Ultrasonic solvent extraction of pesticides from soil

doi:10.1016/S0021-9673(98)00301-X

Journal of Chromatography A

Volume 823, Issues 1–2, 9 October 1998, Pages 3-9

https://doi.org/10.1016/S0021-9673(98)00301-X Get rights and content

Abstract

Ultrasonic solvent extraction of the pesticides atrazine, propham, chlorpropham, diflubenzuron, α-cypermethrin and tetramethrin from soil is reported. The extraction procedure was optimized with regard to the amount of solvent, the duration of sonication and the number of extraction steps. Ultrasonic solvent extraction was compared with traditional extraction methods, shake-flask and Soxhlet extraction. The recovery of pesticides was determined by quantitative thin-layer chromatography on RP-18 plates. Ultrasonic extraction using acetone showed satisfactory extraction efficiencies combined with simplicity of use and low solvent consumption.

Introduction

The use of pesticides constitutes an important aspect of modern agriculture. Agrochemicals are used to control pests like insects, plant diseases, worms and rodents. When pesticides are released into the environment they may be broken down, or they may resist degradation and thus remain unchanged in the environment for long periods of time [1].

The increasing number of environmentally significant pesticides requires the development of an analytical method that allows simultaneous determination of different pesticides with minimum extraction and clean-up steps.

Thin-layer chromatography (TLC) is now widely accepted as a rapid and efficient screening technique. It has grown rapidly in recent years because of improvements in the instrumentation for spotting and densitometric evaluation, and in the development of sorbents and modified layers. Although other methods are widely used for pesticide determination, e.g. gas chromatography, supercritical fluid chromatography, spectrometry, enzyme immunoassay and capillary electrophoresis, TLC has retained its status as a valid and simple method for quantitative and qualitative analysis of pesticides and their metabolites 2, 3.

Chromatographic analysis usually follows tedious sample preparation to extract compounds to be analyzed from complex matrices, e.g., soil, plant materials and foods. For the isolation of pesticides from soil samples various extraction and clean-up procedures have been proposed. Almost all traditional methods (shake-flask, Soxhlet etc.) are time- and solvent-consuming. Due to the long extraction process, degradation of the components can occur. Typical solvent volumes can range from 50 ml to more than 400 ml per sample. A number of methods such as ultrasonic solvent extraction, solid-phase extraction (SPE), supercritical fluid extraction (SFE), accelerated solvent extraction, microwave extraction, SPME, etc., were proposed to resolve the solvent-consumption problem.

The aim of this work was to optimize the condition of ultrasonic solvent extraction for six most commonly used pesticides for weed and insect control, from soil samples. Sonication provides a more efficient contact between the solid and solvent than shake-flask method, usually resulting in a greater recovery of analyte [4]. The extraction procedure was optimized with regard to the solvent amount, the duration of sonication and the number of extraction steps. A comparative study on the extraction of α-cypermethrin, tetramethrin, diflubenzuron, chlorpropham, propham and atrazine from soil was conducted employing the ultrasonic technique, Soxhlet extraction and shake-flask method with various solvents. The extracted pesticides were identified and quantified using reversed-phase TLC-densitometry.

Section snippets

Materials

All pesticide standards at least 98% purity were furnished by various pesticide manufactures. Pesticide investigated and their characteristics are listed in Table 1. All solvents were of analytical reagent grade supplied by Kemika (Zagreb, Croatia). Soil was collected at hill Medvednica near Zagreb. It was not treated with any agrochemicals for at least 10 years before collection.

Preparation of standard solution

Stock solution of pesticide mixture was prepared by dissolving accurate amounts of powdered samples in methanol.

Results and discussion

Quantitative evaluation of chromatograms was performed by measuring the absorbance of the analyte spots at 254 nm. The calibration function of peak area against mass concentration of each pesticide was plotted. The regression lines, correlation coefficients, limit of detection and linear functional correlations are summarized in Table 2.

In case of the analyte being present in low concentration in complex sample, such as soil or biological plant material, extraction and concentration procedures

Conclusion

The results obtained indicate that the ultrasonic solvent extraction method is applicable to extraction of pesticides from soil. The ultrasonic solvent extraction is more rapid than conventional shake-flask or Soxhlet extraction methods, and the solvent consumption is significantly lower. Additionally, the extracts from sonication can be chromatographed without subsequent clean-up step, and the analysis time is considerably reduced.

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