Selective dispersive micro solid-phase extraction using oxidized multiwalled carbon nanotubes modified with 1,10-phenanthroline for preconcentration of lead ions

Accepted Manuscript Selective dispersive micro solid-phase extraction using oxidized multiwalled carbon nanotubes modified with 1,10-phenanthroline for preconcentration of lead ions Barbara Feist PII: DOI: Reference:

S0308-8146(16)30532-5 http://dx.doi.org/10.1016/j.foodchem.2016.04.015 FOCH 19022

To appear in:

Food Chemistry

Received Date: Revised Date: Accepted Date:

18 September 2015 16 March 2016 10 April 2016

Please cite this article as: Feist, B., Selective dispersive micro solid-phase extraction using oxidized multiwalled carbon nanotubes modified with 1,10-phenanthroline for preconcentration of lead ions, Food Chemistry (2016), doi: http://dx.doi.org/10.1016/j.foodchem.2016.04.015

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Selective dispersive micro solid-phase extraction using oxidized multiwalled carbon

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nanotubes modified with 1,10-phenanthroline for preconcentration of lead ions

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Barbara Feist

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Department of Analytical Chemistry, Institute of Chemistry, University of Silesia,

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40-006 Katowice, Szkolna 9, Poland

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Corresponding author. Fax: +48 32 2599978

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E-mail address: [email protected]

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Abstract

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A dispersive micro solid phase extraction (DMSPE) method for the selective preconcentration

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of trace lead ions on oxidized multiwalled carbon nanotubes (ox-MWCNTs) with complexing

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reagent 1,10-phenanthroline is presented. Flame and electrothermal atomic absorption

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spectrometry (F-AAS, ET-AAS) were used for detection. The influence of several parameters

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such as pH, amount of sorbent and 1,10-phenanthroline, stirring time, concentration and

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volume of eluent, sample flow rate and sample volume was examined using batch procedures.

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Moreover, effects of inorganic matrix on recovery of the determined elements were studied.

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The experiment shows that foreign ions did not influence on recovery of the determined

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element. The method characterized by high selectivity toward Pb(II) ions. Lead ions can be

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quantitatively retained at pH 7 from sample volume up to 400 mL and then eluent completely

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with 2 mL of 0.5 mol L-1 HNO3. The detection limits of Pb was 0.26 µg L-1 for F-AAS and

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6.4 ng L-1 for ET-AAS. The recovery of the method for the determined lead was better than

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97 % with relative standard deviation lower than 3.0 %. The preconcentration factor was 200

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for F-AAS and 100 for ET-AAS. The maximum adsorption capacity of the adsorbent was

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found to be about 350 mg g-1. The method was applied for determination of Pb in fish samples

1

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with good results. Accuracy of the method was verified using certified reference material

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DOLT-3 and ERM - BB186.

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Multiwalled

carbon nanotubes; 1,10-phenanthroline;

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Keywords:

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spectrometry; Lead; Preconcentration; Fish

Atomic

absorption

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1. Introduction

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Various instrumental techniques like flame atomic absorption spectrometry (F-AAS)

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(Ruijun et al, 2011; Nabida et al, 2012), electrothermal atomic absorption spectrometry (ET-

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AAS) (Yang et al, 2011; Alvarez Mendez, Barciela Garcia, Garcia Martin, Peña Crecente, &

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Herrero Latorre, 2015), inductively coupled plasma-optical emission spectrometry (ICP-OES)

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(He, Hu, Jiang, Chang, Tu, & Zhang, 2010; Vellaichamy, & Palanivel, 2011), inductively

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coupled plasma-mass spectrometry (ICP-MS) (Kosanovic, Adem, Jokanovic, & Abdulrazzaq,

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2008) are widely and continuously applied for determination of trace amounts of heavy metal

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ions. ETAAS appears to be a good alternative for the determination of trace lead in

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environmental samples due to its low detection limits, high sensitivity and low cost. However,

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the direct determination of trace of these ions in biological materials is limited and difficult

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because of the complex matrix and the usually low concentration levels. Therefore, a

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chemical separation and preconcentration step is often required prior to analysis.

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Dispersive micro-solid phase extraction (DMSPE) is used commonly for

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preconcentration of different metal ions. Activated carbon, carbon nanotubes, graphene oxide,

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silica gel and aluminum oxide are the most frequently applied solid adsorbents. In this work

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oxidized multi-walled carbon nanotubes (ox-MWCNTs) were proposed as a solid phase.

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Carbon nanotubes (CNTs) have been recently applied in a laboratory as effective

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sorbents for the preconcentration of trace elements using SPE. The large sorbing surface area

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as well as the strong interactions with other molecules make multiwalled carbon nanotubes

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(MWCNTs) an excellent solid sorbent for the preconcentration of traces including metals.

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MWCNTs have been particularly widely used in solid phase (micro)extraction (SPE)

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(Zawisza, Skorek, Stankiewicz, & Sitko, 2012; Duran, Tuzen, & Soylak, 2009). Raw CNTs

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are insoluble and hard to disperse in solvents, due to strong van der Waals interaction that

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hamper sorption of metal ions. Proper surface treatment of CNTs enhance dispersibility and

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improve metal sorption and selectivity. Modified CNTs can be prepared trough loading with

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chemical modifier or through chemical functionalization (Sitko, Zawisza, & Malicka, 2012).

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In the first case, CNTs are loaded with chelating agent (inert chelates), that is not chemically

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bonded to the CNTs surface – sorption mechanism (Sitko, Gliwinska, Zawisza, & Feist, 2013;

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Mohammadi, Afzali, & Pourtalebi, 2010; Vellaichamy, & Palanivelu, 2011). In the second

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case, chemical groups, which can form complexes with metal ions, are chemically bonded to

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the CNTs surface (Zang, Hu, Li, He, & Chang, 2009; Hu, Cui, Liu, Yuan, & Gao, 2012;

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Parodi, Savio, Martinez, Gil, & Smichowski, 2011). Application of chelating agents requires

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often the use of organic solvents for the elution step or ultrasound assistance.

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1,10-phenanthroline is one of the effective chelating reagents for some metal ions. It

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has been used as a complexing agent for preconcentration metal ions on activated carbon

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(AC) (Mikula, & Puzio, 2007), silica gel (SG) (Mikula, Puzio, & Feist, 2009), carboxylic acid

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(COOH) bonded to silica gel (Mikula, Puzio, & Feist, 2009) and alumina (Shabani,

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Dadfarnia, & Dehghani, 2009). Abovementioned techniques are not selective. The use of ox-

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CNTs and 1,10-phenantroline enabled the selective determination of Pb(II) in the presence of

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coexisting ions. The key novelty in the study is the adsorption of cationic metal chelates with

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1,10-phenantroline on the surface of ox-MWCNTs. Until now methods based on the

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adsorption of metal ions on the surface of oxidized carbon nanotubes (ox-CNTs) by chelating

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complexes (inner chelates) have been presented. No information was found about application

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of ionic complexes, i.e. cationic complexes for metal ions preconcentration on the surface of

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the CTNs. The application of chelating agent is one of the method that can be used for the

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enhancement of the method selectivity.

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The aim of the work is to show the possibility of the usage of ox-MWCNTs for the dispersive

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micro solid phase extraction of traces and ultratrace lead(II) as 1,10-phenanthroline chelates

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and to application of the presented preconcentration procedure prior to their F-AAS and ET-

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AAS determination of food samples (fish).

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In conventional SPE, the liquid sample is passed through a column containing an adsorbent

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that retains the metal ions. However, the practical application of the CNTs in SPE can be

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hampered. Small particles of CNTs can cause high pressure in the SPE system. For these

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reason, CNTs was applied in dispersive micro-solid phase extraction (DMSPE) rather than in

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conventional SPE. In this case, the suspension of nanomaterial is injected into the analyzed

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aqueous sample. DMSPE promotes immediate interaction between the metal chelates and

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MWCNTs and shortens time of sample preparation in comparison with classical solid-phase

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extraction. In addition, there is a high dispersibility of the CNTs which increases the contact

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area of the CNTs with sample.

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2. Experimental

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2.1. Apparatus

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A flame and electrothermal atomic absorption spectrometer Solaar M6, (TJA

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Solutions, Cambridge, UK) equipped with a hollow cathode lamp (HCL) was used for

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determination of Pb. The wavelength was 217.0 nm. The F-AAS was equipped with a

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deuterium arc background correction and an air-acetylene burner. The ET-AAS was equipped

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with a Zeeman background corrector, an electrothermal atomizer and an autosampler. The

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furnace temperature program was applied: drying – 100 °C, pyrolisis – 800 °C, atomization –

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1200 °C and cleaning – 2500 °C. Aliquots of 20 µL were injected directly into the graphite

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tube pyrolytically coated (Schunk Kohlenstofftechnik, Germany). The analysis was performed

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using 5 µL of Mg(NO3)2 as chemical modifier. All instrumental parameters were adjusted

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according to the recommendations of manufacturer.

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A UniClever microwave mineralizer (Plazmatronika BM-1z, Poland) was used for dissolution of the food samples.

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2.2. Reagents and solutions

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All chemicals were of analytical reagent grade. The reagents were dissolved and

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diluted with high purity water obtained from a Milli-Q system (Millipore, Molsheim, France).

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The following reagents were used in the experiment: 1,10-phenanthroline, nitric acid,

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hydrochloric acid, sodium hydroxide, ammonia, nitrates(V) of sodium, potassium,

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magnesium, calcium, strontium, barium, aluminum, iron(III), manganese, cadmium, cobalt,

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copper, nickel, and zinc (all from POCh, Gliwice, Poland), nitric acid Suprapure (Merck,

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Darmstadt, Germany), stock standard solution of lead with concentration of 1000 mg L–1

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(Merck, Darmstadt, Germany), multiwalled carbon nanotubes with diameters 6-9 nm and

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lengths of ca. 5 µm (Sigma-Aldrich, Steinheim, Germany). Borate buffer solution was

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prepared by adding an appropriate amount of boric acid to disodium tetraborate solution until

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pH 7 was obtained. The accuracy of the method was assessed by analyzing the certified

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reference material (CRM): DOLT-3 (Dogfish Liver) supplied by the National Research

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Council of Canada (NRCC), Ottawa, Canada, and ERM – BB186 ( Pig Kidney) supplied by

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the Joint Research Centre, Institute for Reference Materials and Measurements, Geel,

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Belgium.

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2.3. Procedures

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2.3.1. Synthesis of oxidized multiwalled carbon nanotubes (ox-MWCNTs) and preparation of

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them suspension

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2 g of multiwalled carbon nanotubes MWCNTs were suspended in 100 mL of

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concentrated HNO3 and refluxed for 6 h at 100 °C. Finally, the mixture was filtered and

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washed with deionized water until pH of filtrate was 7. The filtered solid was dried in an oven

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at 60 °C. The suspension of ox-MWCNTs (5 mg mL-1) was prepared using high purity water.

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Before the use, the ox-MWCNTs suspension was sonicated for 30 min to obtain a

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homogeneous dispersion.

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2.3.2. Preconcentration of Pb(II) by a dispersive solid phase extraction procedure

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5 mL of 0.01 mol L–1 solutions of 1,10-phenanthroline and 0.2 mL of 5 mg mL–1

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suspension of ox-MWCNTs were added to 100 mL of analized solution. The pH value of the

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solution was adjusted to 7 using the borate buffer. Next, the mixture was stirred with a

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magnetic stirrer for 10 min to facilitate adsorption of the metal ions onto the sorbent. After

141

that, the sample was filtered through a paper filter. The adsorbed Pb(II) was eluted with 2 mL

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of 0.5 mol L–1 HNO3, at a flow rate of 2 mL min–1. The Pb(II) ions in the eluent were

143

determined by F-AAS or ET-AAS. Every experiment was repeated at three times.

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2.3.3. Preparation of real samples

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Certified reference material. 0.5 g of the certified reference material DOLT-3 (Dogfish

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liver) and 0.25 g of Pig Kidney (ERM - BB186) were digested in 6 mL of concentrated nitric

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acid using a microwave mineralizer (time: 10 min, power: 100%, max. pressure 45 atm).

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Microwave-assisted digestion of the sample was performed in closed 100 mL vessels. After

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cooling, the obtained solution was diluted to a volume of about 50 mL. Next, the sample was

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prepared using the preconcentration procedure. The same procedure was used for the blank

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solutions.

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Fish samples. The fish were bought from local supermarket in Poland. The fish stored

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at -20 °C prior analysis. Then the muscle fishes were separated and freeze-dried. For lead

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analysis 0.5 g of the samples was digested in 6 mL of concentrated nitric acid using a

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microwave mineralizer (time: 10 min, power: 100%, max. pressure 45 atm).

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digested samples were diluted to a final volume of 50 mL with deionised water, and Pb(II)

158

ions were preconcentrated using the DMSPE procedure described above.

Next, the

159 160

3. Results and discussion

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In this paper, trace amounts of Pb(II) ions were preconcentrated using ox-MWCNTs

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as an adsorbent and 1,10-phenanthroline as a chelating agent. In order to obtain high recovery

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of the Pb(II) ions on ox-MWCNTs, the procedure was optimized for various analytical

164

parameters such as pH, amount of mass sorbent, amount of 1,10-phenanthroline, stirring time,

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elution conditions such as volume and concentration of eluent and sample volume.

166 167

3.1. Effect of pH

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In a preliminary study, sorption of numerous elements such as Cd(II), Co(II), Cu(II),

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Fe(III), Mn(II), Ni(II), Pb(II), and Zn(II) was examined. The metal ions complexed with 1,10-

170

phenanthroline may be adsorbed on ox-MWCNTs by the electrostatic interactions, and due to

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the van der Waals forces. The adsorption of the metal ions - 1,10-phenanthroline cationic

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complex on ox-MWCNTs was investigated at pH from 2 to 11. As shown in Fig.1a, only the

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sorption of Pb(II) increases quickly at pH 3 – 6, and remains constans at pH 6 – 11. The

174

differences between results were not statistically significant (α = 0.05, f = n1+ n2 - 2 = 3+3-2

7

175

= 4, n = 3, tcrit = 2.77) in the given pH range (e.g. the recovery of Pb(II) was 95 ± 2, 99 ± 2,

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and 95 ± 2 for pH = 6, 7, and 11, respectively). The pH 7 was chosen as the optimum pH for

177

further determination of Pb(II). At the pH Mn(II) ions could be adsorbed below 50%, Cd(II)

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and Zn(II) ions could be adsorbed below 25%, but Fe(III), Co(II), Cu(II), Ni(II) ions could be

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adsorbed below 10%. These metal ions did not interfere with enrichment and determination of

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Pb(II) (discussed in section of effects of sample matrix). The results obtained for Cd(II),

181

Co(II), Cu(II), Fe(III), Mn(II), Ni(II), and Zn(II) was not reproducible.

182 183

3.2. Effect of mass of the sorbent

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The amount of the MWCNTs has influence on the contact between the sample

185

solution and the surface of the sorbent. Therefore, a suitable amount of the MWCNTs is a

186

crucial issue in sorption. In order to choose appropriate amount of sorbent, a series of

187

experiments were performed by varying the mass of ox-MWCNTs within the 0.25-1.25 mg

188

range. The results are given in Fig.1c. The results showed that quantitative adsorption for

189

Pb(II) was obtained in range of 0.75-1.25 mg. 1.0 mg of ox-MWCNTs was chosen as the

190

optimum mass for further study. Quantitative adsorption was not obtained when mass of the

191

sorbent was lower than 0.75 mg. The differences between recoveries were not statistically

192

significant (α = 0.05, n = 3, tcrit = 2.776) in the given mass of the sorbent range (e.g. the

193

recovery of Pb(II) was 99 ± 1.5, 100 ± 1, and 99 ± 1 for 0.75, 1.00, and 1.25 mg,

194

respectively).

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3.3. Effect of amount of 1,10-phenanthroline

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An appropriate amount of 1,10-phenanthroline should be carefully selected and used

198

to ensure the effective complexation of Pb(II) ions and to obtain the high recovery. The

199

studied range of 1,10-phenanthrolie amount was 0-15 mL of 0.01 mol L–1 solutions. The

8

200

results are given in Fig.1d. The recovery of Pb(II) on nanotubes was not quantitative without

201

1,10-phenanthrolie. Quantitative recoveries were obtained for Pb ion in the range 2-15 mL.

202

The optimum amount of 1,10-phenanthrolie was taken as 5 mL of 0.01 mol L–1 solutions for

203

further experiments. The differences between samples were not statistically significant (α =

204

0.05, n = 3, tcrit = 2.776) in the range of 2-10 mL of 1,10-phenanthroline (e.g. the recovery of

205

Pb(II) was 98 ± 1.5, 100 ± 1, and 95 ± 3 for 2, 5 and 10 mL, respectively).

206 207

3.4. Effect of stirring time

208

The stirring time of an analyte solution with oxidized MWCNTs can influence the

209

efficiency of the preconcentration of analytes. The stirring time of the solution in the range of

210

10–120 min does not play a significant role in the preconcentration of the determined metal

211

ions using the procedure. The recoveries of analytes are close to 100% even after 10 min of

212

stirring, which can indicate that the adsorption process is very quick and the reaction between

213

metal ions and functional groups of oxidized MWCNTs is immediate. Therefore, the stirring

214

time of 10 min was chosen as the adsorption equilibrium time. The differences between

215

results were not statistically significant (α = 0.05, tcrit = 2.776, n = 3) in the given stirring time

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range (e.g. the recovery of Pb(II) was 98 ± 2, and 97 ± 1 for 10 and 120 min, respectively).

217 218

3.5. Elution

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The final stage of DMSPE involves the elution of the metal ions. Influences of various

220

eluents given in Fig.1b on the recovery of retained Pb(II) on ox-MWCNTs were also studied

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at the optimal working conditions. Quantitative recoveries (>95 %) was obtained with 0.5 and

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1.0 mol L–1 HNO3. Further studies was carried out with 0.5 mol L–1 nitric acid.

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The volume of the eluent is important for the high concentration factor. This was examined by

224

2.0, 5.0 and 10 mL of 0.5 mol L–1 HNO3. The smallest volume of 0.5 mol L–1 HNO3 for the

225

quantitative elution was found to be as 2.0 mL.

226

The flow rate of the sample solution not only affects the recoveries of analytes, but also

227

controls the analysis time. The effect of the flow rate of the eluent solution on desorption of

228

Pb(II) from the sorbent surface was studied in the range of 0.5-5 mL min–1. Pb ions were

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completely desorbed at an eluent flow rate of less than 3 mL min–1, with effective and

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quantitative elution. However, a flow rate of 2 mL min–1 was chosen for future studies.

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3.6. Maximum sample volume and enrichment factor The sample volume is one of the most effective analytical variables for obtaining high

234

preconcentration factors and maximum applicable volumes in preconcentration studies. 50-

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500 mL aliquots of the model solutions containing trace Pb(II) were preconcentration under

236

the optimum conditions. It was found that quantitative recoveries (> 90%) were obtained for

237

sample volumes up to 400 mL for AAS and 200 mL for ET-AAS. Consequently, by

238

considering the final elution volume of 2.0 mL of 0.5 mol L–1 HNO3, the enrichment factor

239

using this method was 200 for F-AAS and 100 for ET-AAS. T-test was performed in order to

240

verify if average value of recovery of Pb(II) for sample volume to 100 mL (99 ± 2) and

241

average value of recoveries of Pb(II) for sample volume to 400 mL (95 ± 3) are significantly

242

different. The differences between samples were not statistically significant. (α = 0.05, n = 3,

243

tcrit = 2.776, t = 1.922).

244 245

3.7. Effect of foreign ions

246

In order to selectivity of proposed method, the effect of different cations on the

247

preconcentration and determination of Pb(II) ions were studied under optimal conditions.

10

248

Under the optimum conditions, a solution of 1.0 µg mL–1 of Pb ions and interference ions

249

were analyzed. Both influence of single elements and of the whole matrix on the recovery

250

were studied (Feist & Mikula, 2014). This results show that the presented procedure could be

251

applied to the multi-element separation and preconcentration of heavy metals. T-test was

252

performed in order to verify if average value of recovery of Pb(II) and average value of some

253

foreign ions on the recoveries of Pb(II) are significantly different. The results are presented in

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Table 1. According to T-student test, the differences between samples were not statistically

255

significant.

256 257

3.8. Validation and application of the method

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The Table 2 presents the analytical performance of the optimized method, including

259

the calibration range, limits of detection (LOD), limits of quantification (LOQ), recovery and

260

relative standard deviations (RSD). The LOD as well as LOQ were calculated as the

261

concentration corresponding to three or ten times the standard deviation σ of 10 runs of the

262

blank samples. The RSD of the ten replicate determinations are lower than 3.0% what

263

indicates that the method has a good precision for the analysis of traces and ultratrace of Pb in

264

solution samples (Feist & Mikula, 2014).

265

The method was validated by analysis of a certified reference material: DOLT-3 for F-AAS,

266

and ERM - BB186 for ET-AAS. T-test was performed in order to verify if average value and

267

certified value are significantly different. The results are presented in Table 3. According to

268

T-student test, the differences between samples were not statistically significant.

269

Then, the method has been applied for determination of Pb ion in fish samples by F-AAS and

270

ET-AAS. For the analysis of fish samples, the standard addition method was used and the

271

results are listed in Table 4. A reasonable consistence was obtained between the added and

272

measured lead amounts.

11

273 274

3.9. Adsorption capacity

275

Adsorption capacity is an important parameter for evaluation of an adsorbent, because

276

it determines how much sorbent is required for quantitative enrichment of the analyte from a

277

given solution. The sorption isotherm of Pb(II) ions at their initial concentration range of 5-70

278

mg L–1. The amount of metal ions adsorbed on ox-MWCNTs (mg g−1) was calculated from

279

the difference between the initial concentration C0 (mg L−1) and the equilibrium concentration

280

Ce (mg L−1) determined by F-AAS after filtration: q e = [(C0 – Ce)V]/m, where: V is the

281

volume of metal ion solution, and m is the mass of ox-MWCNTs. The capacity of the sorbent

282

for Pb(II) was found to be about 350 mg g–1.

283 284

4. Conclusions

285

In the present study, modified ox-MWCNTs with 1,10-phenanthroline showed good

286

adsorption and desorption properties with respect to Pb(II) ions as dispersive micro solid

287

phase extraction. The experiments show that ox-MWCNTs with 1,10-phenanthroline is

288

characterized by high selectivity toward Pb(II) ions at pH 7. Rapid adsorption equilibrium,

289

easy elution and high adsorption capacity were their good characteristics. Moreover, the new

290

adsorbent was successfully applied to the separation and preconcentration of trace amount of

291

Pb(II) ions from aqueous solutions without significant interference from other cations. In

292

summary, the adsorbent possessed high analytical potential for preconcentration of trace

293

Pb(II) ions from biological samples. In this work, the ox-MWCNTs with 1,10-phenanthroline

294

was used for selective and sensitive determination of Pb(II) ions by F-AAS and ET-AAS

295

using DMSPE. The developed methodology is characterized by extremely low LOD (6.4 ng

296

L-1) for ET-AAS. As it results from the data, ox-MWCNTs modified 1,10-phenanthroline has

297

a very high capacity compared to other methods reported in Table 5. The analytical procedure

12

298

based on DMSPE that required 1,10-phenanthroline and CNTs is significantly better over

299

other adsorbents, e.g. activated carbon and silica gel using 1,10-phenanthroline as complexing

300

agent. Obtained significantly lower detection limits and used significantly lower

301

concentrations of the eluent.

302 303 304

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Hu, Z.-J., Cui, Y., Liu, S., Yuan, Y., & Gao, H.-W. (2012). Optimization of ethylenediaminegrafted multiwalled carbon nanotubes for solid-phase extraction of lead cations. Environmental Science and Pollution Research, 19, 1237-1244. Yang, B., Gong, Q., Zhao, L., Sun, H., Ren, N., Qin, J., Xu, J., & Yang, H. (2011). Preconcentration and determination of lead and cadmium in water samples with a MnO2 coated carbon nanotubes by using ETAAS. Desalination, 278, 65–69. Kosanovic, M., Adem, A., Jokanovic, M., & Abdulrazzaq, Y.M. (2008). Simultaneous determination of cadmium, mercury, lead, arsenic, copper, and zinc in human breast milk by ICP-MS/microwave digestion. Analytical Letters, 41, 406–416. Mikula, B., & Puzio, B. (2007). Determination of trace metals by ICP-OES in plant materials after preconcentration of 1,10-phenanthroline complexes on activated carbon. Talanta, 71, 136-140. Mikula, B., Puzio, B., & Feist, B. (2009). Preconcentration of Cd(II), Pb(II), Co(II), Ni(II), and Cu(II) by solid-phase extraction method using 1,10-phenanthroline. Journal of Analytical Chemistry, 64, 786-790 Mikula, B., Puzio, B., & Feist, B. (2009). Application of 1,10-phenanthroline for preconcentration of selected heavy metals on silica gel. Microchimica Acta, 166, 337341. Mohammadi, S.Z., Afzali, D., & Pourtalebi, D. (2010). Flame atomic absorption spectrometric determination of trace amounts of lead, cadmium and nickel in different matrixes after solid phase extraction on modified multiwalled carbon nanotubes. Central European Journal of Chemistry, 8, 662-668. Mohammadi, S. Z., Shamspur, T., Karimi, M. A., & Naroui, E. (2012). Preconcentration of trace amounts of Pb(II) ions without any chelating agent by using magnetic iron oxide nanoparticles prior to ETAAS determination. The Scientific World Journal, 640437, 16. Nabida, MR., Sedghia, R., Bagheria, A., Behbahania, M., Taghizadeha, M., Oskooieb, HA., & Heravi, MM. (2012). Preparation and application of poly(2-amino thiophenol)/MWCNTs nanocomposite for adsorption and separation of cadmium and lead ions via solid phase extraction. Journal of Hazardous Materias, 203– 204, 93– 100. Parodi, B., Savio, M., Martinez, L.D., Gil R.A., & Smichowski, P. (2011). Study of carbon nanotubes and functionalized-carbon nanotubes as substrates for flow injection solid phase extraction associated to inductively coupled plasma with ultrasonic nebulization. Application to Cd monitoring in solid environmental samples. Microchemical Journal, 98, 225-230. Ruijun, L., Xijun, Ch., Zhenhua, L., Zhipeng, Z., Zheng, H., Dandan, L., & Zhifeng, T. (2011). Multiwalled carbon nanotubes modified with 2-aminobenzothiazole modified for uniquely selective solid-phase extraction and determination of Pb(II) ion in water Samales. Microchimica Acta 172, 269–276. Savioa, M., Parodi, B., Martinez, L.D., Smichowski, P., & Gil, R.A. (2011). On-line solid phase extraction of Ni and Pb using carbon nanotubes and modified carbon nanotubes coupled to ETAAS. Talanta, 85, 245–251. Shabani, A.M.H., Dadfarnia, S., & Dehghani, Z. (2009). On-line solid phase extraction system using 1,10-phenanthroline immobilized on surfactant coated alumina for the flame atomic absorption spectrometric determination of copper and cadmium. Talanta, 79, 1066-1070. Sitko, R., Gliwinska, B., Zawisza, B., & Feist, B. (2013). Ultrasound-assisted solid-phase extraction using multiwalled carbon nanotubes for determination of cadmium by flame

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Tables Table 1 Influences of some foreign ions on the recoveries of Pb(II) Table 2 Specification of presented method at optimum conditions for lead (n = 10) and results of analysis F-AAS and ETAAS methods after preconcentration Table 3 Analysis of certified reference material by FAAS and ETAAS. Results in mg kg-1 (n = 3) Table 4 Determination of Pb(II) in spiked fish samples (n = 4) Table 5 Comparative studies on Pb preconcentration Figure Fig.1. Optimalization of DMSPE procedure: a) effect of pH on adsorption of the elements studied; b) influences of some eluents on the recoveries of the lead; c) effect of amount of sorbent on the recoveries of the lead; d) effect of amount of 1,10-phenanthroline on the recoveries of the lead.

16

465 466 467 468 469

Fig. 1

17

470 471 472

Table 1 Influences of some foreign ions on the recoveries of Pb(II) (n = 3) Ions Amount (µg mL-1) Recovery (%) Pb Na K Mg Ca Ba Sr Al Cr Cd Co Cu Ni Zn Fe Mn All

2000 2000 1000 2000 100 100 500 5 20 20 20 20 20 100 100

99 ± 2 94 ± 3 97 ± 0.4 100 ± 4 91 ± 5 96 ± 3 102 ± 4 96 ± 3 100 ± 2 97 ± 2 92 ± 4 94 ± 3 99 ± 1 101 ± 2 99 ± 2 95 ± 4 99 ± 3

T-student test, α = 0.05, tcrit = 2.776 2.402 1.698 0.387 2.573 1.441 1.162 1.441 0.612 1.225 2.711 2.402 0.000 1.225 0.000 1.549 0.000

473 474 475 476 477

Table 2 Specification of presented method at optimum conditions for lead (n = 10) and results of analysis F-AAS and ETAAS methods after preconcentration Parameters Calibration range Preconcentration factor LOD (3σ) LOQ (10σ) Recovery (%) RSD (%) Equation Correlation coefficient

FAAS 2.0 – 25.0 (µg L-1) 200 0.26 (µg L-1) 0.87 (µg L-1) 99 ± 2.3 2.6 Abs = 0.0193xC+0.0020 0.9998

ETAAS 20.0 – 200.0 (ng L-1) 100 6.4 (ng L-1) 21.3 (ng L-1) 97 ± 2.7 2.9 Abs = 0.0121xC+0.032 0.9984

478 479 480 481 482

18

483 484 485

Table 3 Analysis of certified reference material by FAAS and ETAAS. Results in mg kg-1 (n = 3) Sample

Certified (mg kg-1)

DOLT-3

0.32 ± 0.05

ERM - BB186

0.040 ± 0.005

Found (mg kg-1)

Relative differences (%) FAAS 0.33 ± 0.05 3.1 ETAAS 0.039± 0.008 2.5

T-student test. α = 0.05. tcrit = 4.303

t = 0.346 t = 0.216

486 487 488 489

Table 4 Determination of Pb(II) in spiked fish samples (n = 4) Sample

Added (mg kg-1)

Found (mg kg-1)

Cod tissue

0 2 5 0 2 5

2.92 ± 0.13 4.87 ± 0.09 7.86 ± 0.06 4.16 ± 0.09 6.11 ± 0.04 8.96 ± 0.18

Herring tissue 1

Herring tissue 2

0 0.05 0.1

RSD (%)

FAAS 4.45 1.8 0.76 2.2 0.65 2.0 ETAAS 0.072 ± 0.006 8.3 0.120 ± 0.010 8.3 0.169 ± 0.010 5.9

Recovery (%)

97.5 98.8 97.7 96.0 96.0 97.0

490 491 492 493 494 495 496 497 498 499 500 501 502 503 504

19

505

Table 5. Comparative studies on Pb preconcentration SPE sorbent

Eluent

PF

LOD (µg L1 ) 0.0044

Detection method

Reference

100

Sorption capacity (mg g-1) 6.7

MnO2/CNTs composite

1.5 mol L-1 HNO3 0.1 mol L-1 HCl

ET-AAS

Yang et al, 2011

100

-

0.01

ET-AAS

2 mol L-1 HNO3

100

96

0.009

ET-AAS

Ionic imprinted polymer

2 mol L-1 HNO3

12.5

-

0.49

ET-AAS

Magnetic Fe3O4 nanoparticles

1 mol L-1 HNO3

200

28.6

0.0008

ET-AAS

MWCNTs-1,10phenanthroline Polyhydroxybutyrateb-polyethyleneglycol

0.5 mol L-1 HNO3 1 mol L-1 HCl

100

350

0.0064

ET-AAS

Savioa, Parodi, Martinez, Smichowski, & Gil, 2011 Sitko, Janik, Feist, Talik, & Gagor, 2014 Barciela-Alonso, Plata-Garcia, Rouco-Lopez, Moreda-Pineiro, & Bermejo-Barrera, 2014 Mohammadi, Shamspur, Karimi, & Naroui, 2012 This paper

GO-NH2

50

19.6

1.82

F-AAS

MWCNT-bis(5bromosalicylidene)1,3-propandiamine

2 mol L-1 HNO3

100

-

2.63

F-AAS

1-(2-Pyridylazo)-2naphthol nanoporous silica MWCNT-3-hydroxy-4((3-silylpropylimino) methyl) phenol

HCl:HNO3 1:1 (mol L−1)

280

210

0.9

F-AAS

4 mol L-1 HNO3

17.9

36.8

2.89

F-AAS

MWCNT- Schiff’s base AC-1,10phenanthroline

1 mol L-1 HNO3 3 mol L-1 HNO3 (static method) 8 mol L-1 HNO3 (dynamic method) 3 mol L-1 HNO3 3 mol L-1 HNO3 0.5 mol L-1 HNO3

21.5

18

1.8

F-AAS

100 50

-

70.8

ICP-OES

100

-

10.8

ICP-OES

80

-

17.5

ICP-OES

200

350

0.26

F-AAS

MWCNTs-L-Alanine

SG-1,10phenanthroline SG-COOH-1,10phenanthroline MWCNTs-1,10phenanthroline

Wadhwa, Tuzen, Kazi, Soylak, & Hazer, 2014 Ghaedi, Mokhtari, Montazerozohori, Asghari, & Soylak, 2014 Abolhasani, & Behbahani, 2015 Ghaedi, Montazerozohori, Rahimi, & Biysreh, 2013 Dalali, Ashouri, & Nakisa, 2012 Mikula, & Puzio, 2007

Mikula, Puzio, & Feist, 2009 Mikula, Puzio, & Feist, 2009 This paper

506

20

507 508

Modified ox-MWCNTs using 1,10-phenanthroline as a selective sorbent in DMSPE

509

High capacity and small LOD found using cationic chelate complex with 1,10-phenanthroline

510

Using F-AAS and ET-AAS for the determination of Pb(II)

511

Application to determination of lead content of fish samples

512 513 514

21