Separation and pre-concentration of palladium(II)

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Separation and pre-concentration of palladium(II) from environmental and industrial samples by formation of a derivative of 1,2,4-triazole complex on Amberlite XAD–2010 resin a

b

c

Huseyin Serencam , Volkan Numan Bulut , Mehmet Tufekci , d

c

c

Ali Gundogdu , Celal Duran , Sibel Hamza & Mustafa Soylak

e

a

Faculty of Engineering, Department of Food Engineering, Bayburt University, 69000 Bayburt, Turkey b

Maçka Vocational School, Karadeniz Technical University, 61750 Maçka/Trabzon, Turkey c

Department of Chemistry, Faculty of Sciences, Karadeniz Technical University, 61080 Trabzon, Turkey d

Faculty of Engineering, Department of Food Engineering, Gumushane University, 29100 Gumushane, Turkey e

Department of Chemistry, Faculty of Sciences, Erciyes University, 38039 Kayseri, Turkey Version of record first published: 13 Feb 2013.

To cite this article: Huseyin Serencam , Volkan Numan Bulut , Mehmet Tufekci , Ali Gundogdu , Celal Duran , Sibel Hamza & Mustafa Soylak (2013): Separation and pre-concentration of palladium(II) from environmental and industrial samples by formation of a derivative of 1,2,4triazole complex on Amberlite XAD–2010 resin, International Journal of Environmental Analytical Chemistry, DOI:10.1080/03067319.2012.755676 To link to this article: http://dx.doi.org/10.1080/03067319.2012.755676

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Intern. J. Environ. Anal. Chem., 2013 http://dx.doi.org/10.1080/03067319.2012.755676

Separation and pre-concentration of palladium(II) from environmental and industrial samples by formation of a derivative of 1,2,4-triazole complex on Amberlite XAD–2010 resin


Huseyin Serencama, Volkan Numan Bulutb*, Mehmet Tufekcic, Ali Gundogdud, Celal Duranc, Sibel Hamzac and Mustafa Soylake a

Faculty of Engineering, Department of Food Engineering, Bayburt University, 69000 Bayburt, Turkey; bMaçka Vocational School, Karadeniz Technical University, 61750 Maçka/Trabzon, Turkey; cDepartment of Chemistry, Faculty of Sciences, Karadeniz Technical University, 61080 Trabzon, Turkey; dFaculty of Engineering, Department of Food Engineering, Gumushane University, 29100 Gumushane, Turkey; eDepartment of Chemistry, Faculty of Sciences, Erciyes University, 38039 Kayseri, Turkey (Received 18 May 2012; final version received 1 December 2012) A simple separation/pre-concentration method was developed for extraction of Pd(II) in various environmental samples, based on its adsorption of 4–phenyl–5– {[(4–phenyl–5–pyridin–4–yl–4H–1,2,4–triazole–3–yl)thio]methyl}–4H–1,2,4–triazole–3–thyol (PPTTMET) complex on Amberlite XAD–2010 resin in a mini column. The ligand has high affinity for Pd(II) among many other metals that are taken into consideration. The flame atomic absorption spectrometry is employed to determine the concentration of Pd(II). The optimum working conditions which were determined are as follows: 0.05 mol L1 HNO3 as working medium, 1.0 mol L1 HCI in acetone as elution solvent, 0.75 mg of PPTTMET amount and 750 mL of sample volume. The system was independent from the flow rates between 3.1 and 23.1 mL min1. The Pd(II) adsorption capacity of Amberlite XAD–2010 resin was found to be 12.8 mg g1 and the enrichment factor was calculated as 375. The method was successfully applied for the determination of Pd(II) in motorway dust samples, anodic sludge, gold ore, industrial electronic waste materials and various water samples. Keywords: solid phase extraction; 4–phenly–5–{[(4–phenly–5–pyridyn–4–yl–4H– 1,2,4–triazole–3–yl)thio]methyl}–4H–1,2,4–triazole–3–thyol; palladium(II); flame atomic absorption spectrometry

1. Introduction Palladium (Pd), a naturally rare and lustrous silvery-white appearance metal, is one of the platinum group metals (PGM). PGMs (Pt, Pd, Rh, Ir, Ru, and Os) are extremely rare when compared with the other metals. This situation is not just a result of low occurrence of palladium in the nature but also the difficulties involved in the processes of extracting and refining [1,2]. Among others, the catalytic converters used in the vehicles to reduce the harmful emission are the most important factor that make Pd a highly important material. Pd that

*Corresponding author. Email: [email protected] 2013 Taylor & Francis


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has a largest and fastest growing demand in autocatalyst and electronics industry does not have any biological role. However, almost all Pd compounds are considered to be highly toxic and carcinogenic substances. The World Health Organization considers that Pd exposures exhibit many possible risks to human health and environment [3]. Pollution caused by palladium, either environmental or industrial, has been investigated by many researchers as opposed to the other heavy metals, such as mercury, plutonium, lead, cadmium, etc. It has been shown that long-term exposure to Pd may have an adverse effect on human health. Even small amounts of Pd can cause allergic reaction in sensitive individuals, and it makes the health concern a sensitization risk of Pd [4]. The monitoring of Pd and other heavy metals in environmental samples is an important issue for evaluating the risks on the human health and the ecosystem that may occur in the future [5]. The quantitative methods for determining Pd as well as the other pollutants in various samples, such as catalysts, industrial, environmental, geophysical, and biological, have become an attractive research field [6]. Several sensitive instrumental methods, including atomic spectrometry, have been used in order to determine Pd and other heavy metals in environmental samples. Accuracy of all these methods is disturbed by the matrix of the samples. It is also a problem if the levels of analytes are lower than the limit of detection of instruments. Owing to these problems, a separation–pre-concentration step for solutions is often necessary before determining the levels of analytes. The techniques for separation–pre-concentration of trace metals including solvent extraction [7], co–precipitation [8], electrochemical deposition [9], cloud point extraction [10], ion-exchange and membrane filtration [11,12] are commonly used. Solid phase extraction is the most preferable method as compared to the others for preconcentration and separation of trace metal ions. The advantages of solid phase extraction, are its, high enrichment factor, easy to apply and easy to regenerate for multiple applications, reduced consumption and exposure to solvent, and disposal costs, shorter extraction time [13], thereby providing linear results for wide range of concentration of analytes and good reproducibility in the sorption characteristics [14,15]. Various sorbents, such as Dowex Optipore V-493 [16], polymeric supports [17], Diaion HP–2MG [18], naphthalene [19], octadecyl bonded silica membrane disk [20], Dowex M 4195 [21], etc. have been successfully used by various researchers for pre-concentration and separation of traces metal ions up until now. In the solid phase extraction studies for trace metal ions in environmental samples, the sorbent family of Amberlite XAD resin plays an important role. This family can be divided into two major groups: (i) polystyrene-divinyl benzene based resins and (ii) polyacrylic acid ester based resins. The specific surface area, polarity and specific pore volume of Amberlite XAD resin are attributed to its high affinity to absorbable compounds. Amberlite XAD–2010, used in this study, is a polystyrene-divinyl benzene based resin with a 660 m2 g1 surface area, 280 A˚ pore diameter, 20–60 bead mesh size and 1.80 mL g1 pore volume, and recently, it has been used successfully in a few studies [22,23]. In order to retain the metals on a non-polar resin such as Amberlite XAD–2010, generally they need to be complexed with suitable organic ligands. Various complexing agents, such as morpholine-4-carbodithioate [24], diethyldithiocarbamate [25], 1-nitroso-2naphthol [26], etc. have been widely used for this purpose. The ligand used in this study, 4–phenyl–5–{[(4–phenyl–5–pyridin–4–yl–4H–1,2,4– triazole–3–yl)thio]methyl}–4H–1,2,4–triazole–3–thyol (PPTTMET), is a 1,2,4-triazole derivative (Figure 1). High Pd(II) affinity of PPTTMET compared to all other metals is examined in this study.

International Journal of Environmental Analytical Chemistry

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Figure 1. Structure of 4–phenyl–5–{[(4–phenyl–5–pyridin–4–yl–4H–1,2,4–triazole–3–yl)thio] methyl –4H–1,2,4–triazole–3–thyol (PPTTMET).

It’s been observed in time that 1,2,4–triazole and its derivatives are highly active compounds with a wide spectrum of biological properties. Their properties of being antihypertensive, anticonvulsant, antimicrobial, analgesic, antiviral, antioxidant, antiinflammatory, antitumor and, anti-HIV, pesticidal, insecticidal, herbicidal and fungicidal activity are well-known. In addition to these properties, 1,2,4–triazole derivatives have the ability of complex forming with many metals. Triazoles are an important class of ligands for magnetochemical applications as they have ability to bind metal ions to form new compounds. More interestingly, in some molecular based memory devices and optical sensors, some complexes containing substituted 1,2,4–triazole ligands are used. Lately, some studies using the triazole derivatives for separation and pre-concentration of heavy metals have been reported [27–29]. The main objective of the present study is to develop a rapid and sensitive separation– pre-concentration method based on the solid phase extraction for the accurate determination of Pd(II) levels in environmental and industrial samples by flame atomic absorption spectrometry (FAAS). Before applying the method to the real samples, the optimum analytical conditions for the quantitative recoveries of Pd(II), including pH of the solution, sample volume, elution solvent, sample and eluent flow rates, effects of interfering ions and the Pd(II)–PPTTMET complex capacity of Amberlite XAD–2010 resin were investigated and then optimized.

2. Experimental 2.1 Instruments A Unicam AA–929 flame atomic absorption spectrometer equipped with a single element hollow-cathode lamp, 5.0 cm of an air–acetylene burner head and a deuterium background correction system was used for the determination of Pd(II) concentration in the aqueous solutions. The selected wavelength for Pd is 247.6 nm. Absorbance measurements were made using a Dr. Lange Cadas 200 UV–Vis Spectrophotometer with 1.0-cm quartz cells. The instrumental parameters are chosen as recommended by the manufacturer. A digital desktop pH meter (Hanna Instruments Model pH 211) with glass electrodes was used for all pH adjustments. Milestone Ethos D closed vessel microwave system (maximum pressure 1450 psi; maximum temperature 300 C) was operated for obtaining the clear solutions by digesting the solid samples.

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2.2 Reagents and solutions An analytical grade of Merck (Darmstadt, Germany) or Fluka (Buchs, Switzerland) chemicals were used in this study. 1% nitric acid was used to dissolve an appropriate amount nitrate salt of analyte to prepare a stock standard solution of Pd(II), 1000 mg L1. The stock Pd(II) ion solution was diluted daily to prepare reference and working solutions. Amberlite XAD–2010 resin, used as an adsorbent in this study, was supplied by Sigma Chem. A certified reference material, CRM–SA–C Sandy Soil C, purchased from HighPurity Standards, Inc., was used to validate the method. Distilled/deionized water was used for all experiments. 1:10 HNO3–H2O solution was used to soak all glassware and plastics used in the experiments for one day and then cleaned with distilled/deionized water. For adjusting the pH values of the solutions, the following buffer solutions were prepared: Buffer of pH 2 was prepared by mixing an appropriate volume of 1 mol L1 sodium sulfate and 1 mol L1 sodium hydrogen sulfate solutions. In order to maintain the pH between 4 and 6, different amounts of 1 mol L1 sodium acetate and 1 mol L1 acetic acid were used to prepare acetate buffers. In order to produce solutions with a pH of 8–10 ammonium chloride buffer solutions (0.1 mol L1) were prepared by mixing an appropriate amount of ammonia to ammonium chloride solutions. In this study, PPTTMET was synthesized according to a previously proposed procedure [30]: 0.4 g of sodium hydroxide was added to a solution of 4.61 g of N-phenyl-2{[(4-phenyl-5-pyridin-4-yl-4H-1,2,4-triazole-3-yl)thio]acetyl}hydrazinecarbothioamide, which was obtained by the reaction of 2-[(4-phenyl-5-pyridin-4-yl-4H-1,2,4-triazol-3yl)thio]acetohydrazide [31] with phenylisothiocyanate, was refluxed in ethanol for 3 h. The resulting solution was cooled and acidified to pH 7 with HCl. The precipitate formed was filtered, washed with water and recrystallized from dimethyl sulfoxide/water (1 : 1) to afford the desired product. Yield 92.72%, m.p. 200–201 C. IR (KBr, v, cm1): 1608 and 1438(C¼N), 1497 (2C¼N), 2743 (SH); 1H NMR (DMSO–d6, /ppm): 4.21 (s, S–CH2), 7.25–7.32 (6H, m, ArH), 7.51–7.61 (6H, m, ArH), 8.56 (2H, brs, ArH); 13C NMR (DMSO–d6, /ppm): 27.18 (CH2), ArC: [121.44 (2CH), 127.34 (2CH), 128.15 (2CH), 129.27 (2CH), 129.54 (CH), 130.06 (2CH), 130.43 (CH), 133.00 (2C), 133.54 (C), 150.05 (2CH),], 150.03 (triazole C–3), 168.05 (triazole C–5). The necessary precautions were taken when PPTTMET was handled in the experiments because there was no safety data available for this compound in the literature.

2.3 Preparation of the column A glass mini-column (manufactured by Ildam, Ankara, Turkey), having a 13 cm length– 1.0 cm diameter, porous disk and a stopcock, was used for pre-concentrating Pd(II). 250 mg of Amberlite XAD–2010 resin beads was placed into the column. Before using the resin, it was grounded, sieved to 150–200 mm, to obtain a better adsorption process by increasing the surface area of the resin, and then washed successively with 1 mol L1 NaOH, water, 1 mol L1 HNO3, water, acetone and water [22,32]. The Amberlite XAD– 2010 resin used in the column was washed thoroughly with distilled/deionized water and then with the related buffer solution after every experiment, and then stored in distilled/ deionized water for the next applications [22,25].


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2.4 Sampling and pre-treatments Polyethylene bottles (5 L) were used for sampling the surface water from the Solakli River, Trabzon, Turkey and sea water from Trabzon Port. The bottles were pre-cleaned with detergent first, and then rinsed with distilled–deionized water, which was followed a 1 mol L1 HNO3 bath, and then were rinsed again with distilled–deionized water. After sampling, high-purity HNO3 was added to samples to keep the pH at nearly 2. The water samples were filtered immediately after being collected using a nitro-cellulose membrane with a pore size of 0.45 mm (Millipore Corp.), and stored at 4 C until they were used. The developed procedure was also applied to various solid samples; anodic slime, gold ore, motorway dust, soil and industrial electronic waste materials. The method was finally applied to a certified reference material CRM-SA-C Sandy Soil C. The solid samples were digested with a closed microwave digestion system as follows: 0.5 g of anodic slime (HES/ Kayseri, Turkey), gold ore (Akoluk/Ordu, Turkey), motorway dust (Trabzon–Samsun motorway), soil (Çaykara/Trabzon, Turkey), CRM-SA-C Sandy Soil C samples and 0.25 g of material composed of industrial electronic waste were weighed into vessels made of teflon separately with a sensitivity of 0.1 mg. 4.5 mL of HCl, 1.5 mL of HNO3, 2.0 mL H2O2 and 1.0 mL HF were added into the vessels. Digestion of the solid samples by microwave radiation was performed in four steps. In the first step, the samples were exposed to 250 W radiations for 6 min. It is followed by a 400 W radiation for 6 min. In the third step, radiation power 650 W for 6 min. The last step is 6 min radiation at 250 W level. During all these microwave radiations the pressure is kept at 45 bars, and the ventilation was 3 min. At the end of microwave digestion, the total volume of the sample was 250 mL including distilled/deionized water and then the method was applied.

2.5 General procedure 0.1% (w/v) solution of complexing agent (PPTTMET) was prepared in a mixture of ethanol-water (in a ratio of 4 : 1). Then, 0.75 mL of PPTTMET solution was added into a 50 mL of 0.05 mol L1 HNO3 solution containing 5.0 mg Pd(II). The solution was stirred for 2 min and left to rest for 10 min in order to make sure that formation of metalPPTTMET complex was completed. After this process, a column packed with Amberlite XAD–2010 was used to pass through the solution. The Pd(II)–PPTTMET complex retained in the resin column was stripped with 7.5 mL of 1.0 mol L1 HCl in acetone. The acetone phase in the eluent solution was evaporated to near dryness on a hot plate at 40 C in 5 min. The residue was reconstituted in 2.0 mL distilled/deionized water. Under these conditions, separation and preconcentration stage was completed between 25–30 min. Finally, the solution was analyzed by FAAS for Pd(II) level.

3. Results and discussion 3.1 Complexation and spectrophotometric properties The absorption spectra of Pd(II)–PPTTMET complex and free ligand PPTTMET were recorded, and the complex formation was demonstrated. The maximum absorption was observed at 390 nm and the free ligand was obtained at 290 nm (Figure 2). Control of complex formation between Pd(II) and PPTTMET, and their stoichiometry (1 : 1) were carried out according to Job’s method of continuous variation. It was also examined whether the ligand forms complexes with other individual metals including Cr(III), Cr(VI),


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Figure 2. Absorption spectrum of Pd(II)–PPTTMET complex.

Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Mo(VI), Ag(I), Cd(II), Au(III), Pt(IV), Pd(II), Hg(I), Hg(II), Al(III), Pb(II), Sn(II), Sb(III), Bi(III), As(III), Se(IV), Li(I), Na(I), K(I), Mg(II) and Ca(II). However, no color and absorption peaks were observed for the possible complexes of PPTTMET with these metals, so it was clearly demonstrated the affinity of PPTTMET for Pd(II) compared to the other metal ions. The experiments were also conducted by using 0.75 mL of PPTTMET solutions (0.1% (w/v)), which were added into 50 mL HNO3 solutions (HNO3 concentrations: 0.025, 0.05 and 0.1 mol L1) containing 5.0 mg of Pd(II) and treated with the above mixture of metal ions. After the column was eluted with 7.5 mL of 1.0 mol L1 HCl in acetone, the concentration of metal ions in the eluate were determined by FAAS. Because absolute quantities are not determined for other metal ions by this approach, it was proved that the ligand was suitable for only preconcentration of Pd(II) ions (Table 1) [33,34]. 3.2 Effects of pH and HNO3 concentration on the recovery of the analyte In Section 2.2., relevant buffer solutions were used to investigate the effect of pH on the recovery of Pd(II) ions in the pH range from 1.0 to 10.0. It is well known that the formation of complexes that is subsequently followed by extraction is heavily affected by the pH value of the sample solution. The pH value of the solution also affects ionization state of functional groups of the ligands. As it is seen from Figure 3, the highest Pd(II) recoveries was obtained at the lower pH values. Therefore, it is said that the more stable Pd(II)–PPTTMET complex occurs at higher acidic media. At pH greater than 2.0, the quantitative recoveries (495%) of Pd(II) ions cannot be achieved owing to hydrolysis at higher pH values. Palladium tends to form anionic inorganic complexes in acidic medium (such as PdðNO3 Þ 3 in HNO3) [35]. Therefore, strong interactions occur between the anionic species of Pd(II) and PPTTMET. Because more stable complexes of Pd(II) occurs in lower pH values, it is important to investigate the effects of acidic medium concentration on the Pd(II) recovery in terms of separation and pre-concentration. Acidic solutions are also an advantage for separation and pre–concentration of Pd(II) ions because strong acids are usually effective on decomposing many materials, including Pd(II) [9].


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Table 1. Effect of HNO3 concentration on the recovery of different ions (N: 3, RSD 5 6.0%).


Concentration of HNO3 (mol L1) Tested Ions

0.025

0.05

0.1

Cr(III) Cr(VI) Mn(II) Fe(III) Co(II) Ni(II) Cu(II) Zn(II) Mo(VI) Ag(I) Cd(II) Au(III) Pt(IV) Pd(II)* Hg(I) Hg(II) Al(III) Pb(II) Sn(II) Sb(III) Bi(III) As(III) Se(IV) Li(I) Na(I) K(I) Mg(II) Ca(II)

2.0 2.3 5.1 1.7 3.0 1.7 6.7 4.2 1.2 2.3 4.4 15.2 7.2 93.3 2.4 3.5 4.6 3.8 3.1 2.9 2.1 1.9 1.7 0.9 0.3 2.2 2.4 1.1

2.2 1.8 5.4 2.5 3.4 2.3 6.9 3.6 0.8 2.7 3.9 17.0 7.8 97.4 2.9 3.6 4.7 3.3 3.4 2.7 2.3 1.1 1.6 0.2 0.4 2.9 2.3 1.5

2.8 1.6 5.9 2.9 2.8 1.1 6.1 3.3 1.4 2.1 4.5 19.3 6.9 98.1 3.2 3.1 4.3 2.7 3.8 2.5 2.6 0.8 1.2 0.5 0.9 2.6 2.6 1.3

*Figures in bold show the metal with the highest recovery value among the studied metals.

The influence of nitric acid concentration on the retention of Pd(II)–PPTTMET complex on Amberlite XAD–2010 resin was investigated in the HNO3 concentration range of 0.01 to 1.0 mol L1. The quantitative recoveries (495%) for Pd(II) ions were obtained in the presence of HNO3 in the concentration range from 0.05 to 1.0 mol L1. Therefore, subsequent experiments were carried out with 0.05 mol L1 HNO3 medium.

3.3 Effect of quantity of complexing agent Separation and quantitative pre-concentration of Pd(II) is affected most from PPTTMET quantity among other chemical variables. Therefore, the influences of quantities of PPTTMET as a chelating agent on the solid phase extraction of Pd(II) were investigated in the quantity range from 0 to 2.0 mg. The recovery of Pd(II) was 40.2%, when PPTTMET was not added to the solution. The recovery values increased with the addition of PPTTMET. These results show that for quantitative recovery of Pd(II) ions, PPTTMET


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Figure 3. Effect of pH on the recovery of Pd(II) ions (N ¼ 3).

is necessary. The quantitative recoveries (495%) for Pd(II) ions were obtained after 0.75 mg (0.75 mL of 0.1% (w/v)) of PPTTMET. In all working range of PPTTMET above this point the recoveries were quantitative. 0.75 mg of PPTTMET was added to the solution for all subsequent works.

3.4 Effect of eluent type, concentration and volume In order to identify the best eluent for the adsorbed Pd(II)–PPTTMET complex on Amberlite XAD–2010, a variety of acids and organic solvents were tested. The results were summarized in Table 2. The acids with acetone resulted in higher recovery efficiency compared to the acids in aqueous and alcoholic solutions. Therefore, the solutions with HCl and HNO3 in acetone provided the highest recoveries of Pd(II). The use of acetone with hydrochloric acid is based on the assumption that acetone determines a change of the dielectric constant of the environment which leads to the chlorocomplexes of palladium such as [PdCl]þ, PdCl2, [PdCl3] and [PdCl4]2 desorption [36]. Finally, 1.0 mol L1 HCl in acetone was specified as the best eluent for stripping of Pd(II) complexes from the resin column and was used for the optimization of the other parameters. It has been concluded that the quantitative recoveries were obtained after 5.0 mL of the eluent, after having investigated the effects of 1.0 mol L1 M HCl solutions in acetone with volumes 2.5, 5.0, 7.5, 10.0 and 15.0 mL. The optimum eluent volume is specified as 7.5 mL for the subsequent studies.

3.5 Effect of sample volume As the concentration of Pd in real samples was very low, optimization of sample volume is one of the most important parameters to reach high pre-concentration factor for the analysis of a real sample using solid phase extraction. Therefore, the effect of sample


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Table 2. The influences of eluent type on the recovery (Sample volume: 50 mL, N ¼ 3). Type of eluent


1

1 mol L HCl 1 mol L1 HCl in ethanol 1 mol L1 HNO3 1 mol L1 HNO3 in ethanol 1 mol L1 H2SO4 1 mol L1 H2SO4 in ethanol 1 mol L1 HNO3 in ethanol 1 mol L1 H2SO4 in ethanol 1 mol L1 KI 1 mol L1 KSCN 1 mol L1 KCN 1 mol L1 (NH2)2CS (CH3)2CO C2H5OH 3 mol L1 HCl1 mol L1 (NH2)2CS 0.5 mol L1 HCl in acetone 1 mol L1 HCl in acetone 1.5 mol L1 HCl in acetone

% Recovery of Pd(II) 8.9 0.5 83.1 3.9 5.2 0.3 66.5 2.7 2.8 0.2 80.2 4.8 86.6 5.2 81.7 4.9 4.9 0.3 14.5 0.8 26.0 1.5 24.8 1.5 41.7 2.5 14.8 0.9 25.3 1.5 90.4 5.1 97.2 6.0 97.2 5.4

volume on the recoveries of the analyte were investigated by using different volumes (50, 250, 500, 750, 1000 and 1500 mL) of model solutions containing the 5.0 mg fixed amount of Pd(II) which were passed through a column containing Amberlite XAD–8 resin under optimal conditions. The recoveries were found to be stable until volume of 750 mL. Hence, 750 mL was chosen as the largest sample volume to work quantitatively. The preconcentration factor is calculated by the ratio of the highest sample volume and the lowest final volume, and it was found as 375 for Pd(II) when the final volume was 2.0 mL.

3.6 Effect of flow rate of sample and eluent solution The flow rate of the model solutions through the column is another factor affecting the duration of the contact of the solution with the resin, and therefore provides information about the adsorption rate of the complexes on the resin. The model solutions of 50 mL were passed through the column with the flow rates varying between 3.1 mL min1 and 23.1 mL min1 by using a water jet aspirator, and it was observed that the recovery was almost always quantitative and not changed significantly. The flow rates of eluent solution were investigated in the range of 0.5 to 30 mL min1. It was also observed that the quantitative recovery was not changed significantly. The results indicated that the recovery did not change significantly at the investigated flow rates.

3.7 Adsorption capacity of the resin For determination of the resin capacity, defined as the amount of analyte adsorbed by 1 g of resin, Langmuir isotherms were plotted. Langmuir adsorption model is one of the

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most well-known adsorption isotherms, and described in linear mode by the equation below [37]


Ce Ce 1 ¼ þ qe qmax aL qmax

ð1Þ

where qe is the amount of metal adsorbed per unit weight of the resin (mg g1) at equilibrium, Ce the final concentration in the solution (mg L1), qmax the maximum adsorption in mono-layered adsorption systems (mg g1), and aL the adsorption equilibrium constant related to adsorption energy (Lmg1). A plot of Ce/qe versus Ce exhibits a linear relationship, and Langmuir constants qmax and aL can be calculated from the slope and intercept of the plot. In order to determine the resin capacity (Amberlite XAD-2010) for Pd(II) ions in this study, PPTTMET complexes of Pd(II), of which total amounts varied in the range of 500 to 10,000 mg, were loaded onto the column filled with 250 mg Amberlite XAD-2010, and the Pd(II) recoveries were investigated. The values of Ce and qe, mentioned above were calculated and the adsorption capacity (qmax) of the Amberlite XAD-2010 resin for Pd(II), obtained from the slope of plot between Ce/qe against Ce, was evaluated as 12.8 mg g1.

3.8 Effect of interfering foreign ions The effects of some foreign ions were examined on the quantitative recovery of Pd(II) ions from aqueous solutions in order to assess the possible analytical applications of the separation and pre-concentration procedure. To this end, the working solutions containing fixed amount (5.0 mg) of Pd(II) together with either individual matrix ions or mixed matrix ions given in Table 3, were prepared and the separation and pre-concentration procedure was applied under optimal conditions. The results obtained in this investigation are summarized in Table 3. The tolerable levels of some heavy metal cations and common anions are suitable for the separation and pre-concentration of Pd(II) from very complex matrices. The effects of interferences from various transition metal ions, having possibility of a complex forming with PPTTMET, such as Mo(VI), V(V), Sn(IV), Fe(III), Cd(II), Zn(II), Cr(III), Pb(II), Cu(II) etc. were examined over the separation and pre-concentration of Pd(II). It is observed that corresponding metal ions did not interfere significantly as no complex was observed for these metal complexes. It is due to instability of metal complexes [38]. Different concentrations of alkaline and earth alkaline elements, Na(I), K(I), Ca(II) 2 and Mg(II), and some anions, NO 3 , Cl and SO4 , were added individually to 100 mL of solution containing 5.0 mg of Pd(II). Large amounts of these ions are found in various environmental samples. From Table 3 tolerance limits, defined as the foreign ion concentration causing an error smaller than 5% in the determination of the analyte, of these ions are much higher than other ions.

3.9 Analytical figure of merit The precision of the method has been determined by applying the method to 50 mL of 10 model solution containing 5.0 mg of Pd(II) on the optimal conditions. Accordingly, the


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Table 3. Tolerance limits of some common interfering anions and cations on the separation and preconcentration of Pd(II) (N:3).


Ions Hg2þ Sb3þ Se4þ Mo6þ Cr3þ Cd2þ Bi3þ Pb2þ Co2þ As3þ Ni2þ V5þ Liþ Be2þ Sn2þ Fe3þ Cu2þ Mn2þ Zn2þ Al3þ Ca2þ Mg2þ Naþ Kþ NO 3 Cl 2 SO4

Added salts

Tolerance limits (mg L1)

Hg(NO3)2 H2O Sb2O3 SeO2 (NH4)6Mo7O24 4H2O Cr(NO3)3 Cd(NO3)2 4H2O BiO(NO3) Pb(NO3)2 Co(NO3)2 6H2O As2O3 Ni(NO3)2 6H2O V2O5 LiNO3 The solution of metallic Be in HNO3 SnCl2 2H2O FeCl3 6H2O Cu(NO3)2 3H2O Mn(NO3)2 4H2O Zn(NO3)2 6H2O Al(NO3)3 9H2O Ca(NO3)2 4H2O Mg(NO3)2 7H2O NaCl KNO3 NaNO3 NaCl Na2SO4

100 150 125 150 100 125 50 100 100 100 150 50 150 100 75 1000 1000 500 500 2500 2000 1000 10,000 3000 5000 25,000 1000

precision of the method was found to be 96.1 5.9% at the 95% confidence level, and the relative standard deviation (RSD) was 6.2%. In the SPE method combined with Pd(II)–PPTTMET/FAAS, the analytical and instrument limit of detection (LOD) for Pd(II) were calculated as three times as the standard deviation of 10 replicate measurements of blank sample with and without the pre-concentration step [18,39]. From the blank measurements by FAAS, the analytical LOD was found 0.6 mg L1 by dividing the instrumental LOD to the pre-concentration factor (375). The accuracy of a method is the closeness of the measured value to the true value for the sample. The accuracy of the developed method was determined in two ways: (i) Spiked/ recovery testing, and (ii) the analysis of the certified reference materials. After different solid–liquid samples were spiked analytical recovery was assessed for two concentration levels. For this purpose, 0.5 g of solid samples were digested according to Section 2.4 with microwave digestion system. At the end of microwave digestion, final volume of the samples was completed to 50 mL. Digested solid samples and liquid samples solutions were spiked with 0–10 mg of Pd(II) ion and then recommended procedure mentioned above in section 2.5 was applied to these solutions. As can be seen Table 4, good recoveries were reached for Pd(II). The method was validated by

12

H. Serencam et al.

Table 4. Spiked/recovery test for Pd(II) to the liquid and solid samples for the accuracy of the method (N: 3, Sample volume: 50 mL (liquid samples), sample quantity: 0.5 g (solid samples), final vol.: 2 mL) (x U*).


Samples

Added (mg)

Found (mg)

Recovery (%)

Solakli Stream (Çaykara/Trabzon, Turkey)

– 5 10

– 4.8 0.7 9.8 1.5

– 96 4.1 98 4.7

Sea water (Trabzon port)

– 5 10

– 5.1 0.8 9.5 1.4

– 102 4.2 95 5.0

Soil (Trabzon, Turkey)

– 5 10

– 4.6 0.7 9.8 1.5

– 92 4.3 98 4.0

Gold ore (Akoluk/Ordu, Turkey)

– 5 10

2.1 0.3 6.7 1.0 12.0 1.8

– 94 3.7 99 5.2

Motorway dust (Trabzon, Turkey)

– 5 10

– 4.7 0.7 10.1 1.5

– 94 4.6 101 4.6

Anodic sludge (Hes Cable/Kayseri, Turkey)

– 5 10

9.6 1.4 14.7 2.2 19.1 2.9

– 101 5.1 97 5.4

Electronic waste (Trabzon, Turkey)**

– 5 10

10.1 1.5 14.8 2.3 20.2 3.1

– 98 5.8 101 5.4

pffiffiffiffi *U ¼ Confidence interval, U ¼ ts= N, t ¼ 4.30 (95% confidence level), N ¼ 3, x ¼ mean value, **Sample quantity: 0.25 g.

Table 5. Student’s t-test for statistical evaluation and analysis of certified reference material for the accuracy of the method (x U). Data Element Pd(II)

s

XR

x

Recovery (%)

pffiffiffiffi t ¼ ðX XR Þ N=s

Comparison

0.2

4**

4.1**

103

0.80

0.8 5 4.30*

*t ¼ 4.30 (95% confidence level); N ¼ 3; s ¼ standard deviation X ¼ mean value; XR ¼ Reference value (Sandy Soil C (CRM–SA C) Standard Reference Material); Sample quantity: 0.5 g. **Pd(II) Concentration (mg g1).

analyzing a certified reference material CRM-SA C Sandy Soil C. Student’s t-test was applied to the results obtained from the accuracy study as a statistical evaluation (Table 5) [40]. The results revealed good agreement between the observed value and certified value.


13

Table 6. The levels of Pd(II) in environmental samples (N: 3) (x U). Samplea Stream Solakli (Çaykara/Trabzon, Turkey) Sea water (Trabzon port)

Concentration (mg L1) BDLb 2.1 0.3

Samplec Soil (Trabzon, Turkey) Gold ore (Akoluk/Ordu, Turkey) Motorway dust (Trabzon, Turkey) Anodic sludge (Hes Cable/Kayseri, Turkey) Electronic waste (Trabzon, Turkey)d

Concentration (mg g1) BDL 4.2 0.6 BDL 19.2 2.8 40.4 6.2

a

Sample volume: 750 mL, Final volume: 2.0 mL. Below Detection Limit. c Sample quantity 0.5 g, Final volume: 2 mL. d Sample quantity 0.25 g, Final volume: 2 mL.


b

3.10 Application to real samples The method finally was applied to the real solid-liquid samples; stream water, sea water, soil, ore, motorway dust, anodic sludge and electronic waste. The results from the real samples are summarized in Table 6.

4. Conclusion The accurate and sensitive determination of Pd(II) and other noble metals in various materials usually requires their separation and pre-concentration from complex matrices. Metal cations can be determined using a variety of reagents because they have the ability to form complexes. However, it is very difficult to find or synthesize a ligand with high affinity to only one metal. PPTTMET, used in this study, was suitable only for determination of Pd(II) in acidic media. So, PPTTMET–Pd(II)/ Amberlite XAD-2010 combination SPE system was developed and optimized in terms of various analytical parameters. The system was simple, sensitive, fairly rapid, easy handling, accurate and precise, and also low cost. In addition to these features, this method presents an alternative procedure for the quantitative determination of Pd(II) at low concentration levels in various solid–liquid samples by FAAS. Also, Amberlite XAD-2010 resin loaded column could be used many times without any loss of its adsorption properties. In another aspect, the separation and pre-concentration of Pd(II) from highly salt content matrices could be successfully achieved by this method. The data that was obtained from the method proposed in this study have been compared with those of recently reported methods on determination of Pd(II) (Table 7). Distinguished features of the present work are that the LOD is low, the pre-concentration factor and adsorption capacity of the resin are relatively high when compared to several other solid phase extraction methods reported in the literature.

PF: Preconcentration factor.

Immobilized 2,6– TADAP/Dowex 50W X4 20/50 Amberlite XAD–2/ ODETA Amberlite XAD–2010/ PPTTMET

Mesoporous silicas/ MCM–41&MCM–48 Yeast Saccharomyces Cerevisiae/PdCl2 4 Octadecyl Bonded Silica/ HDPB Amberlite XAD–2/DHP Ion imprinted polymers/ VP–HEMA– EGDMA–AIBN Aminopropyl silica gel/ PET–SG

System

0.6

0.05 mol L1 HNO3

2.53

0.5 mol L1 H2SO4

5

0.59 1.5

pH 5–7 pH 4

pH 1.3

0.6

pH 1–10

4

0.54

pH 1.2

pH 2

0.1

pH 7

Medium acidity

LOD (mg L1)

6.2%

8%

55%

1.38%

3.32% 2.2%

1.2%

54%

51%

RSD

–

–

12.8

33

8.2 18.51

0.95

0.01

145

Adsorption capacity of resin (mg g1)

–

–

375

4100

34 60

200

125

4400

PF

Sample

Copper alloys and sulfide ores Motorway dust, anodic sludge, gold ore, industrial electronic waste material and water

Seawater, bronze coin and precious metal scraps Tap water samples

Synthetic solutions Street/fan blade dust samples

Al–Si–Pd catalysts

Wastewater and soil samples Road dust

Table 7. Comparison of the method with some recent solid phase extraction methods reported in the literature.


This work

[47]

[46]

[45]

[43] [44]

[42]

[41]

[9]

Ref

14 H. Serencam et al.


15

Acknowledgements Authors wish to thank Professor Neslihan Demirbas and Assistant Professor Duygu Ozdes for their contributions.


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