ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2015, том 70, № 1, с. 15-19
ОРИГИНАЛЬНЫЕ СТАТЬИ ^
УДК 543
SIMULTANEOUS DERIVATIZATION/PRE-CONCENTRATION OF 3-PHENOXYBENZALDEHYDE AS TRANSFORMATION PRODUCT OF PERMETHRIN WITH 2,4-DINITROPHENYLHYDRAZINE BY SOLID PHASE EXTRACTION AND SPECTROPHOTOMETRIC DETECTION © 2015 Mahboubeh Saeidi*, 1, Zeinab Ykzdani*, Fatemeh Sabermahani**
* Department of Chemistry, Vali-e-Asr University of Rafsanjan Rafsanjan, Iran 1E-mail: Saeidi@vru.ac.ir **Department of Chemistry, Payame Noor University PO BOX19395-4697, Tehran, Iran Received 31.10.2012; in final form 17.08.2013
A simple, cheap and sensitive solid phase extraction method has been described for simultaneous derivatiza-tion and preconcentration of 3-phenoxybenzaldehyde (3-pbAl) in aqueous samples. The method is based on the reaction of 3-pbAl with 2,4-dinitrophenylhydrazine (DNPH) to form 2,4-dinitrophenyhydrazone in a column packed with silica gel. Using 100 mg of the sorbent, this compound was sorbed at pH 3 and recovered with 4 mL acetonitrile prior to its spectrophotometric determination at 407 nm. The effect of DNPH concentration, pH, sample flow rate and volume, elution conditions and foreign ions has been investigated. A preconcentration factor of 25 was achieved by passing 100 mL of sample through the column. The relative standard deviation for 5 replicate analyses at three concentration levels of 3-pbAl was from 0.34 to 1.12%.The calibration curve was linear from 0.01 to 5 p.g/mL of 3-pbAl, and limit of detection(S/N = 3) was 1.4 ng/mL. Molar absorptivity was found to be 4.7 x 104 L/mol cm.
Keywords: permethrin, 3-phenoxybenzaldehyde, 2,4-dinitrophenylhydrazine, solid phase extraction, spec-trophotometry.
DOI: 10.7868/S0044450215010120
Permethrin[3-phenoxybenzyl(1RS)-cis,trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecar-boxylate] [1, 2] is the most popular synthetic pyre-throid insecticide used in agriculture, forestry, homes, horticulture, veterinary and public health programs [3] thatpresents two diastereomers with different chemical, physical and toxicological properties [4]. Pyrethroids are synthetic insecticides having chemical structures similar to the natural chemicals, pyrethrins, which are produced by the flowers of pyre-thrums, the old world plants of the genus chrysanthemum (C. Cinerariaefoliume and C. Coccineum) [5, 6]. Pyrethroids are used extensively worldwide in agriculture and as pest-control agents in household applications. They are effective against a broad range of pests and are stable under field conditions [7]. The basic structure of these pesticides can be characterized as an acid joined to an alcohol by an ester bond. Due to their potent neurotoxic activity against insects but low tox-icity for mammals, pyrethroids are generally regarded as a replacement for more toxic or recalcitrant orga-nochlorines or organophosphates [8]. The synthetic pyrethroids can cause serious health effects to human
such as paraesthesia, headache, dizziness, nausea and skin irritations [6]. Permethrin is nontoxic to mammals, being highly toxic to some no target insects such as honeybees and other beneficial insects. This compound has apparent toxic effects to some aquatic species such as fish, aquatic insects, crayfish and shrimp at parts per billion levels. Its high octanol—water partition coefficient (log KOW = 6.1) suggests that it may have a tendency to bioaccumulation in living organisms [9]. However, with the increasing use of pyrethroids, the significance of ecological safety and health risk is an emerging concern [6].
Pesticide transformation products (TPs), both metabolites and degradates, are also an issue of concern because they may feature harmful properties comparable to or higher than those of the active parent substance [10]. Currently, there is an increasing concern regarding the formation of TPs since there are evidences indicating that these products can be more toxic and persistent than the parent compounds [11]. Moreover, TPs can have different properties that enable them to occur in environmental areas not reached by the pesticide itself. For instance, due to their mobil-
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MAHBOUBEH SAEIDI и др.
Absorbance
Wavelength, nm
Fig. 1. Absorption spectra in visible region (in the optimum conditions) of derivative compound from reaction of 3-pbAl with DNPH (1) and of 3-pbAl (2).Conditions: c3-pbAl = 5 mg/L, Fdnph = 3.5 mL, Cdnph = 10.5 mM, pH 3, sample flow rate 0.6 mL/min, elution flow rate 1 mL/min, Feluent = 4 mL, amount of sorbent 0.1 g.
ity in the soil—water environment, TPs can reach groundwater more easily than parent compounds [11, 12]. In consequence, there is a need for developing analytical methodologies in order to monitor TPs in environment, food matrices and water samples. Most pyre-throids can be converted to 3-pbAl, a toxic metabolite that is refractory to microbial degradation [13—15]. So, 3-pbAl is a toxic and persistent metabolite of per-methrin that was studied in this work.
The development of quick, simple and inexpensive methods for the determination of different pollutants such as pesticides and their degradation products in the environment has always been important to ecotox-icologists. However, as the number of pollutants in circulation has increased, the need for such methods has grown [16]. Solid phase extraction (SPE) is an attractive method that reduces consumption of and exposure to solvent, disposal costs and extraction time [17].
Several techniques have been reported for determination of permethrin and its degradation products, which relied upon gas chromatography [18—21], HPLC [4, 22-24], GC-MS [2, 7] and immunoassay techniques [3, 25, 26]. Most of them are intended for determination of multi residues of pyrethroids in environmental matrices, crops and food of animal origin. Surprisingly, very little spectrophotometric works in assaying permethrin and its degradation product have been reported.
The aim of this study is to develop a method for the simultaneous DNPH-derivatization and preconcen-tration of 3-pbAl in aqueous samples by using SPE. In this method, 3-pbAl was reacted with DNPH to form
2,4-dinitrophenylhydrazone. This colored derivative was extracted from aqueous solution by SPE on silica gel sorbent and eluted with acetonitrile. Detection was done with spectrophotometry.
EXPERIMENTAL
Reagents and solutions. All solvents and reagents were of analytical grade and used without further purification. Deionized water was used throughout the experiment. 3-PbAl was purchased from Fluka. Silica gel (0.063-0.2 mm or 70-230 mesh) (Merck, Darmstadt, Germany) was used as sorbent. Other solvents and reagents were supplied by Merck (Darmstadt, Germany).
Standard stock solution of 3-pbAl with a concentration of 100 |g/mL was prepared by dissolving an appropriate amount in ethanol. Working standard was prepared daily by dilution of the stock solution with deionized water as required. Stock DNPH solution, 60.0 mM, was made by dissolving 594.4 mg of the de-rivatizing reagent in 50.0 mL of concentrated sulfuric acid-water-acetonitrile (ACN) solution (2 : 5 : 1). A solution containing 10.5 mM DNPH was prepared by appropriate dilution of the stock solution with deionized water. All solutions were stored at 4°C.
Instruments. A UV-visible spectrophotometer (Cary 100, Varian, and Australia) equipped with 1 cm cells was used for all absorbance measurements. A pH meter (Lab 722, Metrohm, Switzerland) was used for adjusting the pH of sample solutions.
General procedure. An aliquot of 3-pbAl (0.1575.0 |g) was taken, pH of the solution was adjusted to 3 with diluted HCl and then diluted was done to the final volume of 15 mL. The column was packed with 100 mg of the silica gel as sorbent and conditioned with deionized water. The 3-pbAl solution was fed into the column and 3.5 mL of 10.5 mM DNPH was added. It was then passed through the column at a flow rate 0.6 mL/min. In the elution step, 4 mL CH3CN was passed through the column at a flow rate 1 mL/min. Absorbance of this solution was measured with UV-visible spectrophotometer at 407 nm. This procedure required blank measurement.
RESULTS AND DISCUSSION
Preliminary experiments showed that 3-pbAl had no peak in visible region but the absorption spectrum of colored derivative, 2,4-dinitrophenylhydrazone, had a maximum at 407 nm (Fig. 1).Therefore this wavelength was selected for all absorbance measurements. On the other hand, since DNPH had absorption peak in the visible region, all measurements were done against reagent blank. In order to achieve the best performance, the derivatization/preconcentration procedure was optimized for various analytical parameters, such as effect of DNPH, pH of the sample, the flow rate of sam-
ple solution, amount of sorbent, type, volume and flow rate of the eluent and sample volume.
Effect of DNPH. The concentration of DNPH is an important variable. Initial experiments were conducted to establish the influence of the volume of the DNPH solution. The optimum volume of DNPH is 3.5 mL. In this condition, the concentration of DNPH was studied over the range 10.0—11.0 mM. As it can be seen from Fig. 2, the absorbance increased when the concentration ofDNPH increased to 10.5 mM and then decreased. This concentration was selected as optimal. The decrease in the absorbance at DNPH concentrations higher than optimal can be ascribed to possible interference of excess DNPH on the adsorption of hydrazone.
Effect of the sample pH. The sample pH is another significant variable. Its influence was examined by using 15 mL volume of 3-pbAl that was adjusted to pH value from 2—8 with diluted hydrochloric acid. As can be seen in Fig. 3, a maximum absorbance was observed at pH 3.0. The decrease in absorbance at higher pH values can be ascribed to the full deprotonation ofthe hydrazine group ofthe DNPH (pKa = 2.2) which probably hinders acid catalyzed derivatization of aldehyde to form corresponding hydrazone. F
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