Determination of ultra-trace palladium (II) in water, soil, and food samples by dispersive liquid‐liquid microextraction-atomic absorption spectrometry using 2-mercaptobenzimidazole as a complexing agent

    Determination of Ultra-trace palladium (II) in water, soil and food samples by dispersive liquid–liquid microextraction-atomic absorbtion spectrometry using 2-mercaptobenzimidazole as a complexing agent Mohsen Pouyan, Ghadamali Bagherian, Nasser Goudarzi PII: DOI: Reference:

S0026-265X(16)00024-2 doi: 10.1016/j.microc.2016.02.003 MICROC 2408

To appear in:

Microchemical Journal

Received date: Revised date: Accepted date:

26 June 2015 5 February 2016 5 February 2016

Please cite this article as: Mohsen Pouyan, Ghadamali Bagherian, Nasser Goudarzi, Determination of Ultra-trace palladium (II) in water, soil and food samples by dispersive liquid–liquid microextraction-atomic absorbtion spectrometry using 2mercaptobenzimidazole as a complexing agent, Microchemical Journal (2016), doi: 10.1016/j.microc.2016.02.003

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Mohsen pouyan, Ghadamali Bagherian*, Nasser Goudarzi

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Determination of ultra-trace palladium (II) in water, soil and food samples by dispersive liquid-liquid microextraction-atomic absorbtion spectrometry using 2mercaptobenzimidazole as a complexing agent

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College of Chemistry, Shahrood University of Technology, Shahrood, P.O. Box 36155-316, Iran

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Corresponding author Tel: +98 23 32395441

E-mail: [email protected]

ACCEPTED MANUSCRIPT ABSTRACT A new, simple, and rapid method was developed for selective extraction and determination of trace levels of Pd(II) by dispersive liquid-liquid microextraction (DLLME)

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preconcentration and flame atomic absorption spectrometry detection. In the developed

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method, 2-mercaptobenzimidazole (MBI) was used as a Pd(II) complexing agent. Chloroform and acetone were selected as the extraction and dispersive solvents, respectively. The

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effective DLLME parameters such as pH, kinds of extraction and dispersive solvents and their volumes, concentration of the complexing agent, and extraction time were studied and optimized. Under the optimum experimental conditions, the calibration graph was linear over

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the range of 15-1100 µg L−1 with a detection limit (3σ) of 8 µg L−1 for palladium(II). The relative standard deviations (RSDs, n = 6) were lower than 4.8%. The enhancement factor

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was obtained to be 20.7. This environmentally-friendly method was successfully applied to the determination of trace levels of palladium(II) in soil, food, and spiked waterfall and tap water samples. The accuracy the developed method was also evaluated by the analysis of the

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certified reference material GPP-10.

Keywords: Palladium, Dispersive liquid-liquid microextraction, Atomic absorption

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spectrometry, 2-Mercaptobenzimidazole.

ACCEPTED MANUSCRIPT 1. Introduction Palladium has been widely used in dental and medicinal devices, jewelry, electrical products, and electronics and catalytic converters [1-4]. In the last few years, the catalytic

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converters containing platinum, palladium and rhodium used for reducing emission of

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gaseous pollutants such as carbon monoxide, nitrogen oxides, and hydrocarbons have resulted in an increasing concentration of platinum group elements (PGEs) in environmental

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matrices, especially in the roadside dusts, soils, and plants. Palladium has a strong catalytic activity in the hydrogenation, dehydrogenation, oxidation, and hydrogenolysis reactions. Several palladium salts may cause severe primary skin and eye irritations. Palladium(II) ions

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have been shown to be potent skin sensitizers. The epidemiological studies have demonstrated that palladium(II) ions are among the most frequent sensitizers within metals.

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Dental alloys and jewelry are possible sources of palladium sensitization in the general population [5-8]. Palladium salts have been found to be very toxic to the aquatic plants even at very low concentrations [9, 10]. The development of analytical methods for determination

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of palladium(II) is important for the effective monitoring of pollution levels of this metal ion

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in the environment.

Different kinds of conventional analytical techniques such as electrothermal atomic

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absorption spectrometry (ETAAS) [11-19], flame atomic absorption spectroscopy (FAAS) [20-24], inductively-coupled plasma atomic emission spectrometry (ICP-OES) [25, 26], inductively coupled plasma mass spectrometry (ICP-MS) [27, 28], neutron activation analysis (NAA) [29], and UV-visible spectrophotometry [18, 30-33] have been used for the

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determination of palladium.

In the environmental samples, a low concentration of Pd(II) (at µg L−1 levels) together with a high concentration of interfering matrix components often requires an enrichment step combined with a matrix separation that allows an accurate and a precise determination of Pd(II) in samples with very low analyte contents [17]. Several methods such as co-precipitation [23], solid-phase extraction [34-36], liquidliquid extraction [37, 38], and cloud point extraction [26, 39, 40] have been reported for the separation and preconcentration of palladium ions but the disadvantages such as timeconsumption, unsatisfactory enrichment factors, and large organic and secondary wastes have limited their applications. In order to overcome these problems, the microextraction methods such as homogenous liquid-liquid microextraction [41, 42], single-drop microextraction [43, 44], solid-phase microextraction [45], and DLLME [11-13, 16-21, 46, 47] have been developed for the preconcentration of organic and inorganic species. In the DLLME method,

ACCEPTED MANUSCRIPT an appropriate mixture of the solvent and dispersive solvent is injected into an aqueous sample rapidly by a syringe, as a result of which, a cloudy solution is formed. The analyte in the sample is extracted into fine droplets of the extraction solvent. After extraction, phase

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separation is performed by centrifugation, and the enriched analyte in the sediment phase is

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determined by chromatography or spectrometry methods. The advantages of the DLLME method are simplicity of operation, low cost, rapidity, high recovery, and enrichment factors.

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This method has been successfully applied for the preconcentration of organic [46-50] and inorganic [11-13, 16-21, 51-53] species in the environmental samples. The aim of this work is to combine DLLME with FAAS in order to develop a new

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method for the determination of trace amounts of palladium(II) in the environmental samples. In this method, 2-mercaptobenzimidazole (MBI) was used as a chelating agent, which formed

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a stable and hydrophobic complex with the palladium(II) ions [54]. The accuracy of the method was verified by analysis of a certified reference material (GPP-10). The proposed method was successfully applied to the determination of palladium(II) ions in soil, food, and

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spiked waterfall and tap water samples.

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2. Experimental

2.1. Reagents and solutions

All reagents were of analytical grade, and were used without further purification. All the

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solutions used were prepared using doubly distilled water. A 0.020 mol L−1 solution of MBI was prepared by dissolving 0.1502 g of MBI (Merck) in 50 mL of ethanol. The standard stock solution of palladium (10000 µg mL-1) for atomic absorption was purchased from Merck. The working standard solutions were prepared by diluting the appropriate volumes of the stock solution. A buffer solution of pH 5.0 was prepared by mixing 0.10 mol L-1 of acetic acid and 0.10 mol L-1 of sodium acetate solutions in an appropriate ratio and then adjusting the pH value of the resulting solution using a pH-meter. A phosphate buffer solution of pH 2.0 was prepared by mixing appropriate volumes of 0.10 mol L−1 of sodium dihydrogen phosphate and phosphoric acid solutions. Phosphate buffer solutions (H2PO4−/HPO42−) were prepared by mixing appropriate volumes of 0.10 mol L−1 of potassium dihydrogen phosphate and 0.10 mol L−1 of sodium hydrogen phosphate solutions for pH values of 3.0 to 7.0. A phthalate buffer solution of pH 5.0 was prepared by mixing 0.10 mol L-1 of potassium

ACCEPTED MANUSCRIPT hydrogen phthalate and 0.10 mol L-1 of sodium hydroxide solutions in an appropriate ratio and then adjusting the pH value of the resulting solution using a pH-meter.

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2.2. Apparatus

A Shimadzu UV-160 spectrophotometer with 1.0 cm quartz cell pairs was used to record

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the UV-visible spectra. A Shimadzu atomic absorption spectrometer (Model AA-670) equipped with an air–acetylene flame and palladium hollow cathode lamp was used for absorbance measurements at wavelength of 244.8 nm. The instrumental parameters were

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adjusted according to the manufacturer’s recommendations (Flame: air-acetylene, oxidizing; Flame height: 6 mm; Wavelength: 244.8 nm; Current: 4 mA; Slit: 0.2 nm). A Metrohm 744

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pH-meter was used for the pH measurements.

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2.3. General procedure

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8.0 mL of an aqueous sample solution containing the target analyte in the range of 15.01100 µg, 1.0 mL of acetate/acetic acid buffer solution (pH 5.0), and 60 µL of MBI (0.020

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mol L-1) (as the chelating agent) was placed in a 10-mL glass test tube with a conic bottom, and was diluted up to 10.0 mL with water. After rapidly and vigorously injecting 1.50 mL of acetone (as the dispersive solvent) containing 150 µL of chloroform (as the extraction solvent) into the sample solution using a 1.00 mL syringe, immediately, a cloudy solution

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was formed in the test tube. The mixture was gently shaken. In order to accelerate the phase separation, the cloudy solution was centrifuged for 5 min at 5000 rpm. As a result, the resulting dispersed fine droplets were sedimented at the bottom of the conical test tube, where they were collected using a Hamiltonian 100 µL syringe. The sedimented phase was quantitatively transferred into a 2-mL test tube, and the solvent was let to evaporate at 90 oC. Then the resulting solid residue was dissolved in 50 µL of acetone, and diluted to 400 µL with distilled water for the determination of Pd(II) by FAAS. The measurement was repeated in the absence of Pd(II) to obtain a blank signal. The difference between the absorbance of the sample and blank solutions (ΔA = As − Ab) at 244.8 nm was used as an analytical signal.

2.4. Sample preparation

ACCEPTED MANUSCRIPT Mojen waterfall and Shahrood pipe water samples were collected in acid-leached polyethylene bottles. The pH of the collected water samples were adjusted to 2 using nitric acid immediately after collection, in order to prevent adsorption of Pd(II) ions on the flask

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walls. The samples were filtered using Wattman filter papers before analyses.

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A soil sample was collected from around the Imam Reza Street in Mashhad (Iran).

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The sample was dried at 100 °C for 2 h and ground. 5.00 g of the soil sample or the certified reference material GPP-10 (kind of sample: reference ore, manufacturer: GEOSTATS PTY LTD, Australia) was transferred into a beaker. Then 15.0 mL of aqua regia was added, and the mixture was heated almost to dryness. In order to complete the digestion, again, 15.0 mL

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of aqua regia was added to the residual, and the mixture was heated almost to dryness. After cooling the sample mixture followed by addition of 20.0 mL of distilled water, it was filtered

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using a Wattman filter paper. The pH of the solution under the filter was adjusted to 2.0-3.0, and then it was transferred into a 100-mL volumetric flask, and diluted with water. A fresh garlic sample was dried for some days and in an oven at 45 oC to a constant

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weight. 2.500 g of the dried sample was transferred into a beaker, to which 10.0 mL of conc.

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HNO3 was added. It was placed on a hot plate to get semi-dried. Again, 10 mL of conc. HNO3 and 2 mL of H2O2 were added, and the solution was kept on the hot plate in order to

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complete the digestion. After getting dried, it was cooled, and 20 mL of water was added to it, and then it was filtered using a Wattman filter paper. The pH value for the sample solution was adjusted to 2.0-3.0, and then it was transferred into a 100-mL volumetric flask, and

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diluted with water.

3. Results and discussion In this work, a combination of DLLME with FAAS was developed for the determination of ultra-trace levels of palladium. It is based upon the complex formation between Pd(II) and MBI in aqueous phase and microextraction of the Pd(II)-MBI complex using acetone as the dispersive solvent and chloroform as the extraction solvent. Fig. 1 shows the absorption spectra of MBI and the Pd(II)-MBI complex in aqueous phase. The absorption maximum of MBI was at 298 nm, and that for the complex was at 365 nm. The absorption maximum of the Pd(II)-MBI complex (365 nm) with respect to MBI (298 nm) shows that MBI with Pd(II) forms complex. In the developed method, the Pd(II)-MBI complex is extracted into the extraction solvent. Immediately after each addition of the Pd(II) solution to MBI (as the

ACCEPTED MANUSCRIPT ligand solution), the yellow-colored complex Pd-MBI was formed. In addition, the effect of time on the completion of the reaction between Pd(II) and MBI was investigated, as follows. 1.0 mL of a Pd(II) solution (50.0 µg mL−1), 1.0 mL of an acetate buffer solution (pH 5.0), and

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300 µL of an MBI solution (0.010 M) were sequentially transferred to a 10.0-mL graduated

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flask, and a stopped clock was immediately started to monitor the reaction progress. This reaction mixture was made up to the mark of the graduated flask with doubly distilled water.

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After mixing, ca. 2 mL of this solution was transferred to a spectrophotometer cell, and the change in its absorbance was recorded at 365 nm against water for the first 30-900 s reaction time interval. The results obtained showed that the absorbance was constant within this time

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interval, which meant that the reaction between Pd(II) and MBI is very fast, and thus time did not have any effect on the amount of the complex formed.

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Preliminary experiments were carried out to identify the general features such as the diluting solvent and extraction solvent. In order to obtain a high extraction efficiency, the effects of different parameters affecting the complex formation and extraction conditions

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such as pH, concentration of the chelating agent, types of the disperser and extraction

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solvents and their amounts, extraction time, volume of sample solution, centrifugation time, and diluting solvent were investigated and optimized. The optimization was carried out on an

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aqueous solution containing 2.0 µg of palladium(II). The one-variable-at-a-time optimization methodology was applied to obtain the optimum conditions for the DLLME method.

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3.1. Effect of pH

It is well-known that the pH of the sample solution is one of the important factors affecting the state of complexes (as ions or neutral forms). The effect of pH on the DLLME method was studied over the pH range of 2.0-7.0 (phosphate buffer solutions). As it can be seen in Fig. 2, the maximum absorbance was achieved in the pH range of 4.0-6.0. In more acidic media, the formation of complex was incomplete owing to the protonation of chelating agent, while increasing pH above this optimum range caused a gradual decrease in the absorbance intensity probably due to the precipitation of palladium hydroxide. Therefore, pH 5.0 was selected for further studies. The influence of buffer type (pH 5.0) on the extraction performance was also investigated. In this study, the buffer solutions of pH 5.0 were prepared from acetate/acetic acid, citrate/citric acid, hydrogen phthalate/sodium hydroxide, and dihydrogen phosphate/hydrogen phosphate. The results obtained showed that the extraction

ACCEPTED MANUSCRIPT recoveries were in the range of 66.9%-71.1%, which was almost the same for all of them. The acetate buffer solution (pH 5.0) was selected for further studies because acetate ions had less

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interaction with cations than the other buffer ions.

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3.2. Selection of extraction solvent

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The type of extraction solvent used in the DLLME method is an important factor for an efficient extraction. The extraction solvent should be denser than water. Moreover, it should have more capability for the extraction of the compounds of interest and lower solubility in water. Thus chloroform, chlorobenzene, and carbon tetrachloride were studied as the

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extraction solvents for which, the extraction recoveries were obtained to be 71.1%, 46.5%, and 25.2%, respectively. A series of sample solutions were studied using 1.5 mL of acetone

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containing 120 µL of a different extraction solvent. The results obtained showed that the highest extraction recovery was achieved in the presence of chloroform. Therefore,

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chloroform was selected as the best extraction solvent for further experiments.

3.3. Selection of dispersive solvent

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The most important criterion in the selection of a dispersive solvent is that the solvent should form a cloudy state when injected with the organic extractant into an aqueous phase, besides having its solubility in the organic extracting solvent and the aqueous sample. On the

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other hand, the dispersive solvent should be soluble in the aqueous sample, and the extraction solvent should be soluble in the dispersive solvent. In order to seek the most suitable dispersive solvent, four kinds of dispersive solvents including acetonitrile, methanol, acetone, and ethanol were studied. In the investigation of this factor, a series of sample solutions were studied using a mixture containing 120 µL of chloroform and 1.38 mL of a different dispersive solvent. The extraction recoveries for acetonitrile, methanol, acetone, and ethanol were obtained to be 57.8, 40.9, 71.1, and 38.5%, respectively. Thus the maximum extraction recovery was obtained using acetone as the dispersive solvent. Hence, further experiments were performed using acetone as the dispersive solvent.

3.4. Effect of extraction solvent volume

ACCEPTED MANUSCRIPT Influence of the extraction solvent volume on the extraction performance was also investigated. The mixture containing 1.38 mL of the dispersive solution (acetone) and different volumes of chloroform in the range of 90-180 µl was subjected to the DLLME

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procedure. It was observed that the sediment phase volumes increased as the extraction

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solvent volume increased. As shown in Fig. 3, as the amount of chloroform increased, the extraction recoveries for the analyte initially increased until 140 µL and then remained

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constant up to 150 µL, and after that, slightly decreased. This is probably because the extraction solvent droplets that could not disperse well using the dispersive solvent caused low extraction efficiencies. Consequently, 150 µL was used as the optimum volume of the

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3.5. Effect of dispersive solvent volume

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extraction solvent.

Volume of the dispersive solvent is one of the key parameters in the DLLME procedure.

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This parameter directly affects the formation of the cloudy phase solution and the degree of

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dispersion of the extraction solvent in the aqueous phase, thus affecting the extraction recoveries. To obtain the optimized volume of the dispersive solvent, the volume of acetone

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was varied between 0.75 and 1.85 mL, while the volume of chloroform was kept constant (150 µL). The results obtained (Fig. 4) indicated that the extraction recoveries increased with increase in the acetone volume from 0.75 to 1.35 mL, and then remained constant up to 1.55 mL, and after that, slightly decreased. In volumes less than 1.35 mL of acetone, probably the

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extraction solvent droplets that could not disperse well using the disperser solvent caused low extraction efficiencies. In the acetone volumes greater than 1.55 mL, probably, the complex solubility in the aqueous phase increased, and thus the extraction efficiency decreased. Hence, 1.35 mL of acetone was chosen as the optimum volume for the dispersive solvent.

3.6. Effect of chelating agent concentration Concentration of the chelating agent is a critical factor to be optimized in the preconcentration methods for metal ions. In the investigation of this factor, the ethanol volume was kept constant (60 µL). The effect of MBI concentration in the range of 1.00 × 105

-1.50 ×10-4 mol L-1 on the microextraction of palladium(II) (0.20 µg mL−1) was studied. The

results obtained showed that the extraction efficiency for palladium(II) increased as the concentration of MBI increased from 1.00 × 10-5 to 4.00 × 10-5, and then remained constant

ACCEPTED MANUSCRIPT up to 1.50 × 10-4 mol L-1. Hence, 1.20 × 10-4 mol L−1 of MBI was taken as the optimal amount for the palladium(II) determination at high concentrations, and to prevent any

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interference.

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3.7. Extraction time and centrifugation time

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In DLLME, the extraction time is defined as the time interval between the injection mixture of the dispersive solvent and the extraction solvent, and before centrifugation. To investigate the effect of extraction time on the extraction efficiency of palladium(II), the

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extraction times 0.5, 1, 2, 5, and 10 min were studied under the optimum experimental conditions. The results obtained indicated that the extraction time had no influence on the

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extraction efficiency. Thus the extraction in DLLME is very fast. Keeping the rotation speed at 5000 rpm, the centrifugation time (2-10 min) was also studied. It was found that by increasing the centrifugation time to 4 min, the maximum

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analytical signal was observed, and then it was constant with a further increase in the

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centrifugation time. Therefore, 5 min was used for the centrifugation time throughout the

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study.

3.8. Ionic strength

To investigate the influence of the ionic strength on the microextraction system, various

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experiments were performed by adding different amounts of KNO3 (0.0-0.6 mol L-1), while the rest of the experimental conditions were kept constant. KNO3 was selected because nitrate ions have no interaction with Pd(II) ions, while sulphate and/or chloride ions, probably, interact with Pd(II). The results obtained showed that the addition of KNO3 within the interval of 0.0-0.6 mol L−1 had no considerable effect on the extraction efficiency. Therefore, all the extraction experiments were carried out without addition of the salt.

3.9. Sample volume and preconcentration factor To obtain a high preconcentration factor, the volume of sample solution is another important parameter that should be studied and optimized for the DLLME method. This parameter was studied in two states. In the first state, the concentration of Pd(II) was constant, and the influence of the volume of the sample solution (containing 0.20 µg mL−1 of

ACCEPTED MANUSCRIPT Pd(II)) on the recovery was investigated in the range of 5.0-10.0 mL. The experimental results obtained showed that the extraction efficiency of palladium was constant in the range of 8.0-10.0 mL, and for the lower sample volumes, the extraction efficiency decreased. In the

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second state, the number moles of Pd(II) was kept constant, and the influence of the volume

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of the sample solution (containing 2.0 µg of Pd(II)) on the recovery was investigated in the range of 5.0-10.0 mL. The experimental results also showed that the extraction efficiency of

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sample solution volume throughout the study.

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palladium was constant in the range of 8.0-10.0 mL. Therefore, 10.0 mL was used for the

3.10. Selectivity

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In view of the selectivity provided by AAS, possible interferences can mostly be attributed to the preconcentration step. In order to demonstrate the selectivity of the microextraction system developed for the determination of palladium(II), the effect of

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contaminant ions commonly found in environmental samples was evaluated. The study was

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performed by analyzing 10 mL of 0.2 mg L-1 of palladium(II) solution containing concomitant ions at different concentrations according to the recommended extraction

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procedure. A given species was considered to interfere if it resulted in a ±5% variation in the AAS signal. The results obtained (Table 1) showed that most of the cations and anions did not interfere with the extraction and determination of Pd(II). These results also indicated that a serious interference could arise due to the presence of the Cu2+ and Ag+ ions. The

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interference of Cu2+ ions could readily be overcome if citrate ion (5000 fold with respect to Pd2+), as the masking agent, was used. The interference of Ag+ ions was eliminated using I(5000 fold with respect to Pd2+) before addition of the MBI solution and before injection of the mixture of the dispersive and extraction solvents, and then centrifugation was performed to separate the resulting AgI precipitate. From the results obtained, it can be concluded that the method is free from the interferences of many foreign ions.

3.11. Figures of merit A calibration curve was obtained under the optimized experimental conditions with a linear dynamic range of 0.015-1.10 µg mL-1 with the regression equation A = 0.005 + 0.466CPd (r2 = 0.9998 for n = 10), where A is the analytical signal AAS and CPd is the Pd(II) concentration in µg mL-1. The limit of detection, defined as CL = 3SB/m (where CL, SB, and m

ACCEPTED MANUSCRIPT are the limit of detection, standard deviation of the blank signal, and slope of the calibration graph, respectively), was 8 µg L-1. The limit of quantification (LOQ), defined as CQ = 10SB/m (where CQ, SB, and m are the limit of quantification, standard deviation of the blank signal,

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and slope of the calibration graph, respectively), was 26 µg L-1. The precision of this method

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was determined by analyzing the standard solution at 20.0, 50.0. 200.0, 500.0, and 900.0 µg L-1 of Pd(II) for six times continuously, and the RSDs were 4.8, 2.9, 0.91, 0.42, and 0.26 %,

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respectively. The enhancement factor was obtained using the slope ratio of the calibration graph after and before the extraction, which was about 20.7. The method was found to be selective with a lower limit of detection and a wider linear dynamic range over other reported

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methods in the literature [17].

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3.12. Validity of the method

For evaluating the accuracy of the developed method, it was applied to determine

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Pd(II) in the reference ore sample (GPP-10 certified reference material). The measured

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concentration was 1993 ± 72 ng g−1 for Pd (n = 4; results given as the average and standard deviation). This result is in good agreement with the certified concentration value of 2008 ± 92 ng g-1 (the average and standard deviation). The statistical analysis of these results using

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the Student’s t-test showed that there was no significant difference between the actual and found concentrations at the 95% confidence level.

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To demonstrate the performance and applicability of the developed method, it was also utilized to extract and determine palladium(II) concentration in one soil, two water, and one food (garlic) samples. The recovery experiments were carried out by spiking the samples with different amounts of palladium(II) before any pretreatment. The results obtained were tabulated in Table 2. As it can be seen in this table, the recoveries between 97.2% and 103.0% were obtained, which confirmed the accuracy of the developed method.

4. Conclusion In this study, a simple, rapid, and inexpensive DLLME recovery and concentration method was developed and combined with FAAS for the determination of palladium(II). The optimum parameters for the extraction performance were evaluated.

ACCEPTED MANUSCRIPT The new DLLME-FAAS method was developed for the preconcentration and determination of Pd(II) in the certified reference material GPP-10, water, soil, and food samples. The method is inexpensive, and has a lower limit of detection and a wider linear

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dynamic range. The sample preparation time and consumption of toxic organic solvents are

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minimized in this method without affecting its sensitivity. Thus this method is an environmentally-friendly procedure. A satisfactory enrichment factor and good recoveries

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show the efficiency and applicability of this method for various samples. The developed method is a selective, rapid, sensitive, and an environmentally-friendly method for the trace

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analysis of Pd(II).

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Acknowledgment

The support of this investigation by the Shahrood University of Technology is gratefully acknowledged. We also acknowledge the beneficial help of Mr. Hassan Shariati, an

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ex-MsC student of this college, in carrying out this work.

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References

[1] T. Hees, B. Wenclawiak, S. Lustig, P. Schramel, M. Schwarzer, M. Schuster, D.

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Verstraete, R. Dams, E. Helmers,Comparison of palladium and platinum in environmental matrices: Palladium pollution by automobile emissions?, Environ. Sci. Pollut. Res. Int.5(1998) 105-111.

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[2] M. Krishna, M. Ranjit, K. Chandrasekaran, G. Venkateswarlu, D. Karunasagar,On-line preconcentration and recovery of palladium from waters using polyaniline (PANI) loaded in

Talanta79(2009)1454-1463.

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mini-column and determination by ICP-MS; elimination of spectral interferences,

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[3] N. Ozturk, V.N. Bulut, C. Duran, M. Soylak, Coprecipitation of palladium (II) with 1,5diphenylcarbazite–copper (II) and determination by flame atomic absorption spectrometry,

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Desalination 270(2011) 130-134.

[4] C. Rao, G. Reddi, Platinum group metals (PGM); occurrence, use and recent trends in their determination, TrAC, TrendsAnal. Chem.19 (2000) 565-586.

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[5] M. Augthun, M. Lichtenstein, G. Kammerer, Studies on the allergenic potential of palladium alloys, DeutschezahnarztlicheZeitschrift.45 (1990) 480-482. [6] C. Vincenzi, A. Tosti, L. Guerra, F. Kokelj, C. Nobile, G. Rivara, E. Zangrando, Contact dermatitis to palladium: a study of 2,300 patients, Dermatitis.6 (1995) 110-112. [7] K. Boch, M. Schuster, G. Risse, M. Schwarzer, Microwave-assisted digestion procedure for the determination of palladium in road dust, Anal. Chim. Acta 459 (2002) 257-265. [8] P. Castelain, M. Castelain,Contact dermatitis to palladium, ContactDermatitis.16 (1987) 46. [9] K. Leopold, M. Maier, S. Weber, M. Schuster, Long-term study of palladium in road tunnel dust and sewage sludge ash, Environ. Pollut.156 (2008) 341-347. [10] F. Battke, K. Leopold, M. Maier, U. Schmidhalter, M. Schuster, Palladium exposure of barley: uptake and effects,Plant Biol. 10 (2008) 272-276.

ACCEPTED MANUSCRIPT [11] P. Liang, E. Zhao, F. Li, Dispersive liquid–liquid microextraction preconcentration of palladium in water samples and determination by graphite furnace atomic absorption spectrometry, Talanta 77 (2009) 1854-1857.

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[12] P. Liang, E. Zhao, Determination of trace palladium in complicated matrices by

spectrometry, Microchim. Acta 174 (2011) 153-158.

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displacement dispersive liquid-liquid microextraction and graphite furnace atomic absorption

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[13]B. Majidi, F. Shemirani, Solvent-based de-emulsification dispersive liquid–liquid microextraction of palladium in environmental samples and determination by electrothermal atomic absorption spectrometry, Talanta 93 (2012) 245-251.

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[14] J. Chwastowska, W. Skwara, E. Sterlińska, L. Pszonicki, Determination of platinum and palladium in environmental samples by graphite furnace atomic absorption spectrometry after

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separation on dithizone sorbent, Talanta 64 (2004) 224-229. [15] G.Z. Tsogas, D.L. Giokas, A.G. Vlessidis, N.P. Evmiridis, On the re-assessment of the optimum conditions for the determination of platinum, palladium and rhodium in

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environmental samples by electrothermal atomic absorption spectrometry and microwave

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digestion, Talanta 76(2008) 635-641.

[16] M. Shamsipur, M. Ramezani, M. Sadeghi, Preconcentration and determination of ultra

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trace amounts of palladium in water samples by dispersive liquid-liquid microextraction and graphite furnace atomic absorption spectrometry, Microchim. Acta 166 (2009) 235-242. [17] T.Ahmadzadeh Kokya, K. Farhadi, Optimization of dispersive liquid–liquid microextraction for the selective determination of trace amounts of palladium by flame

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atomic absorption spectroscopy, J. Hazard. Mater. 169 (2009) 726-733. [18] H. Eskandari, In situ formed 1-hexyl-3-methylimidazolium hexafluorophosphate for dispersive liquid-liquid microextraction of Pd(II) prior to electrothermal AAS and spectrophotometry, Turk. J.Chem.36 (2012) 631-643. [19] M. Ghanbarian, D. Afzali, A. Mostafavi, F. Fathirad, Displacement-dispersive liquidliquid microextraction based on solidification of floating organic drop of trace amounts of palladium in water and road dust samples prior to graphite furnace atomic absorption spectrometry determination J.AOACInt. 96 (2013) 880-886. [20] Ş. Saçmacl, Ş. Kartal, S. Dural, Dispersive liquid-liquid microextraction procedure for the determination of palladium by flame atomic absorption spectroscopy, J. Braz. Chem. Soc. 23 (2012) 1033-1040.

ACCEPTED MANUSCRIPT [21] S.Z. Mohammadi, D. Afzali, M.A. Taher, Y.M. Baghelani, Determination of trace amounts of palladium by flame atomic absorption spectrometry after ligandless-dispersive liquid–liquid microextraction, Microchim. Acta 168 (2010) 123-128.

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[22] S. Dadfarnia, A.M.Haji Shabani, M. Amirkavei, Ultrasound-assisted emulsification-

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solidified floating organic drop microextraction combined with flow injection--flame atomic absorption spectrometry for the determination of palladium in water samples, Turk. J.

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Chem.37 (2013) 746-755.

[23] M. Soylak, M. Tuzen, Coprecipitation of gold (III), palladium (II) and lead (II) for their flame atomic absorption spectrometric determinations, J. Hazard. Mater. 152 (2008) 656-661.

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[24] X. Wu, P. Liu, Q. Pu, Q. Sun, Z. Su, Preparation of dendrimer-like polyamidoamine immobilized silica gel and its application to online preconcentration and separation palladium

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prior to FAAS determination, Talanta 62 (2004) 918-923. [25] I. Gaubeur, M.A. Aguirre, N. Kovachev, M. Hidalgo, A. Canals, Dispersive liquid– liquid microextraction combined with laser-induced breakdown spectrometry and inductively

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coupled plasma optical emission spectrometry to elemental analysis, Microchem. J.121

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(2015) 219–226.

[26] L. Tavakoli, Y. Yamini, H. Ebrahimzadeh, A. Nezhadali, S. Shariati, F.

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Nourmohammadian, Development of cloud point extraction for simultaneous extraction and determination of gold and palladium using ICP-OES, J. Hazard. Mater. 152 (2008) 737-743. [27] J. Fang, L.-W. Liu, X.-P. Yan, Minimization of mass interferences in quadrupole inductively coupled plasma mass spectrometric (ICP-MS) determination of palladium using a

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flow injection on-line displacement solid-phase extraction protocol, Spectrochim. Acta, Part B 61 (2006) 864-869.

[28] B.A. Leśniewska, B. Godlewska-Żyłkiewicz, A. Ruszczyńska, E. Bulska, A. Hulanicki, Elimination of interferences in determination of platinum and palladium in environmental samples by inductively coupled plasma mass spectrometry, Anal. Chim. Acta 564 (2006) 236-242. [29] X. Dai, C. Koeberl, H. Fröschl, Determination of platinum group elements in impact breccias using neutron activation analysis and ultrasonic nebulization inductively coupled plasma mass spectrometry after anion exchange preconcentration, Anal. Chim. Acta 436 (2001) 79-85. [30] M. Arab Chamjangali, G. Bagherian, G. Azizi, Simultaneous determination of cobalt, nickel and palladium in micellar media using partial least square regression and direct orthogonal signal correction, Spectrochim. Acta, Part A 62 (2005) 189-196.

ACCEPTED MANUSCRIPT [31] A. Niazi, A. Azizi, M. Ramezani, Simultaneous spectrophotometric determination of mercury and palladium with Thio-Michler's Ketone using partial least squares regression and orthogonal signal correction, Spectrochim. Acta, Part A 71 (2008) 1172-1177.

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[32] F. Shemirani, B. Majidi, Microextraction technique based on ionic liquid for

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preconcentration and determination of palladium in food additive, sea water, tea and biological samples, Food Chem. Toxicol. 48 (2010) 1455-1460.

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[33] R.R. Kozani, J. Mofid-Nakhaei, M.R. Jamali, Rapid spectrophotometric determination of trace amounts of palladium in water samples after dispersive liquid–liquid microextraction, Environ. Monit. Assess.185 (2013) 6531-6537.

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[34] K. Pyrzyńska, Recent advances in solid-phase extraction of platinum and palladium, Talanta 47 (1998) 841-848.

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[35] B. Godlewska-żyłkiewicz, Preconcentration and separation procedures for the spectrochemical determination of platinum and palladium, Microchim. Acta 147 (2004) 189210.

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[36] E. Guibal, N. Von Offenberg Sweeney, T. Vincent, J. Tobin, Sulfur derivatives of

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chitosan for palladium sorption, React. Funct. Polym. 50 (2002) 149-163. [37] A.N. Anthemidis, D.G. Themelis, J.A. Stratis, Stopped-flow injection liquid–liquid

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extraction spectrophotometric determination of palladium in airborne particulate matter and automobile catalysts, Talanta 54 (2001) 37-43. [38] L. Pan, Y.c. Qin, B. Hu, Z.c. Jiang, Determination of nickel and palladium in environmental samples by low temperature ETV-ICP-OES coupled with liquid-liquid

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extraction with dimethylglyoxime as both extractant and chemical modifier, Chem. Res. Chin. Univ. 23 (2007) 399-403. [39] M. Andreia Mesquita da Silva, V. Lúcia Azzolin Frescura, A. José Curtius, Determination of noble metals in biological samples by electrothermal vaporization inductively coupled plasma mass spectrometry, following cloud point extraction, Spectrochim. Acta, Part B 56 (2001) 1941-1949. [40] D.L.G. Borges, M.A.M.S. da Veiga, V.L.A. Frescura, B. Welz, A.J. Curtius, Cloud-point extraction for the determination of Cd, Pb and Pd in blood by electrothermal atomic absorption spectrometry, using Ir or Ru as permanent modifiers, J. Anal. At. Spectrom. 18 (2003) 501-507. [41] A. Ghiasvand, S. Shadabi, E. Mohagheghzadeh, P. Hashemi, Homogeneous liquid– liquid extraction method for the selective separation and preconcentration of ultra trace molybdenum, Talanta 66 (2005) 912-916.

ACCEPTED MANUSCRIPT [42] S. Igarashi, N. Ide, Y. Takagai, High-performance liquid chromatographic– spectrophotometric determination of copper (II) and palladium (II) with 5, 10, 15, 20-tetrakis (4-pyridyl) porphine following homogeneous liquid–liquid extraction in the water–acetic

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acid–chloroform ternary solvent system, Anal. Chim. Acta 424 (2000) 263-269.

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[43] M.A. Jeannot, F.F. Cantwell, Mass transfer characteristics of solvent extraction into a single drop at the tip of a syringe needle, Anal. Chem. 69 (1997) 235-239.

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[44] F. Ahmadi, Y. Assadi, S. Hosseini, M. Rezaee, Determination of organophosphorus pesticides in water samples by single drop microextraction and gas chromatography-flame photometric detector, J. Chromatogr. A 1101 (2006) 307-312.

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[45] C.L. Arthur, J. Pawliszyn, Solid phase microextraction with thermal desorption using fused silica optical fibers, Anal. Chem. 62 (1990) 2145-2148.

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[46] M. Rezaee, Y. Assadi, M.-R. Milani Hosseini, E. Aghaee, F. Ahmadi, S. Berijani, Determination of organic compounds in water using dispersive liquid–liquid microextraction, J. Chromatogr. A 1116 (2006) 1-9.

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[47] S. Berijani, Y. Assadi, M. Anbia, M.-R. Milani Hosseini, E. Aghaee, Dispersive liquid–

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liquid microextraction combined with gas chromatography-flame photometric detection: Very simple, rapid and sensitive method for the determination of organophosphorus

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pesticides in water, J. Chromatogr. A 1123 (2006) 1-9. [48] M.A. Farajzadeh, M. Bahram, J.Å. Jönsson, Dispersive liquid–liquid microextraction followed by high-performance liquid chromatography-diode array detection as an efficient

79.

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and sensitive technique for determination of antioxidants, Anal. Chim. Acta 591 (2007) 69-

[49] J.S. Chiang, S.D. Huang, Simultaneous derivatization and extraction of anilines in waste water with dispersive liquid–liquid microextraction followed by gas chromatography–mass spectrometric detection, Talanta 75 (2008) 70-75. [50] P. Liang, J. Xu, Q. Li, Application of dispersive liquid–liquid microextraction and highperformance liquid chromatography for the determination of three phthalate esters in water samples, Anal. Chim. Acta 609 (2008) 53-58. [51]X. Wen, Q. Yang, Z. Yan, Q. Deng, Determination of cadmium and copper in water and food samples by dispersive liquid–liquid microextraction combined with UV–vis spectrophotometry, Microchem. J. 97 (2011) 249–254. [52] N. Shokoufi, F. Shemirani, Y. Assadi, Fiber optic-linear array detection spectrophotometry in combination with dispersive liquid–liquid microextraction for

ACCEPTED MANUSCRIPT simultaneous preconcentration and determination of palladium and cobalt, Anal. Chim. Acta 597 (2007) 349-356. [53] H. Jiang, Y. Qin, B. Hu, Dispersive liquid phase microextraction (DLPME) combined

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with graphite furnace atomic absorption spectrometry (GFAAS) for determination of trace Co

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and Ni in environmental water and rice samples, Talanta 74 (2008) 1160-1165. [54] M. Talismanova, A. Sidorov, G. Aleksandrov, Y.F. Oprunenko, I. Eremenko, I.

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Moiseev, New dinuclear palladium complex with a Chinese-lantern structure, Russ. chem. bull. 53 (2004) 1507-1510.

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Table 1. Interferences for determination of Pd(II) (0.20 µg mL−1).

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Species

Tolerance limit (Wspecies/WPd)

Cr3+, Cr6+, Mn2+, Li+, Co2+, K+, Na+, NO3-, Cl-, BrO3-, ClO4-, Al3+, Pb2+, Ni2+, Mg2+, Ca2+, Ba2+, NO2-,

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H2PO4-, HPO42-, HCO3-, SO42-, Zn2+, Cd2+, I-, F-, Br-,

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Cu2+ Ag+

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Fe2+, Fe3+

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citrate, SO32-

5000

1000 100 50 2

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Table 2. Determination of palladium(II) in real samples. Found

(µg L-1)

(µg L-1)

Mojen

-

Waterfall Water

Calculated t-

Sample content

(%)

value

(µg g-1)

Not detected

-

-

40.0

39.2 (±1.1)a

98.0

1.3

100.0

101.3 (±1.3)

1.7

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101.0

200.0

198.1 (±1.9)

99.1

1.7

-

Not detected

-

-

40.0

38.9 (±1.2)

97.2

1.6

100.0

102.4 (±1.5)

102.4

2.8

200.0

198.2 (±1.9)

99.1

1.6

-

28.7 (±0.9)

-

-

40.0

67.8 (±1.2)

99.8

1.3

100.0

130.3 (±1.4)

101.6

2.0

200.0

227.1 (±1.7)

99.2

1.6

-

Not detected

-

-

40.0

41.2 (±1.3)

103.0

1.6

100.0

102.4 (±1.6)

102.4

2.6

200.0

197.5 (±1.6)

98.8

2.7

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Shahrood

Recovery

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Water

Soil

Garlic

a)

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Added

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Sample

±Standard deviation (n = 3).

-

-

0.72

-

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Figure captions Fig. 1. Absorption spectra for (a) MBI and (b) Pd-MBI complex solutions. Conditions:

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pH=5.0 (acetate/acetic acid), 5.0 mg L-1 of Pd(II), 3.0 × 10-4 mol L-1 of MBI.

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Fig. 2. Effect of pH on the extraction of Pd(II) by the DLLME method. Conditions: 10 mL of aqueous sample, 0.20 µg mL−1 Pd(II), 6.0×10-5 mol L-1of MBI, 1.38 mL of acetone (dispersive solvent), 120 µL of chloroform (extraction solvent), rate of centrifugation of 5000rpm.

Fig.3. Effect of volume of chloroformon the extraction of Pd(II) by the DLLME method. Conditions: 10.0 mL of sample solution, 0.20 µg mL−1of Pd(II), 6.0×10−5 mol L−1ofMBI,

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pH= 5.0, 1.38 mL of acetone (dispersive solvent).

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1.6

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Fig 4. Effect of volume of acetone on the extraction of Pd(II) by DLLME method. Conditions: 10 mL of aqueous sample, 0.20 µg mL−1 of Pd(II), 6.0×10-5 mol L-1 of MBI, pH=5.0, 150 µL of chloroform (extraction solvent), rate of centrifugation of 5000rpm.

1.2

a

A 0.8 0.4

b

0 250

300

350

400

λ (nm) Fig. 1

450

500

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0.09

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0.08

A

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0.07

0.06

0

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0.05 2

4

6

8

pH

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Fig. 2

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0.11

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0.1 0.09

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A 0.08 0.07

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0.06 0.05

70

90

110

130

150

Chloroform volume (µL) Fig. 3

170

190

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0.09

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A

0.05 0.5

0.7

0.9

1.1

1.3

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0.07

1.5

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Acetone volume (mL)

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Fig. 4

1.7

1.9

2.1

ACCEPTED MANUSCRIPT Highlights 1- In this method, 2-mercaptobenzimidazole(MBI) was used as a chelating agent, which formed a stable and hydrophobic complex with palladium(II) ions.

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2- The reaction between Pd(II) and MBI is very fast.

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3- 2-mercaptobenzimidazole(MBI) is a selective reagent for Pd(II), thus the DLLME has good selectivity. 4- The developed method is a selective, rapid, sensitive, and an environmentally friendly

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method for ultra- trace analysis of Pd.