ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2015, том 70, № 6, с. 608-612
ОРИГИНАЛЬНЫЕ СТАТЬИ
y%K 543
LEAD PRECONCENTRATION AS RAC-(E,E)-N,N'-BIS(2-CHLOROBENZYLIDENE)CYCLOHEXANE-1,2-DIAMINE COMPLEXES FROM WATER AND TOBACCO SAMPLES BY DISPERSIVE LIQUID-LIQUID MICROEXTRACTION © 2015 Z. A. Alothman*, M. A. Habila*, E. Yilmaz**, I. Warad***, M. Soylak**, 1
*Advanced Materials Research Chair, Chemistry Department, College of Science, King Saud University
Riyadh-11451, Kingdom of Saudi Arabia **Erciyes University, Faculty of Sciences, Department of Chemistry 38039-Kayseri-Turkey 1E-mail: soylak@erciyes.edu.tr ***Chemistry Department, College of Science, King Saud University Riyadh-11451, Kingdom of Saudi Arabia Received 27.10.2013; in final form 23.12.2014
A dispersive liquid—liquid microextraction (DLLME) procedure for determination of Pb(II) in water and tobacco samples has been developed using rac-(E,E)-N,N'-bis(2-chlorobenzylidene)cyclohexane-1,2-diamine as a chelating agent. Factors influencing the efficiency of DLLME have been optimised, including metal solution pH, type and amount of dispersing solvent, type and amount of extraction solvent, amount of chelating agent and sample volume. The optimized conditions for maximum recovery were as follows: sample pH 6; dispersing solvent, 500 p.L of ethanol; extraction solvent, 150 p.L of chloroform; chelating agent, 150 p.L of 0.01% rac-(E,E)-N,N'-bis(2-chlorobenzylidene)cyclohexane-1,2-diamine; and sample volume, 15 mL. The method was validated using the certified reference material SPS-WW2 waste water. The method offered a limit of detection (LOD) of 2.6 ^g/L, a limit of quantification (LOQ) of 8.5 ^g/L, and a relative standard deviation (RSD) of 5.2%.
Keywords: dispersive liquid-liquid microextraction, AAS, lead, water and tobacco samples.
DOI: 10.7868/S004445021506002X
Recently, lead has attracted great interest of scientists and researchers worldwide. Lead is considered a toxic metal that can accumulate through the food chain, ending in the human body. Lead accumulation may lead to haematological disorders and the disturbance of metabolic processes [1, 2]. Lead may contaminate the human body through many routes, including dust, food and drinking water [3, 4]. The United States Environmental Protection Agency sets an action level of lead of15 ^g/L [5], while the World Health Organization sets a limit of 10 ^g/L [6]. These very low permitted lead concentrations in environmental samples have forced scientists to develop accurate, sensitive and precise methods for lead determination [7].
Sample preparation before instrumental analysis is very important for extracting the analyte and reducing matrix effects [8]. There are many methods for lead extraction, such as liquid—liquid extraction [9], solidphase extraction (SPE) [10], coprecipitation [11] and cloud point extraction [12]. However, the limitations of these methods, such as long analysis times, have limited their use [13]. Dispersive liquid—liquid mi-
croextraction is a fast, simple and accurate procedure for lead preconcentration [14—16]. DLLME is based on mixing an extraction solvent such as chloroform or carbon tetrachloride with a dispersing solvent. This mixture is injected rapidly into the sample solution; a cloudy suspension is obtained that includes the ana-lytes in its droplets, which then are separated by centrifuge and analysed [17, 18].
Liang and Sang [14] determined lead in biological samples such as human urine and water by DLLME using 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone as a chelating agent, achieving recoveries in the range 94— 101%. Zhou et al. [19] determined lead in water samples after preconcentration by DLLME using dithizone, which forms a complex with lead, achieving recoveries in the range of 93—97%. Soylak and Yilmaz [20] developed a ionic DLLME method for lead determination in water using pyrrolidine dithiocarbamate as a chelating agent and 1-hexyl-3-methylimidazolium hexafluorophosphate as the ionic liquid, achieving lead recovery of 100%. Alothman et al. [21] developed a temperature-controlled ionic liquid based microextraction (TC-IL-ME) method for ex-
LEAD PRECONCENTRATION
609
traction oflead(II) from hair samples, achieving recoveries of102—105%.
This work is aimed to develop a DLLME procedure using rac-(E,E)-N,N'-bis(2-chlorobenzylidene)cyclo-hexane-1,2-diamine [22] combined with atomic absorption spectrometry (AAs) to extract and preconcentrate lead from water and tobacco samples. Factors influencing the efficiency of DLLME have been optimised, including pH, type and amount of dispersing solvent, type and amount of extraction solvent, amount of chelating agent and sample volume.
EXPERIMENTAL
Chemicals and reagents. All reagents and chemicals were of analytical grade. Distilled and deionised water used prepared using a Millipore Milli-Q system with 18 MQ/cm resistivity. Standard solutions of Pb(II) (1000 mg/L) were prepared by dissolving the nitrate salt (Merck) in water. Working standard solutions were obtained by serial dilution of the stock standard solution. A 0.1% (w/v) solution of rac-(E,E)-N,N'-bis(2-chlorobenzylidene)cyclohexane-1,2-diamine was prepared in methanol.
Instrumentation. A Perkin-Elmer 3110 flame atomic absorption spectrometer (Norwalk, CT, USA), with an air-acetylene flame and a hollow cathode lamp, was used for measurement of lead ions. Instrumental parameters were as recommended by the manufacturer. Extractants were diluted in HNO3 and injected into the AAS using a Teflon funnel with a homemade micro sample introduction system and the absorbance was determined by peak height in continuous aspiration mode [20, 23]. Sartorious PT-10 pH meter (Germany) combined with a glass electrode was used for pH measurements. An ALC PK 120 Model centrifuge (Buckinghamshire, England) was used for centrifugation.
DLLME procedure. A lead solution (15 mL) was placed in a 50-mL centrifuge tube, 2 mL of phosphate buffer was added and the pH of the sample was adjusted to 6.0 using dilute NaOH and HCl solutions. rac-(E,E)-N,N'-Bis(2-chlorobenzylidene)cyclohexane-1,2-diamine (150 ^L, 0.01%) was added. Dispersing solvent (0.5 mL of ethanol) containing 150 ^L chloroform as the extraction solvent was then injected rapidly into the sample using a 5.0-mL syringe. A cloudy suspension formed swiftly, and Pb ions were extracted into fine droplets of chloroform in a few seconds. The mixture was immediately centrifuged for 10 min at 4000 rpm. The upper aqueous phase was removed with a syringe, the extractant was diluted to 200 ^L with concentrated HNO3, and 50 ^L of the solution was introduced into the FAAS nebuliser using a microinjection system to measure lead concentration.
Applications to real samples. Water samples including tap water, river, dam, waste water sources and lake water were collected from Kayseri in Turkey. Samples were passed through cellulose membrane filters with
100 r
80
>; 60
<D >
o o
R
40
20
8
pH
Fig. 1. Influence of pH on the recovery of Pb(II) (n = 3).
0.45-^m pores (Millipore). The analytical procedure presented above was used for all samples. The same procedures were also applied to the certified reference material SDS-WW2 waste water.
Tobacco samples were collected from the Kayseri market in Turkey and digested as described in [10]. Briefly, tobacco samples were washed with deionised water and dried at 60°C; then, 0.5 g samples were weighed separately into beakers. Concentrated nitric acid (15 mL) was added to the beakers, which were heated on a hot plate at 100°C to dryness. The residues were cooled, concentrated HNO3 (10 mL) and H2O2 (5 mL) were added, and the solutions were heated to dryness. The mixtures were dissolved in water, filtered through blue band filter paper and analyzed by the proposed method as for the real samples.
RESULTS AND DISCUSSION
Herein, the DLLME using new chelating agent was optimised to separate and preconcentrate lead from environmental samples. The efficiency of the method was improved by evaluating the influence of key parameters such as metal solution pH, type and amount of dispersing solvent, type and amount of extraction solvent, amount of chelating agent, sample volume and presence or absence of matrix.
Influence of pH. It was reported in early studies that pH is an effective parameter for optimisation of DLLME [20, 21-24]. Therefore, the influence ofPb(II) solution acidity on recovery percent of DLLME was evaluated in the pH range 2-8. The results in Fig. 1 reveal that quantitative recovery was obtained at a pH of 6. In highly acidic solution, the recovery was not quantitative. Thus, a Pb(II) solution at pH 6 was selected for further study.
Influence of dispersing solvent and amount. To maximise recovery, the effect of the dispersing solvent was studied. Methanol, ethanol, propanol, acetone and ac-etonitrile were tested; recoveries are presented in Fig. 2. The quantitative recovery (99%) was achieved in ethanol. Methanol and acetonitrile gave the lowest recoveries:
0
2
3
4
5
6
7
100
80
¡>? 60 £
§ 40
Рй
20
0
Methanol Ethanol Propanol Aceonitrile Acetone Dispersing solvent
Fig. 2. Influence of dispersing solvent type on the recovery of Pb(II) (n = 3).
100
80
<D >
О О
* 60
100 200 Chloroform volume,
300
Fig. 3. Influence of the volume of chloroform on the recovery of Pb(II) (n = 3).
100
E?
e v o
о
e
РЙ
80
60
40
100 200 Ligand volume,
300
Fig. 4. Influence of ligand amount on the recovery of Pb(II) (n = 3).
1001
E? 80
e v o
о
e
РЙ
60 -
40
10
20 30
Sample volume, mL
40
Fig. 5. Influence of sample volume on the recovery of Pb(II) (n = 3).
40 and 59%, respectively. These results were in agreement with those reported by Liang and Sang [14] and Zhou et al. [19] who reported that the highest recoveries were obtained using ethanol as dispersing solvent.
In addition, different volumes of ethanol were tested (0.4, 0.5, 1.0, 1.5, 2.0, and 3.0 mL), giving recoveries
Для дальнейшего прочтения статьи необходимо приобрести полный текст. Статьи высылаются в формате PDF на указанную при оплате почту. Время доставки составляет менее 10 минут. Стоимость одной статьи — 150 рублей.