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A new portable micropipette tip-syringe based solid phase microextraction for the determination of vanadium species in water and food samples
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JIEC 3570 1–5 Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
A new portable micropipette tip-syringe based solid phase microextraction for the determination of vanadium species in water and food samples
1 2 3
4 Q1
Naeemullaha,b , Mustafa Tuzena,* , Tasneem Gul Kazib
5 6
a b
Gaziosmanpaşa University, Faculty of Science and Arts, Chemistry Department, 60250 Tokat, Turkey National Centre of Excellence in Analytical Chemistry University of Sindh, Jamshoro 76080, Pakistan
A R T I C L E I N F O
Article history: Received 26 December 2016 Received in revised form 24 July 2017 Accepted 13 August 2017 Available online xxx Keywords: Multiwalled carbon nanotubes Portable micropipette tip Syringe Vanadium speciation Solid phase microextraction
A B S T R A C T
Simple, rapid and miniaturized portable micropipette tip-syringe solid phase microextraction method was developed for speciation of vanadium in water and food samples. Tetra ethylene pentamine functionalized multiwalled carbon nanotubes were synthesized and packed in micropipette tip-syringe system. The surface morphology of adsorbent was characterized, and the effective factors that influence the efficiency of developed method such as pH, amount of adsorbent, concentration of acid solution for desorption cycles were studied. The V(V) could be adsorbed on the modified adsorbent surface with tetra ethylene pentamine, while V(IV) could not be retained. The assay of V(IV) was based on subtracting values of V(V), from total vanadium. The extracted total vanadium and V(V) were injected directly into the electrothermal atomic absorption spectrometry for analysis. Enhancement factor and detection limit were found 50 and 0.008 mg L 1, respectively. Accuracy of the method was checked by analysis of certified reference materials. The developed method was applied to water and food samples. © 2017 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
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1 Introduction
8
Vanadium is considered to be one of the most important and strategic metals having widespread application in many fields [1]. Generally, vanadium exists in two oxidation states. tetravalent (IV) and pentavalent (V) in aquatic environment. It was reported that V (V) is highly toxic species as compared to V(IV), and have a strong inhibiting activity of the essential metal with enzymes [2,3]. Therefore, a great effort has needed to quantify the low concentration of vanadium in different environmental and biological samples. The different species of vanadium determination have hold a great deal of space in modern literature due to their different chemical, toxic behavior and effects on the environment, animal and human health [3–5]. Vanadium exists in different charge species such as V(V), which exists as VO2+ and VO43 at different pH values. The V(IV), mainly exists as VO2+, in the reducing environmental solution and stable in acidic conditions, whereas at higher pH oxidized to V(V) [4–8]. Several instrumental analytical techniques have been launched to
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Q2
* Corresponding author. Fax: +90 3562521585. E-mail addresses: [email protected], [email protected] (M. Tuzen).
quantify and determined vanadium species at trace levels in different environmental samples [7,9–12]. Electrothermal atomic absorption spectrometry (ETAAS) is one of the most applicable technique for the elemental determination in trace levels with low detection limit, reduced the usage and exposure of toxic chemicals to the environment [12–17]. Vanadium is found to be in trace levels in real water samples [18,19]. Separation and preconcentration process is one of the most growing trend to obtain reliable, precise and accurate trace metals results, thus separation-enrichment steps is an important step prior to the quantification of traces of analytes [20,21]. There are number of separation approaches, which have been used for preconcentration and determination of the trace levels of vanadium in different environmental and biological samples [22,23]. Solid phase microextraction (SPME) is one of the most applicable sample preparation trend due to their unique properties and environmental perspectives [24]. The SPME method is preferred approaches due to their simple operation, reduced consumption of the toxic organic chemicals, high extraction capability, excellent sensitivity and high preconcentration factor [25]. Carbon nanotubes have grabbed a great space in the materials and separation science, due to excellent adsorption of metal ions at trace levels, because of their structural characteristics with high
http://dx.doi.org/10.1016/j.jiec.2017.08.021 1226-086X/© 2017 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Please cite this article in press as: Naeemullah, et al., A new portable micropipette tip-syringe based solid phase microextraction for the determination of vanadium species in water and food samples, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.08.021
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surface area. Their high surface area and excellent extraction capability of carbon nanotubes, make it a popular solids event for the extraction approaches [26,27]. Multiwalled carbon nanotubes (MWNTs) is one of the most popular and applicable attractive materials due to unique physical and chemical structure [28]. According to our literature survey, miniaturized portable micropipette tip-syringe solid phase microextraction (MTS-SPME) method has not been used for the speciation of inorganic vanadium in real samples. In the current study a novel approach of modified/functionalized MWCNTs with tetra ethylene pentamine (TEPA), retained by a micropipette tip couple with syringe system was designed for the determination of total and species of vanadium in real water and food samples. The factors that influence the enrichment capability of the portable TEPA-MWCNTs retained micropipette tip-syringe system was studied and optimized. The optimized (MTS-SPME) procedure was applied to determine the trace levels of vanadium species in the real samples.
with 50–200 mL of 2.0 mol L 1 of HNO3 from the syringe system into a small vial (2 mL in capacity) using 2–10 desorption cycles. A 20 mL aliquot of the eluate sucked up into the syringe and injected manually into the graphite furnace for vanadium determination in the standards/real samples. Total inorganic vanadium was determined after the oxidation of V(IV) to V(V) with 8 mmol L 1 of KMnO4. The amount of V(IV) was calculated by subtracting V(V) from the total vanadium.
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3 Result and discussion
113
3.1 Optimization of ETAAS parameters
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2 Experimental
The optimization of the pyrolysis and atomization temperatures has a key role on the signal intensity and efficiency of vanadium determination by desired method. The effect of different pyrolysis and atomization temperature under optimized conditions were investigated. The efficient and reliable analytical response were obtained by using pyrolysis and atomization temperature at 1400 and 2000 C, respectively, as shown in Fig. 1.
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2.1 Chemical, reagents and glassware
3.2 Optimization of MTS-SPME procedures
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68
Several factors have a key role on the extraction capability and performance of the proposed methods were studied and optimized.
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78
2.2 Instrumentation
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A Perkin Elmer Analyst model 700 and atomizer HGA-800 (Norwalk, CT, USA) atomic absorption spectrometer was used for the vanadium determination, using V hollow cathode lamp at 318.5 nm with a slit width of 0.7 nm. The previously operating instrumental conditions were used for the vanadium determination [29]. A Perkin Elmer AS-800 autosampler was used to automatically injected 20 mL sample containing 5 mL of a matrix modifier Mg(NO3)2 and Pd(NO3)2 into the graphite furnace tube.
3.2.1 Effect of pH Functionalized surface of the MWCNTs has an important task on the extraction efficiency and vanadium speciation of the proposed method. Vanadium has a variety of oxidation state in the sample solution, but mostly V(IV) and V(V) are exist in environmental samples. Vanadium (V) exists in both cationic VO2+ and anionic forms VO43 , respectively. Vanadium(IV) is found in cationic form VO2+. It can be seen in Fig. 2 that V(V) could be quantitatively adsorbed on the surface of MWCNT at pH >3, while on other side V (IV) could not retained at that pH. In the proposed method, pH 4 was chosen for the selective separation of V(V) from V(IV), as shown in Fig. 2. The different adsorption behaviors of V(V) and V (IV) on the surface of modified MWCNTs could be elaborated on the basis of functional group and chemical behavior of the twooxidation state of vanadium. In the slightly acidic condition the amine functional group has a positive charge and function as a weak-base anion-exchange resin, while V(V) present in the anionic form such as (H2VO4 ), therefore V(V) quantitatively retained on the surface of the MWCNTs by electrostatic interaction. Whereas V
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The stock standard solution of 1000 mg L 1 V(V) and V(IV) were prepared by dissolving appropriate amount of NH4VO3 and VOSO4 5H2O, respectively (Merck, Darmstadt, Germany). Tetra ethylene pentaamine was obtained from Merck. Phosphate, acetate, borate and ammonia buffer solutions (0.1 mol L 1) were used throughout the experiment to obtained the desired pH of the solutions. The pipette tip and syringe were obtained from Huaxin chemical reagent (Baoding, China) was used. Multi-walled carbon nanotubes (Aldrich Milwaukee, WI, USA) were used according to the information reported by the manufacturer [28].
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69 70 71 72 73 74 75 76
80 81 82 83 84 85 86 87
2.3 Preparation and characterization of TEPA-MWCNTs
88 90
The TEPA immobilized MWCNTs were prepared in a beaker with magnet stirring. The detail of preparation and characterization was presented in our previous work [28].
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2.4 Procedure of MTS-SPME method
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The desired portable MTS-SPME operating in-syringe system is quite easy, the micropipette tip was preconditioned with acidic ethanol to the make surface free of matrix which might affect on the extraction efficiency and results. Then 1–10 mg of MWCNTsTEPA was introduced into the micropipette tips and coupled with the syringe. Replicate 5 mL of each standard (0.5–10.0 mg L 1) of V (V) and real sample were taken in beakers separately and the pH of solutions were maintained in the range of 2–8 using related buffer solutions. Then the solution was sucked up into the syringe system and push back into the beaker. These two steps are known as one MTS-SPME operating in-syringe system cycle. In the proposed method, 2–12 cycles were applied for optimum adsorption, during two min. Finally, analyte retained on MWCNTs-TEPA were eluted
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Fig. 1. Pyrolysis (&) and atomization (*) temperature curves for 2.0 mg L 1 V(V) in the presence of 4.5 mg of TEPA-MWCNTs, pH 3, 3 mL sample volume, 8 adsorption cycles of extraction (2.0 min), 5 desorption cycles with 100 mL of 2 mol L 1 HNO3.
Please cite this article in press as: Naeemullah, et al., A new portable micropipette tip-syringe based solid phase microextraction for the determination of vanadium species in water and food samples, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.08.021
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3
Table 1 Tolerance limit of the common coexisting ions on proposed (MTS-SPME) method. Q5
Fig. 2. Effect of pH on the recovery (%) of V(V) and V(IV) 2.0 mg L 1, 4.5 mg of TEPAMWCNTs, 3 mL sample volume, 8 adsorption cycles of extraction (2.0 min), 5 desorption cycles with 100 mL of 2 mol L 1 HNO3. 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170
(IV) is present mainly in the cationic form their interaction is lower than V(V).
VO2+
[30,31]. Therefore,
3.2.2 Amount of TEPA-MWCNTs The amount of MWCNTs filled into micropipette tip syringe system has key role on the reliability of the proposed method. In the proposed method, experimental serried were carried out filled the amount of TEPA-MWCNTs in the range of 1.0–10.0 mg. From the following experiment, it was concluded that the behavior of the TEPA-MWCNTs was almost quantitative >95% at above 4.0 mg, then 4.5 mg was selected for further experiments (Fig. 3). The MWCNTs have multidimensional structures and excellent adsorption capacity enhanced the portability and capability of the desired method. 3.2.3 The role of adsorption/desorption cycles The adsorption cycles play an important role in the extraction efficiency of the proposed method. The effects of adsorption/ desorption cycles on the extraction/preconcentration of the vanadium were studied in the range of 2–12. It has been observed that maximum signal/extraction efficiency of vanadium for adsorption was observed after 8 cycles in 2.0 min. Thus, we concluded from the experimental results that 8 cycles are sufficient for removal of the vanadium from the real sample by portable MTS-SPME in 2 min. The effect of desorption cycles (2–10) on optimum recovery of analyte was studied. It was observed that optimum signal of analyte was obtained after 5 desorption cycles in 1 min.
Ions
Tolerance limit (mg/L) (ions/(V(IV), V(V)
Recovery (%)
Na+ K+ Ca2+ Mg2+ SO42 Cl HCO3 CO32 Al3+ Fe3+ Pb2+ Zn2+ Cr3+ Cd2+
5000 3000 2000 2000 2000 10000 1500 1500 30 25 25 30 30 30
97 2 97 3 98 2 97 3 98 1 98 2 97 3 98 1 97 2 95 3 96 2 98 3 97 2 97 3
3.2.4 Sample volume In the proposed method, we also studied the role of the sample volume on the proposed (MTS-SPME) method to achieve precise and accurate results. The experiment was designed to investigate the role of breakthrough volume in the range of 1–10 mL. The results indicate that 3 mL of the sample volume have shown excellence and reliable extraction efficiency while further increased in the sample volume have no effect on the extraction capability of the desired method. As the small sample volume is the prime requirement in the miniaturizing sample operating process. Therefore, present developed method reduced the exposure of used chemicals to the environment which is the main theme of the green chemistry.
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3.2.5 The role of the volume and concentration of elution solution The elution solvent is considered to be one of the most significant variable, which play a key role for desorption of the analyte ions from TEPA- MWCNTs and their chemical effect on the surface of the adsorbent. The effect of volume and concentration of desorption solvent (HNO3) in the ranged of 50–200 mL and 0.5–2.5 mol L 1, respectively were studied. It was observed that the desorption efficiency was maximum at concentration and volume corresponds to 2.0 mol L 1 and 100 mL of HNO3, respectively. The resulted data indicated that the quantitative desorption result could not achieve at concentration less than 2.0 mol L 1. That might be due to strong metal interaction on the surface of the MWCNTs, that could not be desorbed. The low volume of the desorption solvent (HNO3) was used to enhance sensitivity, higher preconcentration factor and feasibility of the proposed method.
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3.3 Interference studies
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The selectivity and applicability of the proposed MTS-SPME method was investigated by the effects of interfering ions at optimum variables conditions. To point out the effects of interfering ions by adding different concentration of the coexisting ions to 5 mL solution of 2.0 mg L 1 of vanadium. It has been observed that at selected concentration of coexisting ions, the
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Table 2 Determination of vanadium in certified reference materials by (MTS-SPME) method. Certified reference material
Certified values
Measured values
Recovery (%)
0.36
0.35
97 2
NIST SRM 1515 Apple Leaves (mg g 0.26 1 )
0.25
96 2
SLRS-4-Riverine water (mg L Fig. 3. Effect of the amount of SMWCNTs on the recovery (%) of (DSLME): V(V) and V (IV) 2.0 mg L 1, pH 4.0, 4.5 mg of TEPA-MWCNTs, 3 mL sample volume, 8 adsorption cycles of extraction (2.0 min), 5 desorption cycles with 100 mL of 2 mol L 1 HNO3.
1
)
Please cite this article in press as: Naeemullah, et al., A new portable micropipette tip-syringe based solid phase microextraction for the determination of vanadium species in water and food samples, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.08.021
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Table 3 Vanadium speciation in real water samples by using spiking addition of present method (N: 3). Added (mg L
Samples
Found (mg L
1
) V(V)
V (IV)
Total V
V(V)
V (IV)
Total V
0 0.50 1.00
0.46 0.04a 0.95 0.06 1.44 0.10
0.13 0.01 0.62 0.04 1.13 0.08
0.58 0.02 1.09 0.10 1.56 0.12
– 98 2 99 1
– 98 2 100 2
– 102 2 98 2
Sea water
0 0.50 1.00
0.88 0.06 1.37 0.07 1.86 0.1
0.42 0.03 0.90 0.06 1.40 0.09
1.32 0.11 1.81 0.14 2.30 0.15
– 99 2 98 3
– 96 2 98 3
– 99 2 98 3
Drinking water
0 0.50 1.00
0.42 0.02 0.91 0.07 1.43 0.10
0.16 0.01 0.66 0.05 1.15 0.11
0.58 0.02 1.06 0.09 1.58 0.13
– 99 2 101 1
– 100 2 99 2
– 96 2 100 2
Mean + SD (n = 3).
Food samples
Measured values (mg g
Spinach Cultivated mushroom White wine Apple Tomato Banana
0.24 0.02a 0.18 0.01 15.5 0.09 mg L 0.60 0.04 0.14 0.01 0.16 0.01
a
1
)
1
Mean SD (n = 3).
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tolerance limit of the coexisting ions, was less than 5%. Thus, the proposed method could be successfully applied to the real samples in the presence of these coexisting ions (Table 1).
209
3.4 Analytical capability
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The analytical capacity and efficiency of the proposed MTSSPME method was investigated under the optimized experimental conditions. In the present study, a good linear calibration graph was achieved at the concentration range of 0.5–10 mg L 1 with correlation coefficient (r2) of 0.999. The limit of detection (LOD), after the preconcentration was 0.008 mg L 1. The repeatability and precision of the proposed method was checked by analyzing five replicates analysis of 2.0 mg L 1 of vanadium by developed method, and the relative standard deviation (% RSD) was found to be 3.5%. The enhancement factor was calculated as the ratio of the slopes of calibration graphs with and without preconcentration of V(V) was found to be 50. The accuracy of the MTS-SPME method was checked by analysis of certified reference materials (SLRS4 Riverine water and NIST SRM 1515 Apple leaves). The % recovery is greater than 95%, which conformed that the developed method is highly valid and applicable (Table 2).
211 212 213 214 215 216 217 218 219 220 221 222 223 224 225
Recovery (%)
V(V)/V(IV)
Table 4 Determination of total vanadium in real food samples by MTS-SPME method.
207
)
Tap water
a
206
1
3.5 Application to real samples
226
The water samples of different ecosystem (tap water and drinking water samples) were collected from Tokat city, Turkey. Sea water samples was collected from Black sea, Turkey. The proposed method under optimized condition was successfully applied to quantify the trace levels of vanadium (V) and V(IV) in real water samples (Table 3). The MTS-SPME method was also applied to determined total vanadium in acid digested solid samples. NIST SRM 1515 Apple leaves standard reference material (250 mg), banana, tomato, apple, cultivated mushroom, spinach (1.0 g) and white wine (1 mL) were digested with 6 mL of HNO3 (65%) and 2 mL of H2O2 (30%) in the closed microwave digestion system. Digestion conditions of microwave system for the samples were applied as reported in previous work [29]. The proposed method was applied and the results are given in Table 4. To determine the total vanadium, in water samples, 10.0 mmol L 1 of KMnO4 was used to oxidized V(IV) to V(V), then applied proposed method.
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4 Conclusion
244
The developed portable (MTS-SPME) method is a model sample preparation approach due to their simplicity, miniaturization and consumption of low sample volume, which is one of the prime perspective of the green chemistry and excellent replaceable approach of the conventional SPE. The vanadium speciation was successfully carried out by MTS-SPME method. The advantage of this method over the other is their simplicity and extraction capability and portability. The durability and stability of MWCNTsTEPA was observed over 120 adsorption–desorption cycles, to analysed more than 10 samples/standards, once prepared portable syringe. The efficiency of developed procedure is compared with literature reported methodologies, indicates in Table 5 [30,32–36]. Sample volume, extraction time, LOD and RSD values of present
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Table 5 Comparative analytical capability of the present method with previously reported methods for vanadium. Methods SPE TPLLME SPE SPE SPE SPE MTS-SPME
LOD (mg L 0.015 0.034 0.009 – 0.015 0.020 0.008
1
Linear ranged (mg L
1
)
RSD (%)
Sample volume (mL)
Extraction time (min)
EF
References
1.23 4.32 1.5 5.4 1.8 6 3.5
0.40 20 5 75 10 40 3
– – 1
– 100 35 150 10 – 50
[32] [33] [34] [30] [35] [36] This work
) – 0.30–4.0 0.08–10 – – – 0.5–10
10 – 2
LOD: limit of detection, EF: enhancement factor, SPE: solid phase extraction, TPLLME: tri phase liquid–liquid microextraction, RSD: relative standard deviation, MTS-SPME: micropipette tip-syringe solid phase microextraction.
Please cite this article in press as: Naeemullah, et al., A new portable micropipette tip-syringe based solid phase microextraction for the determination of vanadium species in water and food samples, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.08.021
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MTS-SPME method are better than other reported methods. We hope this method will be used a screening tools for the quantitative determination of different metals in different environmental samples.
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Acknowledgements
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Naeemullah is grateful to the Scientific and Technological Research Council of Turkey (TUBITAK) for awarding him “2216 Research Fellowship Program for Foreign Citizens” and providing financial support. The authors also would like to thank to Gaziosmanpasa University for excellent facilities in research laboratory to carry out research work.
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Please cite this article in press as: Naeemullah, et al., A new portable micropipette tip-syringe based solid phase microextraction for the determination of vanadium species in water and food samples, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.08.021
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JIEC 3570 1–5 Journal of Industrial and Engineering Chemistry xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
A new portable micropipette tip-syringe based solid phase microextraction for the determination of vanadium species in water and food samples
1 2 3
4 Q1
Naeemullaha,b , Mustafa Tuzena,* , Tasneem Gul Kazib
5 6
a b
Gaziosmanpaşa University, Faculty of Science and Arts, Chemistry Department, 60250 Tokat, Turkey National Centre of Excellence in Analytical Chemistry University of Sindh, Jamshoro 76080, Pakistan
A R T I C L E I N F O
Article history: Received 26 December 2016 Received in revised form 24 July 2017 Accepted 13 August 2017 Available online xxx Keywords: Multiwalled carbon nanotubes Portable micropipette tip Syringe Vanadium speciation Solid phase microextraction
A B S T R A C T
Simple, rapid and miniaturized portable micropipette tip-syringe solid phase microextraction method was developed for speciation of vanadium in water and food samples. Tetra ethylene pentamine functionalized multiwalled carbon nanotubes were synthesized and packed in micropipette tip-syringe system. The surface morphology of adsorbent was characterized, and the effective factors that influence the efficiency of developed method such as pH, amount of adsorbent, concentration of acid solution for desorption cycles were studied. The V(V) could be adsorbed on the modified adsorbent surface with tetra ethylene pentamine, while V(IV) could not be retained. The assay of V(IV) was based on subtracting values of V(V), from total vanadium. The extracted total vanadium and V(V) were injected directly into the electrothermal atomic absorption spectrometry for analysis. Enhancement factor and detection limit were found 50 and 0.008 mg L 1, respectively. Accuracy of the method was checked by analysis of certified reference materials. The developed method was applied to water and food samples. © 2017 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
7
1 Introduction
8
Vanadium is considered to be one of the most important and strategic metals having widespread application in many fields [1]. Generally, vanadium exists in two oxidation states. tetravalent (IV) and pentavalent (V) in aquatic environment. It was reported that V (V) is highly toxic species as compared to V(IV), and have a strong inhibiting activity of the essential metal with enzymes [2,3]. Therefore, a great effort has needed to quantify the low concentration of vanadium in different environmental and biological samples. The different species of vanadium determination have hold a great deal of space in modern literature due to their different chemical, toxic behavior and effects on the environment, animal and human health [3–5]. Vanadium exists in different charge species such as V(V), which exists as VO2+ and VO43 at different pH values. The V(IV), mainly exists as VO2+, in the reducing environmental solution and stable in acidic conditions, whereas at higher pH oxidized to V(V) [4–8]. Several instrumental analytical techniques have been launched to
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* Corresponding author. Fax: +90 3562521585. E-mail addresses: [email protected], [email protected] (M. Tuzen).
quantify and determined vanadium species at trace levels in different environmental samples [7,9–12]. Electrothermal atomic absorption spectrometry (ETAAS) is one of the most applicable technique for the elemental determination in trace levels with low detection limit, reduced the usage and exposure of toxic chemicals to the environment [12–17]. Vanadium is found to be in trace levels in real water samples [18,19]. Separation and preconcentration process is one of the most growing trend to obtain reliable, precise and accurate trace metals results, thus separation-enrichment steps is an important step prior to the quantification of traces of analytes [20,21]. There are number of separation approaches, which have been used for preconcentration and determination of the trace levels of vanadium in different environmental and biological samples [22,23]. Solid phase microextraction (SPME) is one of the most applicable sample preparation trend due to their unique properties and environmental perspectives [24]. The SPME method is preferred approaches due to their simple operation, reduced consumption of the toxic organic chemicals, high extraction capability, excellent sensitivity and high preconcentration factor [25]. Carbon nanotubes have grabbed a great space in the materials and separation science, due to excellent adsorption of metal ions at trace levels, because of their structural characteristics with high
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Please cite this article in press as: Naeemullah, et al., A new portable micropipette tip-syringe based solid phase microextraction for the determination of vanadium species in water and food samples, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.08.021
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surface area. Their high surface area and excellent extraction capability of carbon nanotubes, make it a popular solids event for the extraction approaches [26,27]. Multiwalled carbon nanotubes (MWNTs) is one of the most popular and applicable attractive materials due to unique physical and chemical structure [28]. According to our literature survey, miniaturized portable micropipette tip-syringe solid phase microextraction (MTS-SPME) method has not been used for the speciation of inorganic vanadium in real samples. In the current study a novel approach of modified/functionalized MWCNTs with tetra ethylene pentamine (TEPA), retained by a micropipette tip couple with syringe system was designed for the determination of total and species of vanadium in real water and food samples. The factors that influence the enrichment capability of the portable TEPA-MWCNTs retained micropipette tip-syringe system was studied and optimized. The optimized (MTS-SPME) procedure was applied to determine the trace levels of vanadium species in the real samples.
with 50–200 mL of 2.0 mol L 1 of HNO3 from the syringe system into a small vial (2 mL in capacity) using 2–10 desorption cycles. A 20 mL aliquot of the eluate sucked up into the syringe and injected manually into the graphite furnace for vanadium determination in the standards/real samples. Total inorganic vanadium was determined after the oxidation of V(IV) to V(V) with 8 mmol L 1 of KMnO4. The amount of V(IV) was calculated by subtracting V(V) from the total vanadium.
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3 Result and discussion
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3.1 Optimization of ETAAS parameters
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2 Experimental
The optimization of the pyrolysis and atomization temperatures has a key role on the signal intensity and efficiency of vanadium determination by desired method. The effect of different pyrolysis and atomization temperature under optimized conditions were investigated. The efficient and reliable analytical response were obtained by using pyrolysis and atomization temperature at 1400 and 2000 C, respectively, as shown in Fig. 1.
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2.1 Chemical, reagents and glassware
3.2 Optimization of MTS-SPME procedures
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Several factors have a key role on the extraction capability and performance of the proposed methods were studied and optimized.
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2.2 Instrumentation
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A Perkin Elmer Analyst model 700 and atomizer HGA-800 (Norwalk, CT, USA) atomic absorption spectrometer was used for the vanadium determination, using V hollow cathode lamp at 318.5 nm with a slit width of 0.7 nm. The previously operating instrumental conditions were used for the vanadium determination [29]. A Perkin Elmer AS-800 autosampler was used to automatically injected 20 mL sample containing 5 mL of a matrix modifier Mg(NO3)2 and Pd(NO3)2 into the graphite furnace tube.
3.2.1 Effect of pH Functionalized surface of the MWCNTs has an important task on the extraction efficiency and vanadium speciation of the proposed method. Vanadium has a variety of oxidation state in the sample solution, but mostly V(IV) and V(V) are exist in environmental samples. Vanadium (V) exists in both cationic VO2+ and anionic forms VO43 , respectively. Vanadium(IV) is found in cationic form VO2+. It can be seen in Fig. 2 that V(V) could be quantitatively adsorbed on the surface of MWCNT at pH >3, while on other side V (IV) could not retained at that pH. In the proposed method, pH 4 was chosen for the selective separation of V(V) from V(IV), as shown in Fig. 2. The different adsorption behaviors of V(V) and V (IV) on the surface of modified MWCNTs could be elaborated on the basis of functional group and chemical behavior of the twooxidation state of vanadium. In the slightly acidic condition the amine functional group has a positive charge and function as a weak-base anion-exchange resin, while V(V) present in the anionic form such as (H2VO4 ), therefore V(V) quantitatively retained on the surface of the MWCNTs by electrostatic interaction. Whereas V
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The stock standard solution of 1000 mg L 1 V(V) and V(IV) were prepared by dissolving appropriate amount of NH4VO3 and VOSO4 5H2O, respectively (Merck, Darmstadt, Germany). Tetra ethylene pentaamine was obtained from Merck. Phosphate, acetate, borate and ammonia buffer solutions (0.1 mol L 1) were used throughout the experiment to obtained the desired pH of the solutions. The pipette tip and syringe were obtained from Huaxin chemical reagent (Baoding, China) was used. Multi-walled carbon nanotubes (Aldrich Milwaukee, WI, USA) were used according to the information reported by the manufacturer [28].
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2.3 Preparation and characterization of TEPA-MWCNTs
88 90
The TEPA immobilized MWCNTs were prepared in a beaker with magnet stirring. The detail of preparation and characterization was presented in our previous work [28].
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2.4 Procedure of MTS-SPME method
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The desired portable MTS-SPME operating in-syringe system is quite easy, the micropipette tip was preconditioned with acidic ethanol to the make surface free of matrix which might affect on the extraction efficiency and results. Then 1–10 mg of MWCNTsTEPA was introduced into the micropipette tips and coupled with the syringe. Replicate 5 mL of each standard (0.5–10.0 mg L 1) of V (V) and real sample were taken in beakers separately and the pH of solutions were maintained in the range of 2–8 using related buffer solutions. Then the solution was sucked up into the syringe system and push back into the beaker. These two steps are known as one MTS-SPME operating in-syringe system cycle. In the proposed method, 2–12 cycles were applied for optimum adsorption, during two min. Finally, analyte retained on MWCNTs-TEPA were eluted
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Fig. 1. Pyrolysis (&) and atomization (*) temperature curves for 2.0 mg L 1 V(V) in the presence of 4.5 mg of TEPA-MWCNTs, pH 3, 3 mL sample volume, 8 adsorption cycles of extraction (2.0 min), 5 desorption cycles with 100 mL of 2 mol L 1 HNO3.
Please cite this article in press as: Naeemullah, et al., A new portable micropipette tip-syringe based solid phase microextraction for the determination of vanadium species in water and food samples, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.08.021
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Table 1 Tolerance limit of the common coexisting ions on proposed (MTS-SPME) method. Q5
Fig. 2. Effect of pH on the recovery (%) of V(V) and V(IV) 2.0 mg L 1, 4.5 mg of TEPAMWCNTs, 3 mL sample volume, 8 adsorption cycles of extraction (2.0 min), 5 desorption cycles with 100 mL of 2 mol L 1 HNO3. 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170
(IV) is present mainly in the cationic form their interaction is lower than V(V).
VO2+
[30,31]. Therefore,
3.2.2 Amount of TEPA-MWCNTs The amount of MWCNTs filled into micropipette tip syringe system has key role on the reliability of the proposed method. In the proposed method, experimental serried were carried out filled the amount of TEPA-MWCNTs in the range of 1.0–10.0 mg. From the following experiment, it was concluded that the behavior of the TEPA-MWCNTs was almost quantitative >95% at above 4.0 mg, then 4.5 mg was selected for further experiments (Fig. 3). The MWCNTs have multidimensional structures and excellent adsorption capacity enhanced the portability and capability of the desired method. 3.2.3 The role of adsorption/desorption cycles The adsorption cycles play an important role in the extraction efficiency of the proposed method. The effects of adsorption/ desorption cycles on the extraction/preconcentration of the vanadium were studied in the range of 2–12. It has been observed that maximum signal/extraction efficiency of vanadium for adsorption was observed after 8 cycles in 2.0 min. Thus, we concluded from the experimental results that 8 cycles are sufficient for removal of the vanadium from the real sample by portable MTS-SPME in 2 min. The effect of desorption cycles (2–10) on optimum recovery of analyte was studied. It was observed that optimum signal of analyte was obtained after 5 desorption cycles in 1 min.
Ions
Tolerance limit (mg/L) (ions/(V(IV), V(V)
Recovery (%)
Na+ K+ Ca2+ Mg2+ SO42 Cl HCO3 CO32 Al3+ Fe3+ Pb2+ Zn2+ Cr3+ Cd2+
5000 3000 2000 2000 2000 10000 1500 1500 30 25 25 30 30 30
97 2 97 3 98 2 97 3 98 1 98 2 97 3 98 1 97 2 95 3 96 2 98 3 97 2 97 3
3.2.4 Sample volume In the proposed method, we also studied the role of the sample volume on the proposed (MTS-SPME) method to achieve precise and accurate results. The experiment was designed to investigate the role of breakthrough volume in the range of 1–10 mL. The results indicate that 3 mL of the sample volume have shown excellence and reliable extraction efficiency while further increased in the sample volume have no effect on the extraction capability of the desired method. As the small sample volume is the prime requirement in the miniaturizing sample operating process. Therefore, present developed method reduced the exposure of used chemicals to the environment which is the main theme of the green chemistry.
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3.2.5 The role of the volume and concentration of elution solution The elution solvent is considered to be one of the most significant variable, which play a key role for desorption of the analyte ions from TEPA- MWCNTs and their chemical effect on the surface of the adsorbent. The effect of volume and concentration of desorption solvent (HNO3) in the ranged of 50–200 mL and 0.5–2.5 mol L 1, respectively were studied. It was observed that the desorption efficiency was maximum at concentration and volume corresponds to 2.0 mol L 1 and 100 mL of HNO3, respectively. The resulted data indicated that the quantitative desorption result could not achieve at concentration less than 2.0 mol L 1. That might be due to strong metal interaction on the surface of the MWCNTs, that could not be desorbed. The low volume of the desorption solvent (HNO3) was used to enhance sensitivity, higher preconcentration factor and feasibility of the proposed method.
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3.3 Interference studies
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The selectivity and applicability of the proposed MTS-SPME method was investigated by the effects of interfering ions at optimum variables conditions. To point out the effects of interfering ions by adding different concentration of the coexisting ions to 5 mL solution of 2.0 mg L 1 of vanadium. It has been observed that at selected concentration of coexisting ions, the
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Table 2 Determination of vanadium in certified reference materials by (MTS-SPME) method. Certified reference material
Certified values
Measured values
Recovery (%)
0.36
0.35
97 2
NIST SRM 1515 Apple Leaves (mg g 0.26 1 )
0.25
96 2
SLRS-4-Riverine water (mg L Fig. 3. Effect of the amount of SMWCNTs on the recovery (%) of (DSLME): V(V) and V (IV) 2.0 mg L 1, pH 4.0, 4.5 mg of TEPA-MWCNTs, 3 mL sample volume, 8 adsorption cycles of extraction (2.0 min), 5 desorption cycles with 100 mL of 2 mol L 1 HNO3.
1
)
Please cite this article in press as: Naeemullah, et al., A new portable micropipette tip-syringe based solid phase microextraction for the determination of vanadium species in water and food samples, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.08.021
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Table 3 Vanadium speciation in real water samples by using spiking addition of present method (N: 3). Added (mg L
Samples
Found (mg L
1
) V(V)
V (IV)
Total V
V(V)
V (IV)
Total V
0 0.50 1.00
0.46 0.04a 0.95 0.06 1.44 0.10
0.13 0.01 0.62 0.04 1.13 0.08
0.58 0.02 1.09 0.10 1.56 0.12
– 98 2 99 1
– 98 2 100 2
– 102 2 98 2
Sea water
0 0.50 1.00
0.88 0.06 1.37 0.07 1.86 0.1
0.42 0.03 0.90 0.06 1.40 0.09
1.32 0.11 1.81 0.14 2.30 0.15
– 99 2 98 3
– 96 2 98 3
– 99 2 98 3
Drinking water
0 0.50 1.00
0.42 0.02 0.91 0.07 1.43 0.10
0.16 0.01 0.66 0.05 1.15 0.11
0.58 0.02 1.06 0.09 1.58 0.13
– 99 2 101 1
– 100 2 99 2
– 96 2 100 2
Mean + SD (n = 3).
Food samples
Measured values (mg g
Spinach Cultivated mushroom White wine Apple Tomato Banana
0.24 0.02a 0.18 0.01 15.5 0.09 mg L 0.60 0.04 0.14 0.01 0.16 0.01
a
1
)
1
Mean SD (n = 3).
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tolerance limit of the coexisting ions, was less than 5%. Thus, the proposed method could be successfully applied to the real samples in the presence of these coexisting ions (Table 1).
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3.4 Analytical capability
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The analytical capacity and efficiency of the proposed MTSSPME method was investigated under the optimized experimental conditions. In the present study, a good linear calibration graph was achieved at the concentration range of 0.5–10 mg L 1 with correlation coefficient (r2) of 0.999. The limit of detection (LOD), after the preconcentration was 0.008 mg L 1. The repeatability and precision of the proposed method was checked by analyzing five replicates analysis of 2.0 mg L 1 of vanadium by developed method, and the relative standard deviation (% RSD) was found to be 3.5%. The enhancement factor was calculated as the ratio of the slopes of calibration graphs with and without preconcentration of V(V) was found to be 50. The accuracy of the MTS-SPME method was checked by analysis of certified reference materials (SLRS4 Riverine water and NIST SRM 1515 Apple leaves). The % recovery is greater than 95%, which conformed that the developed method is highly valid and applicable (Table 2).
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Recovery (%)
V(V)/V(IV)
Table 4 Determination of total vanadium in real food samples by MTS-SPME method.
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)
Tap water
a
206
1
3.5 Application to real samples
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The water samples of different ecosystem (tap water and drinking water samples) were collected from Tokat city, Turkey. Sea water samples was collected from Black sea, Turkey. The proposed method under optimized condition was successfully applied to quantify the trace levels of vanadium (V) and V(IV) in real water samples (Table 3). The MTS-SPME method was also applied to determined total vanadium in acid digested solid samples. NIST SRM 1515 Apple leaves standard reference material (250 mg), banana, tomato, apple, cultivated mushroom, spinach (1.0 g) and white wine (1 mL) were digested with 6 mL of HNO3 (65%) and 2 mL of H2O2 (30%) in the closed microwave digestion system. Digestion conditions of microwave system for the samples were applied as reported in previous work [29]. The proposed method was applied and the results are given in Table 4. To determine the total vanadium, in water samples, 10.0 mmol L 1 of KMnO4 was used to oxidized V(IV) to V(V), then applied proposed method.
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4 Conclusion
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The developed portable (MTS-SPME) method is a model sample preparation approach due to their simplicity, miniaturization and consumption of low sample volume, which is one of the prime perspective of the green chemistry and excellent replaceable approach of the conventional SPE. The vanadium speciation was successfully carried out by MTS-SPME method. The advantage of this method over the other is their simplicity and extraction capability and portability. The durability and stability of MWCNTsTEPA was observed over 120 adsorption–desorption cycles, to analysed more than 10 samples/standards, once prepared portable syringe. The efficiency of developed procedure is compared with literature reported methodologies, indicates in Table 5 [30,32–36]. Sample volume, extraction time, LOD and RSD values of present
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Table 5 Comparative analytical capability of the present method with previously reported methods for vanadium. Methods SPE TPLLME SPE SPE SPE SPE MTS-SPME
LOD (mg L 0.015 0.034 0.009 – 0.015 0.020 0.008
1
Linear ranged (mg L
1
)
RSD (%)
Sample volume (mL)
Extraction time (min)
EF
References
1.23 4.32 1.5 5.4 1.8 6 3.5
0.40 20 5 75 10 40 3
– – 1
– 100 35 150 10 – 50
[32] [33] [34] [30] [35] [36] This work
) – 0.30–4.0 0.08–10 – – – 0.5–10
10 – 2
LOD: limit of detection, EF: enhancement factor, SPE: solid phase extraction, TPLLME: tri phase liquid–liquid microextraction, RSD: relative standard deviation, MTS-SPME: micropipette tip-syringe solid phase microextraction.
Please cite this article in press as: Naeemullah, et al., A new portable micropipette tip-syringe based solid phase microextraction for the determination of vanadium species in water and food samples, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.08.021
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MTS-SPME method are better than other reported methods. We hope this method will be used a screening tools for the quantitative determination of different metals in different environmental samples.
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Acknowledgements
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Naeemullah is grateful to the Scientific and Technological Research Council of Turkey (TUBITAK) for awarding him “2216 Research Fellowship Program for Foreign Citizens” and providing financial support. The authors also would like to thank to Gaziosmanpasa University for excellent facilities in research laboratory to carry out research work.
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