Determination of imidacloprid and its metabolite 6-chloronicotinic acid in greenhouse air by high-performance liquid chromatography with diode-array detection
Introduction
Imidacloprid [1-6(chloro-3-pyridylmethyl)-N-nitioimidazolidin-2-ylideneamine] belongs to a new group of active ingredients, the chlornicotinyl insecticides. It has a new mode of action, low toxicity to warm-blooded animals, good systemic properties and a lasting action [1]. The development, activity, mode of action and effectiveness have been described by Leicht [2] and its physical, chemical and toxicological properties have been summarised in the pesticide manual [3]. The compound was introduced in Europe by Bayer (Leverkusen, Germany). The parent and its main metabolite (6-chloronicotinic acid) are polar compounds with high solubility in water.
Residues of imidacloprid are analysed commonly by HPLC with UV detection [4], although pulse reductive amperometric detection has been also used [5]. However, some papers have been found using GLC based techniques [6] but derivatization is required. Other methods, such as a photochemical-fluorimetric method [7] or a differential pulse polarographic method [8] have been proposed. Several works have been published for the determination of imidacloprid residues in different matrices, such as vegetables [9], [10], waters [6], [7], [11], and soils [6], [12], [13]. No methods have been published for the determination of residues of this insecticide and its metabolite in air.
Nowadays the potential risk of exposure to pesticide residues in working environments is high. On one hand, pesticide use has increased dramatically in and around businesses and homes through applications by professional laws care and pest control firms and by homeowners. Many of these applications are performed routinely on a weekly or monthly to using insecticides. Depending upon the type of work performed, individuals can spend long hours in an indoor environment where they come in contact with pesticide residues from both dermal and inhalation exposures. In addition, greenhouse operations involve heavy use of pesticides to control pests, and the potential for worker exposure is high. Safety measures for farm workers (mainly small-holders) are very poor until now. Many of them do not strictly follow the manufacturer’s directions in using the formulations.
On the other hand, regulations concerning acceptable levels of insecticides in air in working environments have been in place for years because of the potentially high residue levels that might be encountered during a working day [14], as average eight hours.
The EPA Air program is poised for growth and change. Implementation of the clean Air Act amendments will require new methods and regulations [15]. Information on current contaminants and their pervasiveness will be required to assess the state of air quality. Routine monitoring will require the development of rugged methods suitable for a great variety of situations.
In order to evaluate the exposure to pesticides, accurate, reliable and sensitive analytical methods for monitoring organic trace constituents in the atmosphere are necessary. For air analysis, the sampling procedure is of even greater importance as a key step in obtaining reliable measurements than for most other environmental media [16].
Methods of preconcentration as adsorption on solids is becoming more widely employed because of its advantages in the selection of the most appropriate sorbent or a given group of pollutants [17], [18]. Diffusive air sampling using prepacked adsorbents in sample tubes has been used extensively in environmental applications. It has been extended successfully to other environmental application for air and water sampling in Europe.
As part of a project for monitoring pollutants in air, we are interested in the development of a method for the determination of imidacloprid and its metabolite 6-chloronicotinic acid in air samples by HPLC–DAD. This technique is particularly suitable in this case due to their strong absorbance between 200 and 270 nm.
This paper reports the results of studies carried out with different solid sorbents and using several extraction procedures in order to establish the optimum conditions for sampling and analysing imidacloprid and 6-chloronicotinic acid in greenhouse air. The development and validation of the methodology using standard pesticide vapours was also described.
The procedure was applied to the determination of the mentioned pesticides in air, after an experimental application carried out in a greenhouse with a high volume application system in the Nijar zone (Almerı́a, Spain).
Section snippets
Chemicals and solvents
HPLC grade solvents were used. The pesticide standards (Pestanal quality) were obtained from Riedel-de Haën (Seelze, Germany). Solid standards were dissolved in acetonitrile at the concentration level of 200 μg ml−1 and stored at 4°C in the dark, where they were stable for several months. Working solutions of the pesticides with concentrations ranging from 0.25 to 5.0 μg ml−1 were prepared daily by appropriate dilution in the mobile phase. Mobile phase was degassed with helium prior to use.
Results and discussion
Imidacloprid and 6-chloronicotinic acid pesticides are polar compounds with high molar absorptivity in the UV–Vis region. They display absorption spectra with absorption maxima located at 210 and 270 nm for imidacloprid and 200, 227 and 270 nm for 6-chloronicotinic acid. For this reason, HPLC with diode-array detection is one of the primary detectors used in their determination. In addition, the advent of DAD increases the utility of absorbance detectors due to the spectral confirmation
Conclusions
A method has been developed to sample and analyse imidacloprid an 6-chloronicotinic acid in greenhouse air using personal samplers connected to XAD-2 cartridges as sampling media, acetonitrile and buffer to extract the analytes from the sorbent and HPLC–DAD analysis. Analytical parameters of methodology have been validated using standard pesticide vapours. Finally an application in a greenhouse showed that the concentration of imidacloprid in the air is very low and descends to below the
Acknowledgements
This study has been financially supported by the European Union Standard Measurement and Testing Programme, contract number SMT4-CT96-2048 and by the CICYT Project AMB97-1194-CE.
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2014, Ecological IndicatorsCitation Excerpt :Conversely, since frogs represent important natural enemies of several agricultural pests, they might be exposed to the residual pesticides in pests through the food chain. Several reports agree, demonstrating that IMI residues can be found in vegetables, crops, and fruits, as well as in pests (Fernandez-Alba et al., 1996; Garrido Frenich et al., 2000; Ko et al., 2014). Our observations revealed 84.91 mg/L (confidence limit, 77.20–93.04) as the 96 h LC50 value of IMI for H. pulchellus tadpoles.
Development of a simple extraction and oxidation procedure for the residue analysis of imidacloprid and its metabolites in lettuce using gas chromatography
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Separation of imidacloprid and its degradation products using reversed phase liquid chromatography with water rich mobile phases
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