ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2009, том 64, № 6, с. 627-632
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УДК 543
ATOMIC ABSORPTION SPECTROMETRIC DETERMINATION OF CD(II), MN(II), NI(II), PB(II) AND ZN(II) IONS IN WATER, FERTILIZER AND TEA SAMPLES AFTER PRECONCENTRATION ON AMBERLITE XAD-1180 RESIN LOADED WITH L-(2-PYRIDYLAZO)-2-NAPHTHOL
© 2009 O. Hazer, S. Kartal, S. Tokahoglu
Erciyes University, Faculty of Arts and Sciences, Department of Chemistry 38039, Kayseri, Turkey
Receired 30.11.2007; in final form 25.11.2008
A new chelating resin, l-(2-pyridylazo)-2-naphthol (PAN) coated on Amberlite XAD-1180 (AXAD-1180), was prepared and used for the preconcentration of Cd(II), Mn(II), Ni(II), Pb(II) and Zn(II) ions prior to their determination by flame atomic absorption spectrometry (FAAS). The optimum pH for simultaneous retention of the elements and the best eluent for their simultaneous elution were pH 9.5 and 3 M HNO3, respectively. The sorption capacity of the resin was found to be 5.3 mg/g for Cd and 3.7 mg/g for Ni. The detection limits for Cd(II), Mn(II), Ni(II), Pb(II) and Zn(II) were 0.7, 10, 3.1, 29 and 0.8 |g/L, respectively. The effects of interfering ions on quantitative sorption of the metal ions were investigated. The preconcentration factors of the method were in the range of 10-30. The recoveries obtained were quantitative (>95%). The standard reference material (GBW07605 Tea sample) was analysed for accuracy of the described method. The proposed method was successfully applied to the analysis of various water, urea fertilizer and tea samples.
As the number of ecological and health problems are associated with environmental contamination continues to rise, the determination of heavy metal ions present at trace levels in environmental samples is gaining great importance [1]. Nickel is a moderately toxic element as compared with other transition metals. However, it is known that inhalation of nickel and its compounds can lead to serious health problems, including respiratory system cancer. Moreover, nickel can cause a skin disorder known as nickel-eczema [2]. Manganese is a necessity for the proper function of several enzymes and an essential micro-nutrient for the function of the brain, nervous system, and normal bone growth. It optimizes enzyme and membrane transport functions [3]. Cadmium is known to be highly toxic for animals, plants and humans even at low concentrations and can be accumulated in several organs. The most important anthropogenic sources of this element include emissions from industrial plants, such as zinc smelters, steel works, incinerators and power stations [4].
Zinc is an essential trace element of great importance for humans, plants and animals. Zinc deficiency slows growth and development of the neonate and also leads to cognitive defects and impairs the immune system. An excess of this metal can play an important role in the progression of several damages to human body, including distur-
bances in energy metabolism or increasing in oxidative stress [5, 6].
Lead is one of the most widespread heavy metals in the environment, in view of its extensive use in storage batteries, solders, cable sheaths, pigments, anti-knock products and radiation shields and due to corrosion of household plumbing systems and erosion of natural deposits. The consumption of lead-contaminated drinking water causes delay in physical or mental development, slight deficit in learning abilities of children, high blood pressure and kidney problems in adults [7].
Despite the selectivity and sensitivity of analytical techniques such as atomic absorption spectrometry, there is a crucial need for the separation and preconcentration of trace elements before their analyses due to their low concentrations in numerous samples. In trace analysis, preconcentration and/or separation of trace elements from the matrix is frequently necessary to improve the detection limit and selectivity for their determinations by FAAS. For this purpose, several methods have been proposed and used for preconcentration and separation of trace elements according to the nature of the samples, the concentrations of the analytes and the measurement techniques [1, 8, 9]. These include ion exchange, solvent extraction, coprecipitation, cloud point extraction, electrodeposition and solid phase extraction (SPE).
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Fig. 1. Effect of pH on the recovery of Cd(II), Ni(II), Mn(II), Pb(II) and Zn(II) ions (sample volume: 50 mL, eluent: 30 mL of 3 M HNO3, amount of the ions: 3.0 |lg Cd(II), 12.5 |lg Ni(II), 7.5 |lg Mn(II), 30 |lg Pb(II) and 1.5 |lg Zn(II)).
Although liquid-liquid extraction has proven to be a reliable and efficient technique, it is a time, reagent and labour consuming procedure, which can not be easily automated. SPE employs similar principles of metal partitioning between solid and liquid phases. It is one of the most effective procedures for trace metal analysis because it is an attractive technique that reduces consumption of reagents and exposure to solvents and disposal costs. The retention of trace elements on sorbents requires the addition of a ligand to the sample or ligand attachment to the sorbent by physical adsorption (impregnation) or chemical bonding (immobilization) [10, 11]. A number of reagents have been investigated for impregnation of sorbents as a means of increasing retention capacity and selectivity of the sor-bent for trace elements [12-15]. Various adsorbents such as activated carbon [16], silica gel [17], chelating resins [18], polyurethane foam [19] and Amberlite XAD resins [20-22] have been used to preconcentrate trace metal ions. Amberlite XAD resins are good supports for developing chelating matrices. Their attractive features are easy regeneration for multiple sorption-desorption cycles, good mechanical stability and reproducible sorption characteristics. In comparison to silica gel and cellulose, the kinetics of sorption is faster [23].
l-(2-Pyridylazo)-2-naphthol forms stable complexes with many transition metals of interest; it is one of the most extensively used complexing agents for trace element analysis. Its solutions are stable. In acidic solutions the pyridine nitrogen is protonated and in basic solutions the proton of the OH group is ionized. The metal chelates of PAN have the metal atom bonded to 0 of the OH group, to pyridine N and to azo N [24].
In this paper, a new separation/preconcentration method is described for the determination of Cd(II), Mn(II), Ni(II), Pb(II) and Zn(II) ions in the water, fertilizer, tea and certified tea samples (GBW07605) by FAAS using Amberlite XAD-1180 resin loaded with PAN.
EXPERIMENTAL
Instruments. A Perkin Elmer 3110 model atomic absorption spectrometer equipped with single element hollow cathode lamps and air-acetylene burner, Shelton, USA was used for the determination of metals. The instrumental parameters were used according to the manufacturer's recommendations. The wavelenghts (nm) selected for the determination of the analytes were as follows: Cd 228.8, Mn 279.5, Ni 232.0, Pb 283.3 and Zn 213.9. A Jenco model 672 digital pH meter (San Diego, CA, USA) was used for the pH adjustments.
Reagents and solutions. All chemicals were of analytical reagent grade (Merck, Darmstadt, Germany). Dis-tilled-deionized water was used in all experiments. Stock solutions (1000 mg/L) of the elements were prepared by dissolving appropriate amounts of their nitrate salts in 1.0 % (v/v) hn03 and further diluted daily prior to use. l-(2-Pyridylazo)-2-naphthol reagent was used as purchased. The following buffer solutions were used for the solid phase extraction procedures: CH3COOH/CH3COONa buffer for pH 4; Na2HPO4/NaH2PO4 buffer for pH 7; and NH3/NH4CI buffer for pH 9-11. Non-ionic Amberlite XAD-1180 resin (Acros Organics, NJ, USA) is a polystyrene divinylbenzene copolymer (surface area 500 m2/g, average pore size 400 A and average particle diameter 530 |m). Prior to use it was washed with hydrochloric acid and ethanol and then rinsed with water until obtaining a neutral solution and then dried at 105°C in an oven.
20 mL of 0.1% (w/v) PAN solution were passed through a glass column (10 cm long, 1 cm i. d.) containing 0.5 g AXAD-1180 resin at a flow rate of 1 mL/min for the preparation of the AXAD-1180 resin loaded with PAN. The impregnated resin was rinsed with distilled water and conditioned with 10-15 mL of pH 9.5 buffer solution prior to passage of the sample solution.
Proposed preconcentration procedure. The method was tested with model solutions prior to the determination of the trace metals in the real samples. A 50 mL aliquot of the model solution containing 3.0 |g Cd(II), 7.5 |g Mn(II), 12.5 |g Ni(II), 30 |g Pb(II) and 1.5 |g Zn(II) ions was passed through the column at a flow rate of 1 mL/min after adjusting the pH to 9.5. The retained metal ions were eluted with 30 mL of 3 M HNO3. The eluate was evaporated to 0.5-1 mL on a hot plate. The residue was dissolved and diluted to 5 mL with 3 M HNO3 solution. The concentration of the metal ions in the final solution was determined by FAAS.
Collection and preparation of samples. Treated black Turkish tea sample was purchased from a local market. The urea fertilizer sample was purchased from Kayseri, Turkey. 3.0 g of the sample was dissolved in 1 M of nitric acid and diluted to 50 mL with water. The stream water and tap water samples were collected from Yozgat, Turkey. The water samples were filtered through a cellulose membrane filter (Millipore), 0.45 |m pore size, to remove par-ticulate matter, and then acidified with cone. HNO3 (5 mL per 1 liter of water sample).
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Fig. 2. Effect of the sample flow rate on the recovery of analytes (n = 3).
To dissolve the certified reference material (GBW07605 Tea sample) and the tea sample, an aliquot of 0.5 g of each sample was taken into a 250 mL of
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