction of Fe3+ with ascorbic acid reveals high selectivity of
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the proposed procedure. In presence of ascorbic acid 2000 fold excess of
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Fe3+ don’t interfere. Further, the interference of 500 fold UO22+, Al3+ and 200 fold Zr4+, Hf4+ were eliminated using NaH2PO4. The interference of 2000 fold Cu2+ was tolerated using thiourea. Anions such as oxalate and citrate prevent the formation of Ti(IV)– ARS–CTAB complex when present in a 50 fold excess. The results shown in table 3 demonstrated that the developed procedure merit be applied for selective separation, pre-concentration and determination of Ti(IV) in real samples with high accuracy and precision.
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ACCEPTED MANUSCRIPT 3.8 Analytical figures of merit Table 4 summarizes the analytical figures of merit of the proposed
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procedure. The limit of detection (LOD) and limit of quantification (LOQ)
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were estimated as CLOD = 3SB/m and CLOQ= 10SB/m (where SB was obtained
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from the standard deviation for 10 replicate measurements of a blank
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solution and m is the slope of the calibration graph. The pre-concentration factor (PF), estimated as the concentration ratio of the analyte in the final
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diluted surfactant-rich and in the initial solution was 100. The enrichment
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factor (EF) estimated as the ratio of the slope of the calibration graph
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obtained after pre-concentration procedure with CPE to the slope of
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calibration graph without CPE. The precision of the method, calculated as the relative standard deviation (RSD) of 10 replicate measurements of 40 μg L-1 of Ti(IV).
Table 5 compares the analytical figures of merit of the proposed method with other procedures previously reported in literature.
3.9 Analytical application of the proposed procedure The accuracy of the proposed method was investigated through the recovery experiments in several synthetic mixtures (Table 6).The results obtained indicate that the recovery is in the range of 97–103.50%, which 17
ACCEPTED MANUSCRIPT reflects high accuracy of the procedure for pre-concentration and determination of Ti(IV).
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To validate the proposed procedure, a set of experiments were
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elaborated to determine Ti(IV) in four real geological samples (Table 7)
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beside spiked, non-spiked water samples (Table 8) and simulated reference
MME
and
subsequent
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materials (Table 9). Results showed that the pre-concentration by mixeddetermination
by
ICP-OES
and
visible
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spectrophotometry is accurate for Ti(IV) determination with recovery higher
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than 95%. The data of geological samples were compared with those
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obtained by solid XRF analysis (Tables 7). Statistical treatment of these data
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applying t-test and F-test approaches of the 95% confidence level and n=5 indicated that calculated values are less than tabulated values reveling that there is no significance difference between the two standard deviations at 95% confidence level for both procedures.
Conclusions The proposed procedure is simple, rapid and selective for separation and pre-concentration of Ti(IV) prior to its determination using spectral methods. The advantages of the proposed procedure includes low detection limit, very good sensitivity and high extraction efficiency, precision and pre18
ACCEPTED MANUSCRIPT concentration factor making it suitable for the trace analysis of Ti(IV). Furthermore, under optimum working conditions the interference of
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encountered matrix components highly tolerated and the procedure is proved
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to be highly selective for Ti(IV). Worth mentioning that the measurement
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using simple visible spectrophotometry could be applied when Ti(IV) is
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present in concentration (>10 µg L-1), while the use of ICP-OES for determination of lower trace concentration of Ti(IV) is recommended. In
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addition, the application of the proposed procedure for pre-concentration of to be rapid and
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Ti(IV) from water and geological samples is proved
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selective enough to tolerate matrix effect.
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[24] P. Anastas and N. Eghbali, Green chemistry: principles and Practice, Chem. Soc. Rev. 39 (2010) 301–312. [25] M. Ezoddin, F. Shemirani, R. Khani, Application of mixed-micelle cloud point extraction for speciation analysis of chromium in water samples by electrothermal atomic absorption spectrometry, Desalination 262 (2010) 183–187. [26] C.C Nascentes, M.A.Z. Arruda, Cloud point formation based on mixed micelles in the presence of electrolytes for cobalt extraction and preconcentration, Talanta 61 (2003) 759–768.
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ACCEPTED MANUSCRIPT [27] W.I. Mortada, A.A.Z. Ali, M.M. Hassanien, Mixed micelle-mediated extraction of alizarin red S complexes of Zr(IV) and Hf(IV) ions prior to
RI
spectrometry, Anal. Methods 5 (2013) 5234–5240.
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their determination by inductively coupled plasma-optical emission
SC
[28] J.C.A. de Wuilloud, R.G. Wuilloud, BB. M. Sadi, J. A. Caruso, Trace
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humic and fulvic acid determination in natural water by cloud point extraction/preconcentration using non-ionic and cationic surfactants with FI-
MA
UV detection, Analyst 128 (2003) 453–458.
D
[29] R.N.M.J. Páscoa, I.V. Tóth, A.A. Almeida, A.O.S.S. Rangel,
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Spectrophotometric sensor system based on a liquid waveguide capillary cell
AC CE P
for the determination of titanium: Application to natural waters, sunscreens and a lake sediment, Sens. Actuators B: Chem. 157 (2011) 51– 56 [30] D. Sánchez-Quiles, A. Tovar-Sánchez, B. Horstkotte, Titanium determination by multi syringe flow injection analysis system and a liquid waveguide capillary cell in solid and liquid environmental samples, Mar. Pollut. Bull. 76 (2013) 89–94. [31] M.S. Bispo, M.G.A. Korn, E.S da Boa Morte, L.S.G. Teixeira, Determination of lead in seawater by inductively coupled plasma optical emission
spectrometry
after
separation
24
and
preconcentration
with
ACCEPTED MANUSCRIPT cocrystallized naphthalene alizarin, Spectrochim. Acta Part B 57 (2002) 2175–2180.
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[32] N. Ș atıroğlu, Ç. Arpa, Cloud point extraction for the determination of
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Microchim. Acta 162 (2008) 107–112.
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trace copper in water samples by flame atomic absorption spectrometry,
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[33] L. Yadav, S.S. Sanjay, P. Ankit, M.C. Chattopadhyaya, Simultaneous determination of Stability Constant and Molar Absorptivity Coefficient of
MA
the Charge-transfer complexes of Metal–Alizarin Red S, Der pharma chem.
D
2 (2010) 114-121.
preconcentration
and
simultaneous
spectrophotometric
AC CE P
extraction,
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[34] A. Safavi, H. Abdollahi, M.R.H. Nezhad, R. Kamali, Cloud point
determination of nickel and cobalt in water samples, Spectrochim. Acta, Part A 60 (2004) 2897–2901.
[35] L. Marszall, Effect of aromatic hydrotropic agents on the cloud point of mixed ionic-nonionic surfactant solutions, Langmuir 6 (1990) 347–350.
25
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ACCEPTED MANUSCRIPT
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Scheme 1. Structure of Alizarin red S.
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110 100
D
90
TE
80
60
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E(%)
70
50 40 30 20
2
3
4
5
6
pH
Figure 1. Effect of the pH on the E(%) of Ti(IV). Conditions: 40 μg L-1 Ti (IV); 1.0×10−4 mol L−1 ARS; 0.1 mol L-1 Na2SO4; 0.1% w/v Triton X-114; 1.0×10−4 mol L−1 CTAB; centrifuge time 10 min.
26
ACCEPTED MANUSCRIPT
PT
100
RI
60
SC
E(%)
80
NU
40
0.05
0.10
0.15
0.20
D
0 0.00
MA
20
TE
ARS mmol L-1
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Figure 2. Effect of the ARS concentration on the E (%) of Ti(IV). Conditions: 40 μg L-1 Ti (IV); pH 3; 0.1 mol L-1 Na2SO4; 0.1% w/v Triton X114; 1.0×10−4 mol L−1 CTAB; centrifuge time 10 min.
27
ACCEPTED MANUSCRIPT
PT
100
RI
80
SC
E(%)
90
NU
70
D
0.05
TE
50 0.00
MA
60
0.10
0.15
0.20
CTAB mmol L-1
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Figure 3. Effect of the CTAB concentration on the E (%) of Ti(IV). Conditions: 40 μg/L Ti(IV); pH 3; 0.1 mol L-1 Na2SO4; 0.1% w/v Triton X114; 1.0×10−4 mol L−1 ARS; centrifuge time 10 min.
28
ACCEPTED MANUSCRIPT
110
PT
100
RI
90
SC
70
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E(%)
80
MA
60 50
0.10
D
0.05
TE
40 0.00
0.15
0.20
0.25
0.30
Triton X-114 (w/v)
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Figure 4. Effect of the Triton X-114 concentration )w/v( on the E (%) of Ti(IV). Conditions: 40 μg L-1 Ti(IV); pH 3; 0.1 mol L-1 Na2SO4; 1.0×10−4 mol L−1 CTAB; 1.0×10−4 mol L−1 ARS; centrifuge time 10 min.
29
ACCEPTED MANUSCRIPT Table 1. Operation parameters for determination of Ti (IV) by ICP-OES.
1350
PT
RF generator power(W) Plasma gas flow rate (L min-1)
15
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Auxiliary gas flow rate (L min-1)
0.2
SC
Nebulizer gas flow rate (L min-1)
Delay time (s) Integration time (s)
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Sample uptake rate (mL min-1)
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Pump rate (mL min-1)
0.45 2.5 2.5 7 3 1.5
The number of measurements
3
Wavelength (nm)
Ti 334.940
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TE
D
Sample loop volume (mL)
30
ACCEPTED MANUSCRIPT
Clay 1 (%)
Clay 2 (%)
TiO2
1.014
0.31
1.15
44.388
Fe2O3 tot
14.503
53.54
7.15
51.097
MgO
6.493
1.99
1.61
0.590
Na2O
1.835
0.28
1.32
0.043
Al2O3
14.222
6.34
13.45
0.376
SiO2
49.629
16.7
61.7
1.128
P2O5
0.244
0.45
0.2
0.046
SO3
0.157
-
-
0.016
K2O
1.962
0.21
2
0.020
CaO
6.323
0.91
0.51
0.346
Cr2O3
0.064
0.007
0.013
0.269
0.264
0.65
0.06
1.484
0.082
-
-
0.053
MnO
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NiO
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Component
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Wadi deposits (%)
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Table 2. Composition of real geological samples (%) with XRF analysis.
Black sand (%)
CuO
0.022
-
-
-
ZnO
0.03
-
-
0.041
SrO
0.043
-
-
0.002
ZrO2
0.045
-
-
0.064
Y2O3
.012
-
-
-
LOI
3
18.5
10.6
-
31
ACCEPTED MANUSCRIPT Table 3. Tolerance ratios of diverse ions on pre-concentration and determination of 50 μg L-1of Ti(IV) under optimum conditions. Tolerance ratio
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Foreign ions
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Na+, K+, Li+, NH4+, Mg2+, Ca2+,Sr2+, Ba2+, Cl-, I-, NO3-
5000
SC
, SO42 -, thiocyanate, thiourea, thiosulphate, acetate
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Ascorbic acid
Mn2+, Cd2 +, Hg2+, Fe2+, Ni2+, Co2+, Zn2+, Pb2+, Cr3+, b
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Fe3+ a, Cu2+
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La3+,Sm3+,Nd3+,Y3+,Gd3+, UO22+ c, Al3+
c
Citrate, oxalate a
Using ascorbic acid.
b
Using thiourea.
c
Using NaH2PO4.
500
200
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Zr4+ c, Hf4+
2000
450
TE
PO43-, F-
c
2800
50
32
ACCEPTED MANUSCRIPT Table 4. Analytical figures of merit. Parameter
Analytical feature
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ICP-OES (Spectrophotometry)
Linear range (μg L-1)
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0.3-80 (7-200)
Correlation coefficient (R2)
SC
0.9983 (.9962)
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LOD (μg L-1) LOQ (μg L-1)
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Pre-concentration factor
D
Enrichment factor
0.33 (7.67) 100 (100) 97 (80) 2.63(1.96)
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TE
R.S.D %
0.1 (2.3)
33
ACCEPTED MANUSCRIPT Table 5. Comparison of the proposed CPE procedure with other published
morin
technique
(μg L-1)
FAAS
2.9
as
complexing agent and Triton X-114 as surfactant. Solid phase extraction on 2-
ICP-MS
MCI
0.11
GEL
spectrophotometry
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nanometer size ZrO2.
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Solid phase extraction with
Linearity
Samples
References
20 (PF)
0.02-2.0 μg mL-1
Water and plant
[16]
samples
—
Water
[8]
samples
D
CHP20P resin.
61 (PF)
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nitroso-1-naphthol impregnated
EF
SC
using
LOD
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CPE
Detection
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Method
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methods in literature for separation and determination of Ti(IV).
0.1
100
—
Water
[9]
samples
Solid phase extraction with activated carbon. .
ICP-OES
0.01
80
—
Seawater samples
[10]
spectrophotometry
0.4
—
0-1 μg mL-1
Silicate rocks
[14]
ICP-OES
0.1
97,
0.3-80 μg L-1
Water, geological
Present
samples and
work
Micelle mediated extraction into benzene or toluene. CPE
using
ARS
as
complexing agent and mixed surfactant (CTAB and Triton
100(PF)
X-114) in presence of Na2SO4
synthetic mixtures
at room temperature.
FAAS: flame atomic absorption spectrometry, ICP-MS: inductively coupled plasma mass spectrometry. 34
ACCEPTED MANUSCRIPT Table 6. Recovery of 20 µg L-1 Ti(IV) in synthesized mixtures in presence of 100 µg L-1 of interfering ion and using the masking mixture by the
100.90
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Fe(III), Al(III), Sr(II), Cd(II)
D
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Fe(III), Zr(IV), Cr(III), Co(II)
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Fe(III),Gd(III), UO2(II), La(III) *
20.18 .94
SC
Fe(III), Cu(II), Zn(II), Mg(II)
Fe(III), Mn(II), Ni(II), Hg(II)
E (%)
Ti(IV) found (µg L-1) *
Synthetic mixtures
Fe(III), Sm(III), Nd(III), Y(III)
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recommended procedure.
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The results are the mean of five measurements
35
20.45
102.25
19.76
98.80
20.68
103.40
19.41
97.05
20.54
102.70
standard deviation.
ACCEPTED MANUSCRIPT Table 7. Analytical results of TiO2 analysis in geological samples.
ICP-OES*
critical=2.57
critical=7.146
Spectrophotometry*
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XRF
F5,5-testiii
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TiO2 (wt %)i
Samples
t-testii
1.014
1.034
025 (2.42)
1.022
022 (2.12)
1.79
1.29
Clay 1
0.310
0.317
011(3.47)
0.307
01 (3.26)
1.42
1.21
Clay 2
1.150
1.168 0.032(2.74 )
1.144 0.04(3.50)
1.26
1.56
Black sand
44.388
44.906
1.10
1.15
*
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(2.34)
SC
Wadi deposits
45.066
i
t-test between XRF and ICP-OES measurements. F- test between ICP-OES and spectrophotometry measurements.
AC CE P
iii
TE
D
ii
TiO2 was determined from Ti(IV).
standard deviation (R.S.D %).
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The results are the mean of five measurements
(2.49)
36
ACCEPTED MANUSCRIPT Table 8. Analytical results of Ti(IV) determination in water samples. Ti(IV) µg L-1 Added
Found*
E (%)
Tap water
0
N.D
-
RI
PT
sample
5
SC
5.08
10
NU
9.85
102.2
11.10
100.3
0
3.55
-
5
8.52
99.4
10
13.69
101.4
MA D TE
98.5
6.18
10
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15
-
0 5
Mineral water
101.6
1.07
Sea water
River water
09
0
N.D
-
5
4.88
97.6
10
9.96
99.6
N.D : not detectable. *
The results are the mean of five measurements
37
standard deviation.
ACCEPTED MANUSCRIPT Table 9. Analytical results of Ti(IV) determination in simulated reference
PT
materials.
Ti (IV) found (wt %)*
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Samples
Simulated NKK CRM No. 920
0.153
006
Simulated NKK CRM No. 1021
0.041
MA
(Al, Si, Cu, Zn, alloy) b
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(Al alloy) a
*
Spectrophotometry
SC
ICP-OES
The results are the mean of five measurements
a
0.149
008
0.039
standard deviation
D
Si, 0.78; Fe, 0.729; Mg, 0.46; Cr, 0.27; Bi, 0.06; Ga, 0.05; Ca, 0.03; Co,
Si, 5.56; Fe, 0.99; Mg, 0.29; Cr, 0.03; Sn, 0.10; Pb, 0.18; Sb, 0.01; Zr, 0.01;
AC CE P
b
TE
0.10; Ni, 0.29; V, 0.15; Cu, 0.71; Mn, 0.20, Zn, 0.80; Ti, 0.15
Bi, 0.01; V, 0.007; Ca, 0.004; Mn, 0.11; Ni, 0.14; Cu, 2.72, Zn, 1.76; Ti, 0.04
38
ACCEPTED MANUSCRIPT Figure captions Scheme 1. Structure of Alizarin red S.
PT
Figure 1. Effect of the pH on the E(%) of Ti(IV). Conditions: 40 μg L-1 Ti
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(IV); 1.0×10−4 mol L−1 ARS; 0.1 mol L-1 Na2SO4; 0.1% w/v Triton X-114;
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1.0×10−4 mol L−1 CTAB; centrifuge time 10 min.
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Figure 2. Effect of the ARS concentration on the E (%) of Ti(IV). Conditions: 40 μg L-1 Ti (IV); pH 3; 0.1 mol L-1 Na2SO4; 0.1% w/v Triton X-
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114; 1.0×10−4 mol L−1 CTAB; centrifuge time 10 min.
D
Figure 3. Effect of the CTAB concentration on the E (%) of Ti(IV).
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Conditions: 40 μg/L Ti(IV); pH 3; 0.1 mol L-1 Na2SO4; 0.1% w/v Triton X-
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114; 1.0×10−4 mol L−1 ARS; centrifuge time 10 min. Figure 4. Effect of the Triton X-114 concentration )w/v( on the E (%) of Ti(IV). Conditions: 40 μg L-1 Ti(IV); pH 3; 0.1 mol L-1 Na2SO4; 1.0×10−4 mol L−1 CTAB; 1.0×10−4 mol L−1 ARS; centrifuge time 10 min.
39
ACCEPTED MANUSCRIPT Highlights:
AC CE P
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SC
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PT
A CPE procedure for selective Ti(IV) enrichment from different matrices is proposed. The analytical parameters indicate the high validation of the procedure. The procedure is applied for determination of Ti(IV) in geological and water samples.
40
S0026-265X(15)00175-7 doi: 10.1016/j.microc.2015.08.003 MICROC 2204
To appear in:
Microchemical Journal
Received date: Revised date: Accepted date:
23 June 2015 2 August 2015 10 August 2015
Please cite this article as: Ibrahim M.M. Kenawy, Magdi E. Khalifa, Mohamed M. Hassanien, Mohamed M. Elnagar, Application of mixed micelle-mediated extraction for selective separation and determination of Ti(IV) in geological and water samples, Microchemical Journal (2015), doi: 10.1016/j.microc.2015.08.003
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Application of mixed micelle-mediated extraction for selective
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separation and determination of Ti(IV) in geological and water
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samples
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Ibrahim M.M.Kenawya, Magdi E. Khalifaa, Mohamed M. Hassanienb,
Chemistry Department, Faculty of Science, Mansoura University,
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a
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Mohamed M. Elnagara*
Mansoura, Egypt Chemistry Department, Industrial Education College, Beni-Suef
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b
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University, Beni-Suef, Egypt
ABSTRACT
A simple cloud point extraction (CPE) methodology based on the complexation
of
Ti(IV)
with
Alizarin
Red
S
(ARS)
and
cetyltrimethylammonium bromide (CTAB) at pH 3 followed by extraction with Triton X-114 in presence of Na2SO4 at room temperature (25 ºC) has been developed. The enriched analyte in the surfactant rich phase was determined by visible spectrophotometry or inductively coupled plasma optical emission spectrometry (ICP-OES). The main factors affecting mixed micelle-mediated extraction efficiency were studied. At optimum conditions, 1
ACCEPTED MANUSCRIPT the linear range of 0.3-80 and 7-200 μg L-1 with a detection limit of 0.1 and 2.3 μg L-1 were obtained for separation and determination of Ti(IV) with 50
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mL solution using ICP-OES and visible spectrophotometry, respectively. A
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pre-concentration factor of 100 was achieved for both techniques. The effect
SC
of diverse cations and anions on the extraction efficiency was tested. At
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optimum pH, the separation is proved to be highly selective for Ti(IV), since the extraction of many lanthanide and transition metal alizarinate complexes
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using Triton X-114 occurs at different pH ranges. The interference of 2000
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fold excess of Fe3+ is tolerated using ascorbic acid as a masking agent. Also,
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NaH2PO4 is used to eliminate the interference caused by UO22+, Zr4+, Hf4+
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and Al3+. The accuracy of the procedure was evaluated through recovery experiments on synthetic mixtures. The proposed procedure has been successfully applied for separation and determination of Ti(IV) in geological samples, simulated reference materials and water samples with satisfactory results.
Key words: Titanium; Mixed micelle-mediated extraction; Alizarin red S; Geological samples; Water samples *
To whom all correspondence should be addressed
E-mail: [email protected] 2
ACCEPTED MANUSCRIPT 1. Introduction Titanium (Ti) and its alloys have extensively numerous high-
PT
technological industrial applications due to their excellent characteristics
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such as high specific strength-to-weight ratio, high specific modulus, good
SC
oxidation and superior corrosion resistance [1]. In particular, Ti has been
NU
widely used in catalysis, paint pigments, rubber, textiles, and plastics [2]. The excellent corrosion resistance of Ti allows this material to be used in
MA
solar energy cells and as a tube material for heat exchangers or condensers in
D
nuclear power plants [3, 4]. It is a valuable alloying agent and coexists in a
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number of industrially important alloys which are used principally in guided
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missiles, high-speed aircrafts, rockets, marine components and filament material in electrical applications [2]. Also, the medical application of TiO2 nanoparticles shows great promising data for potential uses as disinfectants [5], diagnostic assays [6], and tumor cell killing agents [7]. The determination of Ti(IV) in different samples has attracted considerable interest. However, direct determination of trace level of Ti in real samples by instrumental techniques is still notably difficult. The low concentration of Ti(IV) and the high complexity of the sample matrices are the main problems. Consequently, the application of separation and preconcentration techniques is of special interest in such cases. Among these, 3
ACCEPTED MANUSCRIPT solid phase extraction [8-11], ion-exchanger [12] liquid-liquid extraction [13-15] and cloud point extraction [16] were reported.
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The application of cloud point extraction (CPE) for the separation and
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pre-concentration of different metal ions [17-19], biomaterials [20] and
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organic compounds [21, 22] is of special interest. CPE technique is based on
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the property of most non-ionic surfactants to form micelles and become turbid in aqueous solution. On heating above critical temperature called
MA
cloud-point temperature (CPT) or by the adding of salting-out electrolytes,
D
the micellar solution separates into two phases: (i) a surfactant-rich phase, in
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which the analyte ions could be pre-concentrated, and (ii) an aqueous phase
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containing surfactant at a concentration near to a critical micelle concentration (CMC). CPE has several advantages such as the separation using mild conditions, the ability to concentrate a variety of analytes with near complete recovery, speed, sensitivity, low cost and high preconcentration factors [23]. Moreover, it complies with the principles of green chemistry because of its lower toxicity to the environment than extractions that use organic solvents [24]. In this manner mixed micellemediated extraction (mixed-MME) system is becoming an important for separation and pre-concentration of many metal ions [25-27]. The use of cationic surfactants in combination with a non-ionic surfactant exhibits 4
ACCEPTED MANUSCRIPT synergism compared to a single surfactant due to higher surface activity. Moreover, the interaction of ionic surfactant with a charged complex leads
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to formation of neutral molecules which could be extracted by non-ionic
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surfactant [26, 28].
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The aim of the work was to develop a new CPE procedure for
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selective separation and pre-concentration of Ti(IV) from the commonly encountered matrix components prior to its determination using ICP-OES or
MA
visible spectrophotometry. The procedure is based on the complexation of
D
Ti(IV) with Alizarin Red S (ARS) (Scheme 1) and the ionic surfactant
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cetyltrimethylammonium bromide (CTAB) at pH 3 followed by extraction
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with Triton X-114 (non ionic surfactant) in presence of Na2SO4. The factors affecting the efficiency of the procedure were systematically studied and optimized. At optimum conditions, the proposed procedure was applied for separation, pre-concentration and determination of Ti(IV) in water samples, simulated reference materials, synthetic mixtures and real geological samples.
5
ACCEPTED MANUSCRIPT 2. Experimental 2.1. Instrumentation
PT
A Perkin Elmer Inductively Coupled Plasma-Optical Emission
RI
Spectrometry (ICP- OES, Optima 8300, USA) was used for the
SC
determination of Ti(IV). The optimum operation conditions for the ICP-OES
NU
instrument were summarized in Table 1. XRF analysis of real geological samples (wadi deposits, clay 1, clay 2 and black sand) (Table 2.) was
MA
performed with a PANalytical Axios Advanced XRF. A Unicam UV/Vis
D
spectrometer UV2 with 1-cm quartz cell (1 mL) was used for recording
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absorption spectra in the range 400-700 nm. The pH values were adjusted
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using a Hanna instrument model 8519 pH meter (Hanna instruments, Germany) furnished with a combined glass-saturated calomel electrode. A thermostatic water bath maintained at desired temperature was used for cloud point experiments. A CH90-2 centrifuge (Hinotek Technology Co. Ltd., China) was used to speed up the phase separation.
2.2. Reagents, solutions Otherwise specified, all reagents used were of analytical reagent grade. Aqueous solutions were prepared with double distilled water. All glassware used for trace analysis were kept in 10 % (w/v) nitric acid at least 6
ACCEPTED MANUSCRIPT for 24 h and subsequently washed four times with double distilled water before use. Stock standard solution of titanium at a concentration of 1000 μg
PT
mL-1 was obtained from Spectrosol (BDH, England). The working standard
RI
solutions were freshly prepared by appropriate dilution of the stock standard
SC
solutions. A 5×10−3 mol L−1 solution of ARS was prepared by dissolving 1.8
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g of sodium alizarin sulphonate (Merck, Germany) in double distilled water and diluting to 1000 mL. The surfactants, Triton X-114 (obtained from
MA
Sigma-Aldrich, USA) and CTAB (Acros Chemicals, Ottawa, ON, Canada)
D
were used without further purification. Appropriate concentrations of
TE
interfering ions were prepared by dissolving their nitrate salts in double
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distilled water. The pH of solutions were adjusted using hydrochloric acid– sodium acetate 1 mol L−1 (pH 1.0 - 2.5) and acetic acid–sodium acetate 0.2 mol L−1 (pH 3.0 –7.0) buffer solutions. A masking mixture was prepared by mixing equal volumes of (0.05 mol L−1 ascorbic acid, 5×10−3 NaH2PO4 and 0.05 mol L−1 thiourea) to be used for analysis of real samples, simulated reference material and synthetic mixtures.
7
ACCEPTED MANUSCRIPT 2.3 Recommended procedure of mixed-MME
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In a 50 mL centrifuge tube, an aliquot of Ti(IV) standard solution was mixed with 1 mL of 5×10−3 mol L−1 ARS, 1 mL of 5×10−3 mol L−1 CTAB, 5
SC
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ml of 1 mol L−1 Na2SO4 and 5 ml the of acetate buffer (pH 3). Then, 2.5 mL of (2 % w/v) Triton X-114 were added and final volume of micellar solution
NU
is brought up to 50 mL using double distilled water. The solution is then
MA
stirred at room temperature (25ºC) until it began to be turbid. Finally, this solution was centrifuged at 3500 rpm for 10 min in order to facilitate the
D
separation of cloud point. After the centrifugation, the tubes were kept in an
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ice bath for 10 min to increase the viscosity of the surfactant-rich phase, so
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the aqueous phase was removed by decantation. For spectrophotometric measurements, the remaining surfactant-rich phase was dissolved in 0.5 mL methanol and the absorbance of the solution was measured at 500 nm. The blank solution was submitted to the same procedure. For ICP-OES measurements, the preceding procedure was elaborated for 40 μg L-1 Ti(IV) and the surfactant-rich phase was dissolved in 0.5 mL of acidified methanol solution with HNO3 (5: 1). The extraction efficiency E (%) of Ti(IV) into the surfactant-rich phase was calculated from the following equation.
8
ACCEPTED MANUSCRIPT X 100 and
are the concentration of the metal in the solution
PT
Where
RI
before the separation and that remained in the aqueous phase after phase
SC
separation, respectively.
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2.4 Digestion of samples
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2.4.1. Geological samples
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The real geological samples; black sand (Mediterranean Coast,
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Egypt), wadi deposits (Marsa Alam, Egypt), clay 1 (El-Sheikh Fadl, El-
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Minya Governorate, Egypt) and clay 2 (Gebel Qarara, El-Minya Governorate, Egypt) were delivered from Geology Department, Faculty of Science, Mansoura University. After crushing, the powdered samples were dried at 100 °C for 2 h. 0.20 g of each sample was transferred into a Teflon cup. For the decomposition, 5 mL of aqua regia were introduced and the mixture was slowly heated to near dryness. This step was repeated twice using another 5 mL of aqua regia every time. The residue was then dissolved in 5 mL concentrated hydrofluoric acid and the solution was heated to almost dryness. 2 mL concentrated sulphuric acid were added dropwise and heated to volatilize excess hydrofluoric acid. The dissolved samples were
9
ACCEPTED MANUSCRIPT diluted with double distilled water to 100 mL in a volumetric flask. Work
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solutions used were prepared by appropriate dilution.
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2.4.2. Water samples
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It was reported that Ti species present in natural water is mainly in the form of TiO2 [29]. A preliminary digestion of samples is required to convert Ti
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species into free Ti(IV) ions suitable for reaction with ARS-CTAB prior to
D
cloud point formation.
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Tap, river, sea and mineral water samples from different locations in
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Egypt were filtered using a 0.45 μm pore size membrane filter to remove the suspended solids. For the digestion [30], 20 mL of each sample were transferred into a porcelain crucible and dried at 70 ºC until evaporation. After evaporation, 1 g of potassium peroxodisulfate (K2S2O8) was added and the mixture was fused using a Bunsen burner for 15 min or until the fumes were ceased. The residue was then dissolved by adding 10 mL of 0.1 mol L−1 HNO3 and stirring on a hot plate at approximately 90 ºC for at least 5 min. The solution of each sample was diluted to 25mL with 0.1 mol L−1 HNO3.
10
ACCEPTED MANUSCRIPT 2.5. Procedure for pre-concentration of Ti(IV) from real samples, simulated
PT
reference materials and synthetic mixtures Adequate volumes of geological, water, simulated reference materials
SC
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and synthetic mixtures samples were transferred to 50 mL centrifuge tubes and 2 mL of the masking mixture were added. The recommended procedure
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was applied for the cloud point separation and determination of Ti(IV) as
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3.1. Effect of pH
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3. Results and discussions
MA
described above.
Since the pH is the most critical factor regulating metal complex formation and subsequent extraction, it was the first variable optimized in the extraction procedure. The effect of the pH on Ti(IV) extraction was assessed by varying the pH from 2 to 6. The results represented in Figure1indicated that optimal extraction efficiency is verified in the pH range 2.5 - 4. A pH of 3 was selected throughout this work.
11
ACCEPTED MANUSCRIPT 3.2. Effect of ARS concentration
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ARS is a complexing agent widely used for separation, preconcentration and determination of various metal ions in different samples
SC
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[27, 31, 32]. The presence of a quinoid oxygen, with two hydroxyl groups in ARS, makes it very suitable for chelation. The type of coordination atoms
NU
depends mainly on the pH of solution [33]. The presence of sulphonate
MA
group in the ARS moiety increases the hydrophilic character of the formed chelates. So for the formation of cloud point, it is necessary to use mixed
D
micelle mediated.
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The extraction efficiency of 40 μg L-1 Ti(IV) as a function of the
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complexing agent concentration was studied in the range of 2.0×10−5 2.0×10−4 mol L−1 keeping other experimental parameters constant. As shown in Figure 2, the extraction efficiency increased by increasing ARS concentration up to 1.0×10−4 mol L−1. A concentration of 1.0×10−4 mol L−1 ARS was chosen as the optimum.
3.3. Effect of the Ionic surfactant concentration Mixed micelle formation depends on the cationic and nonionic surfactant concentrations and on the balance between these factors. It seems that the cationic surfactant CTAB reacts with ARS through the sulphonate 12
ACCEPTED MANUSCRIPT group to produce neutral (ARS–CTAB) chelating agent. On addition of Ti(IV), the sufficiently hydrophobic (Ti(IV)–ARS–CTAB) complex was
PT
easily isolated in the surface-rich phase of a micellar solution. Furthermore,
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the addition of a cationic surfactant CTAB is believed to be useful for
SC
decreasing the CMC of Triton X-114 and the possibility of resolubilisation
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of the surfactant-rich phase during the centrifugation process. The extraction efficiency was studied in different CTAB concentration range of 2.0×10−5 -
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2.0×10−4 mol L−1 (Figure 3). It was observed that the extraction efficiency
D
increased by increasing CTAB concentration up to 1.0×10−4 mol L−1.
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Therefore, this concentration was selected as the optimum concentration of
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CTAB throughout the work.
3.4. Effect of the non-Ionic surfactant concentration The choice of Triton X-114 was due to its low cloud-point temperature (30 ºC), high density of the surfactant rich phase and lower toxicity at concentrations used in the range of most sensitive determinations [34]. The amount of Triton X-114 concentration also plays an important role not only in the extraction efficiency, but also the volume of surfactant-rich phase. The variation of the extraction efficiency as a function of the concentration of Triton X-114 in the range of 0.025 - 0.3% (w/v) was 13
ACCEPTED MANUSCRIPT studied. Figure 4 shows that, there is a narrow concentration range from (0.075 - 0.1% (w/v)) within which maximum extraction efficiency is
PT
obtained. Working outside this optimum range may decrease the extraction
RI
efficiency and lowers the pre-concentration factor value. Therefore, in order
SC
to achieve a good pre-concentration factor and high extraction efficiency, a
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concentration of 0.1 %( w/v) Triton X-114 was chosen.
MA
3.5 Effect of electrolytes on cloud point temperature and the extraction
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efficiency
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It was early reported that the addition of electrolytes can markedly
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facilitate the phase separation process and decrease the cloud point temperature (salting-out effect) [26, 35]. Accordingly, the effects of different salts such as (KI, KNO3, KCl and Na2SO4) were investigated in the concentration range from (0.1 - 1 mol L-1) with the goal of obtaining lower cloud point temperatures. It was noticed that the separation of cloud point occurs only in the presence of the studied electrolytes. Further the addition of Na2SO4 provides the highest efficiency for Ti(IV) separation at room temperature (25ºC), also it is obvious that the extraction efficiency is increased with increasing Na2SO4 concentration reaching maximum at
14
ACCEPTED MANUSCRIPT concentration of 0.1 mol L-1. Consequently, concentration of 0.1 mol L-1 Na2SO4 was selected for further experiments.
separation
of
surfactant-rich
phase
was
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The
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3.6 Effect of centrifugation time
achieved
by
SC
centrifugation. The effect of centrifugation time upon the extraction
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efficiency was studied in the range of 5 - 25 min at 3500 rpm. It was founded that complete separation of the surfactant-rich phase takes place
D
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after 10 min. So this time was selected as the optimum centrifugation time.
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3.7 Selectivity of the proposed procedure
and
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Under the optimized conditions for CPE, the effect of different cations anions
on
the
determination
of
Ti(IV)
was
studied
by
spectrophotometrically at wavelength of 500 nm. To perform this study, 50 mL of a solution containing (50 μg L-1) of Ti(IV) and different concentrations of foreign ions were subjected to the recommended procedure and the E (%) was noticed. The tolerance limit was taken to be the amount of added ion that caused a deviation greater than ±5% in the E (%).The study is directed to improve the selectivity of the proposed procedure by studying the effect of pH and use of masking agents on the interference caused by different ions. 15
ACCEPTED MANUSCRIPT In spite of the ability of ARS-CTAB to form complexes with many lanthanides and transition metal ions, it was noticed that the formation of
PT
these complexes is pH dependent. Fortunately, the stable complex formed
RI
between Ti(IV) and ARS-CTAB is formed at pH 3 where most of studied
SC
interfering cations don’t form complexes with ARS-CTAB. Thus, 2000 fold
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Mn2+, Cd2+, Hg2+, Fe2+, Ni2+, Co2+, Zn2+, Pb2+, Cr3+ and 500 fold La3+, Sm3+, Nd3+, Y3+, Gd3+ ions show no significant interferences.
MA
Coexisting ions such as Fe3+, UO22+, Cu2+, Al3+, Zr4+and Hf4+ cause
D
interference. Reduction of Fe3+ with ascorbic acid reveals high selectivity of
TE
the proposed procedure. In presence of ascorbic acid 2000 fold excess of
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Fe3+ don’t interfere. Further, the interference of 500 fold UO22+, Al3+ and 200 fold Zr4+, Hf4+ were eliminated using NaH2PO4. The interference of 2000 fold Cu2+ was tolerated using thiourea. Anions such as oxalate and citrate prevent the formation of Ti(IV)– ARS–CTAB complex when present in a 50 fold excess. The results shown in table 3 demonstrated that the developed procedure merit be applied for selective separation, pre-concentration and determination of Ti(IV) in real samples with high accuracy and precision.
16
ACCEPTED MANUSCRIPT 3.8 Analytical figures of merit Table 4 summarizes the analytical figures of merit of the proposed
PT
procedure. The limit of detection (LOD) and limit of quantification (LOQ)
RI
were estimated as CLOD = 3SB/m and CLOQ= 10SB/m (where SB was obtained
SC
from the standard deviation for 10 replicate measurements of a blank
NU
solution and m is the slope of the calibration graph. The pre-concentration factor (PF), estimated as the concentration ratio of the analyte in the final
MA
diluted surfactant-rich and in the initial solution was 100. The enrichment
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factor (EF) estimated as the ratio of the slope of the calibration graph
TE
obtained after pre-concentration procedure with CPE to the slope of
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calibration graph without CPE. The precision of the method, calculated as the relative standard deviation (RSD) of 10 replicate measurements of 40 μg L-1 of Ti(IV).
Table 5 compares the analytical figures of merit of the proposed method with other procedures previously reported in literature.
3.9 Analytical application of the proposed procedure The accuracy of the proposed method was investigated through the recovery experiments in several synthetic mixtures (Table 6).The results obtained indicate that the recovery is in the range of 97–103.50%, which 17
ACCEPTED MANUSCRIPT reflects high accuracy of the procedure for pre-concentration and determination of Ti(IV).
PT
To validate the proposed procedure, a set of experiments were
RI
elaborated to determine Ti(IV) in four real geological samples (Table 7)
SC
beside spiked, non-spiked water samples (Table 8) and simulated reference
MME
and
subsequent
NU
materials (Table 9). Results showed that the pre-concentration by mixeddetermination
by
ICP-OES
and
visible
MA
spectrophotometry is accurate for Ti(IV) determination with recovery higher
D
than 95%. The data of geological samples were compared with those
TE
obtained by solid XRF analysis (Tables 7). Statistical treatment of these data
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applying t-test and F-test approaches of the 95% confidence level and n=5 indicated that calculated values are less than tabulated values reveling that there is no significance difference between the two standard deviations at 95% confidence level for both procedures.
Conclusions The proposed procedure is simple, rapid and selective for separation and pre-concentration of Ti(IV) prior to its determination using spectral methods. The advantages of the proposed procedure includes low detection limit, very good sensitivity and high extraction efficiency, precision and pre18
ACCEPTED MANUSCRIPT concentration factor making it suitable for the trace analysis of Ti(IV). Furthermore, under optimum working conditions the interference of
PT
encountered matrix components highly tolerated and the procedure is proved
RI
to be highly selective for Ti(IV). Worth mentioning that the measurement
SC
using simple visible spectrophotometry could be applied when Ti(IV) is
NU
present in concentration (>10 µg L-1), while the use of ICP-OES for determination of lower trace concentration of Ti(IV) is recommended. In
MA
addition, the application of the proposed procedure for pre-concentration of to be rapid and
D
Ti(IV) from water and geological samples is proved
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selective enough to tolerate matrix effect.
References
[1] I. Gurrappa, A.K. Gogia, High performance coatings for titanium alloys to protect against oxidation, Surf. Coat. Technol. 139 (2001) 216–221. [2] R.E. Krebs, The History and Use of Our Earth's Chemical Elements: A Reference Guide (2nd edition), 2006, p. 92. [3] A.N. Shipway, E. Katz, I. Willner, Nanoparticle arrays on surfaces for electronic, optical and sensor applications, Chem. Phys. Chem. 1 (2000) 18– 52.
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ACCEPTED MANUSCRIPT [4] U.K. Mudali, B.M.A. Rao, K. Shanmugam, R. Natarajan, B. Raj, Corrosion and microstructural aspects of dissimilar joints of titanium and
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type 304L stainless steel, J. Nucl. Mater. 321 (2003) 40–48.
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[5] Y.H Tsuang, J.S Sun, Y.C Huang, C.H Lu, W.H Chang, C.C Wang,
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Studies of photokilling of bacteria using titanium dioxide nanoparticles,
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Wu,
TiO2 nanoparticles
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Tseng,
detection
MA
[6]
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Artif Organs 32 (2008) 167–174.
Phosphate-modified
of dopamine,
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D
adrenaline, and catechol based on fluorescence quenching, Langmuir 23
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[7] J.W. Seo, H. Chung, M.Y. Kim, J. Lee, I.H. Choi, J. Cheon, Development of water-soluble single-crystalline TiO2 nanoparticles for photocatalytic cancer-cell treatment, Small 3 (2007) 850-853. [8] F.A. Aydin, M. Soylak, Separation, preconcentration and inductively coupled plasma-mass spectrometric (ICP-MS) determination of thorium(IV), titanium(IV), iron(III), lead(II) and chromium(III) on 2-nitroso-1-naphthol impregnated MCI GELCHP20P resin, J. Hazard. Mat. 173 (2010) 669–674. [9] F.Y. Zheng, S.X. Li, L.X. Lin, L.Q. Cheng, Simple and rapid spectrophotometric determination of trace titanium (IV) enriched by
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ACCEPTED MANUSCRIPT nanometer size zirconium dioxide in natural water, J. Hazard. Mat. 172 (2009) 618–622.
PT
[10] S.A. Rocha, S.L.C. Ferreira, A procedure of separation and
SC
OES, Eurasian J. Anal. Chem. 2 (2007) 1–11.
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preconcentration for titanium determination in seawater samples by ICP
NU
[11] M.K. Barman, B. Srivastava, M. Chatterjee, B. Mandal, Solid-phase extraction, separation and preconcentration of titanium(IV) with SSG-V10
MA
from some other toxic cations: a molecular interpretation supported by DFT,
D
RSC Adv. 4 (2014) 33923-33934.
TE
[12] T. Kiriyama, M. Haraguchi, R. Kuroda, Combined anion-exchange
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separation and spectrophotometric determination of traces of titanium in sea water, Fresenius Z. Anal. Chem. 307 (1981) 352–355. [13] V. Vojković, V. A. Živčić, V. Drušković, Spectrophotometric determination of titanium(IV) by extraction of its thiocyanate complex with cationic surfactants, Spectrosc. Lett. 37 (2004) 401–420. [14] P.K. Tarafder, R. Thakur, Micelle mediated extraction of titanium and its ultra-trace determination in silicate rocks, Talanta 75 (2008) 326–331. [15] Y.K. Agrawal, S. Sudhakar, Extractive spectrophotometric and inductively
coupled
plasma
atomic
21
emission
spectrophotometric
ACCEPTED MANUSCRIPT determination of titanium by using dibenzo-18-crown-6, Talanta 57 (2002) 97–104.
PT
[16] M. Mirzaei, A.K. Naeini, Determinaton of Trace Amounts of Titanium
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by Flame Atomic Absorption Spectrometry after Cloud Point Extraction, J.
SC
Anal. Chem. 68 (2013) 595–599.
NU
[17] C. Zeng, L. Ji, C. Zhou, F. Zhang, M. Liu, Q. Xie, Chemical vapor generation of bismuth in non-aqueous phase based on cloud point extraction
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coupled with thermospray flame furnace atomic absorption spectrometric
D
determination, Microchem. J. 119 (2015) 1–5.
TE
[18] S. S. Arain, T. G. Kazi, J. B. Arain, H. I. Afridi, K. D. Brahman,
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Naeemullah, Preconcentration of toxic elements in artificial saliva extract of different smokeless tobacco products by dual-cloud point extraction, Microchem. J. 112 (2014) 42–49. [19] I.L. García, Y.V. Martínez, M.H. Córdoba, Non-chromatographic speciation of chromium at sub-ppb levels using cloud point extraction in the presence of unmodified silver nanoparticles, Talanta 132 (2015) 23–28. [20] M. Rahimi, P. Hashemi , F. Nazari, Cold column trapping-cloud point extraction coupled to high performance liquid chromatography for preconcentration and determination of curcumin in human urine, Anal. Chim. Acta 826 (2014) 35–42. 22
ACCEPTED MANUSCRIPT [21] M. Bahram, F. Keshvari, P. Najafi-Moghaddam, Development of cloud point extraction using pH-sensitive hydrogel for preconcentration and
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determination of malachite green, Talanta 85 (2011) 891–896.
RI
[22] Z. Zhou, J. Chen, D. Zhao, M. Yang, Determination of Four Carbamate
SC
Pesticides in Corn by Cloud Point Extraction and High-Performance Liquid
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Chromatography in the Visible Region Based on Their Derivatization Reaction, J. Agric. Food Chem. 57 (2009) 8722–8727.
MA
[23] K. Pytlakowska, V. Kozik, M. Dabioch, Complex-forming organic
D
ligands in cloud-point extraction of metal ions: A review, Talanta 110
TE
(2013) 202–228.
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[24] P. Anastas and N. Eghbali, Green chemistry: principles and Practice, Chem. Soc. Rev. 39 (2010) 301–312. [25] M. Ezoddin, F. Shemirani, R. Khani, Application of mixed-micelle cloud point extraction for speciation analysis of chromium in water samples by electrothermal atomic absorption spectrometry, Desalination 262 (2010) 183–187. [26] C.C Nascentes, M.A.Z. Arruda, Cloud point formation based on mixed micelles in the presence of electrolytes for cobalt extraction and preconcentration, Talanta 61 (2003) 759–768.
23
ACCEPTED MANUSCRIPT [27] W.I. Mortada, A.A.Z. Ali, M.M. Hassanien, Mixed micelle-mediated extraction of alizarin red S complexes of Zr(IV) and Hf(IV) ions prior to
RI
spectrometry, Anal. Methods 5 (2013) 5234–5240.
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their determination by inductively coupled plasma-optical emission
SC
[28] J.C.A. de Wuilloud, R.G. Wuilloud, BB. M. Sadi, J. A. Caruso, Trace
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humic and fulvic acid determination in natural water by cloud point extraction/preconcentration using non-ionic and cationic surfactants with FI-
MA
UV detection, Analyst 128 (2003) 453–458.
D
[29] R.N.M.J. Páscoa, I.V. Tóth, A.A. Almeida, A.O.S.S. Rangel,
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Spectrophotometric sensor system based on a liquid waveguide capillary cell
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for the determination of titanium: Application to natural waters, sunscreens and a lake sediment, Sens. Actuators B: Chem. 157 (2011) 51– 56 [30] D. Sánchez-Quiles, A. Tovar-Sánchez, B. Horstkotte, Titanium determination by multi syringe flow injection analysis system and a liquid waveguide capillary cell in solid and liquid environmental samples, Mar. Pollut. Bull. 76 (2013) 89–94. [31] M.S. Bispo, M.G.A. Korn, E.S da Boa Morte, L.S.G. Teixeira, Determination of lead in seawater by inductively coupled plasma optical emission
spectrometry
after
separation
24
and
preconcentration
with
ACCEPTED MANUSCRIPT cocrystallized naphthalene alizarin, Spectrochim. Acta Part B 57 (2002) 2175–2180.
PT
[32] N. Ș atıroğlu, Ç. Arpa, Cloud point extraction for the determination of
SC
Microchim. Acta 162 (2008) 107–112.
RI
trace copper in water samples by flame atomic absorption spectrometry,
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[33] L. Yadav, S.S. Sanjay, P. Ankit, M.C. Chattopadhyaya, Simultaneous determination of Stability Constant and Molar Absorptivity Coefficient of
MA
the Charge-transfer complexes of Metal–Alizarin Red S, Der pharma chem.
D
2 (2010) 114-121.
preconcentration
and
simultaneous
spectrophotometric
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extraction,
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[34] A. Safavi, H. Abdollahi, M.R.H. Nezhad, R. Kamali, Cloud point
determination of nickel and cobalt in water samples, Spectrochim. Acta, Part A 60 (2004) 2897–2901.
[35] L. Marszall, Effect of aromatic hydrotropic agents on the cloud point of mixed ionic-nonionic surfactant solutions, Langmuir 6 (1990) 347–350.
25
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ACCEPTED MANUSCRIPT
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Scheme 1. Structure of Alizarin red S.
MA
110 100
D
90
TE
80
60
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E(%)
70
50 40 30 20
2
3
4
5
6
pH
Figure 1. Effect of the pH on the E(%) of Ti(IV). Conditions: 40 μg L-1 Ti (IV); 1.0×10−4 mol L−1 ARS; 0.1 mol L-1 Na2SO4; 0.1% w/v Triton X-114; 1.0×10−4 mol L−1 CTAB; centrifuge time 10 min.
26
ACCEPTED MANUSCRIPT
PT
100
RI
60
SC
E(%)
80
NU
40
0.05
0.10
0.15
0.20
D
0 0.00
MA
20
TE
ARS mmol L-1
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Figure 2. Effect of the ARS concentration on the E (%) of Ti(IV). Conditions: 40 μg L-1 Ti (IV); pH 3; 0.1 mol L-1 Na2SO4; 0.1% w/v Triton X114; 1.0×10−4 mol L−1 CTAB; centrifuge time 10 min.
27
ACCEPTED MANUSCRIPT
PT
100
RI
80
SC
E(%)
90
NU
70
D
0.05
TE
50 0.00
MA
60
0.10
0.15
0.20
CTAB mmol L-1
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Figure 3. Effect of the CTAB concentration on the E (%) of Ti(IV). Conditions: 40 μg/L Ti(IV); pH 3; 0.1 mol L-1 Na2SO4; 0.1% w/v Triton X114; 1.0×10−4 mol L−1 ARS; centrifuge time 10 min.
28
ACCEPTED MANUSCRIPT
110
PT
100
RI
90
SC
70
NU
E(%)
80
MA
60 50
0.10
D
0.05
TE
40 0.00
0.15
0.20
0.25
0.30
Triton X-114 (w/v)
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Figure 4. Effect of the Triton X-114 concentration )w/v( on the E (%) of Ti(IV). Conditions: 40 μg L-1 Ti(IV); pH 3; 0.1 mol L-1 Na2SO4; 1.0×10−4 mol L−1 CTAB; 1.0×10−4 mol L−1 ARS; centrifuge time 10 min.
29
ACCEPTED MANUSCRIPT Table 1. Operation parameters for determination of Ti (IV) by ICP-OES.
1350
PT
RF generator power(W) Plasma gas flow rate (L min-1)
15
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Auxiliary gas flow rate (L min-1)
0.2
SC
Nebulizer gas flow rate (L min-1)
Delay time (s) Integration time (s)
MA
Sample uptake rate (mL min-1)
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Pump rate (mL min-1)
0.45 2.5 2.5 7 3 1.5
The number of measurements
3
Wavelength (nm)
Ti 334.940
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TE
D
Sample loop volume (mL)
30
ACCEPTED MANUSCRIPT
Clay 1 (%)
Clay 2 (%)
TiO2
1.014
0.31
1.15
44.388
Fe2O3 tot
14.503
53.54
7.15
51.097
MgO
6.493
1.99
1.61
0.590
Na2O
1.835
0.28
1.32
0.043
Al2O3
14.222
6.34
13.45
0.376
SiO2
49.629
16.7
61.7
1.128
P2O5
0.244
0.45
0.2
0.046
SO3
0.157
-
-
0.016
K2O
1.962
0.21
2
0.020
CaO
6.323
0.91
0.51
0.346
Cr2O3
0.064
0.007
0.013
0.269
0.264
0.65
0.06
1.484
0.082
-
-
0.053
MnO
SC
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D
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NiO
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Component
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Wadi deposits (%)
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Table 2. Composition of real geological samples (%) with XRF analysis.
Black sand (%)
CuO
0.022
-
-
-
ZnO
0.03
-
-
0.041
SrO
0.043
-
-
0.002
ZrO2
0.045
-
-
0.064
Y2O3
.012
-
-
-
LOI
3
18.5
10.6
-
31
ACCEPTED MANUSCRIPT Table 3. Tolerance ratios of diverse ions on pre-concentration and determination of 50 μg L-1of Ti(IV) under optimum conditions. Tolerance ratio
PT
Foreign ions
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Na+, K+, Li+, NH4+, Mg2+, Ca2+,Sr2+, Ba2+, Cl-, I-, NO3-
5000
SC
, SO42 -, thiocyanate, thiourea, thiosulphate, acetate
NU
Ascorbic acid
Mn2+, Cd2 +, Hg2+, Fe2+, Ni2+, Co2+, Zn2+, Pb2+, Cr3+, b
MA
Fe3+ a, Cu2+
D
La3+,Sm3+,Nd3+,Y3+,Gd3+, UO22+ c, Al3+
c
Citrate, oxalate a
Using ascorbic acid.
b
Using thiourea.
c
Using NaH2PO4.
500
200
AC CE P
Zr4+ c, Hf4+
2000
450
TE
PO43-, F-
c
2800
50
32
ACCEPTED MANUSCRIPT Table 4. Analytical figures of merit. Parameter
Analytical feature
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ICP-OES (Spectrophotometry)
Linear range (μg L-1)
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0.3-80 (7-200)
Correlation coefficient (R2)
SC
0.9983 (.9962)
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LOD (μg L-1) LOQ (μg L-1)
MA
Pre-concentration factor
D
Enrichment factor
0.33 (7.67) 100 (100) 97 (80) 2.63(1.96)
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TE
R.S.D %
0.1 (2.3)
33
ACCEPTED MANUSCRIPT Table 5. Comparison of the proposed CPE procedure with other published
morin
technique
(μg L-1)
FAAS
2.9
as
complexing agent and Triton X-114 as surfactant. Solid phase extraction on 2-
ICP-MS
MCI
0.11
GEL
spectrophotometry
AC CE P
nanometer size ZrO2.
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Solid phase extraction with
Linearity
Samples
References
20 (PF)
0.02-2.0 μg mL-1
Water and plant
[16]
samples
—
Water
[8]
samples
D
CHP20P resin.
61 (PF)
MA
nitroso-1-naphthol impregnated
EF
SC
using
LOD
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CPE
Detection
RI
Method
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methods in literature for separation and determination of Ti(IV).
0.1
100
—
Water
[9]
samples
Solid phase extraction with activated carbon. .
ICP-OES
0.01
80
—
Seawater samples
[10]
spectrophotometry
0.4
—
0-1 μg mL-1
Silicate rocks
[14]
ICP-OES
0.1
97,
0.3-80 μg L-1
Water, geological
Present
samples and
work
Micelle mediated extraction into benzene or toluene. CPE
using
ARS
as
complexing agent and mixed surfactant (CTAB and Triton
100(PF)
X-114) in presence of Na2SO4
synthetic mixtures
at room temperature.
FAAS: flame atomic absorption spectrometry, ICP-MS: inductively coupled plasma mass spectrometry. 34
ACCEPTED MANUSCRIPT Table 6. Recovery of 20 µg L-1 Ti(IV) in synthesized mixtures in presence of 100 µg L-1 of interfering ion and using the masking mixture by the
100.90
RI
NU
Fe(III), Al(III), Sr(II), Cd(II)
D
MA
Fe(III), Zr(IV), Cr(III), Co(II)
TE
Fe(III),Gd(III), UO2(II), La(III) *
20.18 .94
SC
Fe(III), Cu(II), Zn(II), Mg(II)
Fe(III), Mn(II), Ni(II), Hg(II)
E (%)
Ti(IV) found (µg L-1) *
Synthetic mixtures
Fe(III), Sm(III), Nd(III), Y(III)
PT
recommended procedure.
AC CE P
The results are the mean of five measurements
35
20.45
102.25
19.76
98.80
20.68
103.40
19.41
97.05
20.54
102.70
standard deviation.
ACCEPTED MANUSCRIPT Table 7. Analytical results of TiO2 analysis in geological samples.
ICP-OES*
critical=2.57
critical=7.146
Spectrophotometry*
RI
XRF
F5,5-testiii
PT
TiO2 (wt %)i
Samples
t-testii
1.014
1.034
025 (2.42)
1.022
022 (2.12)
1.79
1.29
Clay 1
0.310
0.317
011(3.47)
0.307
01 (3.26)
1.42
1.21
Clay 2
1.150
1.168 0.032(2.74 )
1.144 0.04(3.50)
1.26
1.56
Black sand
44.388
44.906
1.10
1.15
*
NU
(2.34)
SC
Wadi deposits
45.066
i
t-test between XRF and ICP-OES measurements. F- test between ICP-OES and spectrophotometry measurements.
AC CE P
iii
TE
D
ii
TiO2 was determined from Ti(IV).
standard deviation (R.S.D %).
MA
The results are the mean of five measurements
(2.49)
36
ACCEPTED MANUSCRIPT Table 8. Analytical results of Ti(IV) determination in water samples. Ti(IV) µg L-1 Added
Found*
E (%)
Tap water
0
N.D
-
RI
PT
sample
5
SC
5.08
10
NU
9.85
102.2
11.10
100.3
0
3.55
-
5
8.52
99.4
10
13.69
101.4
MA D TE
98.5
6.18
10
AC CE P
15
-
0 5
Mineral water
101.6
1.07
Sea water
River water
09
0
N.D
-
5
4.88
97.6
10
9.96
99.6
N.D : not detectable. *
The results are the mean of five measurements
37
standard deviation.
ACCEPTED MANUSCRIPT Table 9. Analytical results of Ti(IV) determination in simulated reference
PT
materials.
Ti (IV) found (wt %)*
RI
Samples
Simulated NKK CRM No. 920
0.153
006
Simulated NKK CRM No. 1021
0.041
MA
(Al, Si, Cu, Zn, alloy) b
NU
(Al alloy) a
*
Spectrophotometry
SC
ICP-OES
The results are the mean of five measurements
a
0.149
008
0.039
standard deviation
D
Si, 0.78; Fe, 0.729; Mg, 0.46; Cr, 0.27; Bi, 0.06; Ga, 0.05; Ca, 0.03; Co,
Si, 5.56; Fe, 0.99; Mg, 0.29; Cr, 0.03; Sn, 0.10; Pb, 0.18; Sb, 0.01; Zr, 0.01;
AC CE P
b
TE
0.10; Ni, 0.29; V, 0.15; Cu, 0.71; Mn, 0.20, Zn, 0.80; Ti, 0.15
Bi, 0.01; V, 0.007; Ca, 0.004; Mn, 0.11; Ni, 0.14; Cu, 2.72, Zn, 1.76; Ti, 0.04
38
ACCEPTED MANUSCRIPT Figure captions Scheme 1. Structure of Alizarin red S.
PT
Figure 1. Effect of the pH on the E(%) of Ti(IV). Conditions: 40 μg L-1 Ti
RI
(IV); 1.0×10−4 mol L−1 ARS; 0.1 mol L-1 Na2SO4; 0.1% w/v Triton X-114;
SC
1.0×10−4 mol L−1 CTAB; centrifuge time 10 min.
NU
Figure 2. Effect of the ARS concentration on the E (%) of Ti(IV). Conditions: 40 μg L-1 Ti (IV); pH 3; 0.1 mol L-1 Na2SO4; 0.1% w/v Triton X-
MA
114; 1.0×10−4 mol L−1 CTAB; centrifuge time 10 min.
D
Figure 3. Effect of the CTAB concentration on the E (%) of Ti(IV).
TE
Conditions: 40 μg/L Ti(IV); pH 3; 0.1 mol L-1 Na2SO4; 0.1% w/v Triton X-
AC CE P
114; 1.0×10−4 mol L−1 ARS; centrifuge time 10 min. Figure 4. Effect of the Triton X-114 concentration )w/v( on the E (%) of Ti(IV). Conditions: 40 μg L-1 Ti(IV); pH 3; 0.1 mol L-1 Na2SO4; 1.0×10−4 mol L−1 CTAB; 1.0×10−4 mol L−1 ARS; centrifuge time 10 min.
39
ACCEPTED MANUSCRIPT Highlights:
AC CE P
TE
D
MA
NU
SC
RI
PT
A CPE procedure for selective Ti(IV) enrichment from different matrices is proposed. The analytical parameters indicate the high validation of the procedure. The procedure is applied for determination of Ti(IV) in geological and water samples.
40