Carbamatos

Supercritical Fluid Extraction of Carbamate Pesticides from Soils and Cereals
A. Izquierdo / M. T. Tena / M. D. L u q u e de Castro / M. Valcfircel* Department of Analytical Chemistry, Faculty of Sciences University of C6rdoba, 14004 C6rdoba, Spain

Key Words
Column liquid chromatography Supercritical fluid extraction Carbamate pesticides Soils Cereal

secreted in milk, so they areextensively used in forage treatments. Thanks to their low persistence, high effectiveness and low phytotoxicity, they are widely employed in agriculture, particularly in food crop applications [1]. N-methylcarbamates are hydrolysed by NaOH at elevated temperatures to yield methylamine, which subsequently reacts with o-phthalaldehyde (OPA) and 2mercaptoethanol at high pH to produce the highly fluorescentisoindole. The use of these reactions in a 2stage, post-column derivatization system for N-methylcarbamates was first reported by Moye et al. [2] and Krause [3] in the late 70's and later by Hill et al. [4] for screening well water samples. The procedure was subsequently adopted as an official method for drinking water by the EPA [5]. Supercritical fluid extraction (SFE) has been successfullyapplied to environmental analysis as a practical alternative to traditional methods employing liquid solvents [6-7]. The potential of SFE coupled with SFC for the isolation of sulphonylurea herbicides from soil and plant materials was demonstrated long ago by McNally et al. [8]. SFE-SFC has also been used by the same authors [9] for the determination of phenylurea herbicides (Linuron and Diuron) insassafras soil. s-Triazine herbicides [10] were also quantitatively recovered from soil sediment with pure CO2 (with the exception of simazine, which required addition of methanol to the SFE cell). SFE is specially recommended for thermally labile compounds such as phenylurea herbicides [11]. The influence of the soil matrix on quantitative removal of atrazine, its biodegradation products andchlorotriazines, has been studied by Steinheimer et al. [12]. Cortes et al. [13] developed an on line SFE-LC-GC system for the determination of the insecticide chlorpyrifos in grass field samples with a mean recovery of 97.5 % and an r.s.d, of 10.8 %. The system minimizes the use of organic solvent (less than 0.1 ml is required for the entire analytical procedure), and also analyte loss and samplecontamination because the coupled assembly simplifies sample handling. SFE using CO2-3 % methanol was compared with sonication and with Soxhlet extraction of organoOriginal

Summary
A method for the supercritical fluid extraction of carbamate pesticides (propoxur, aminocarb, carbaryl and methiocarb) from soil and cereal samples using CO2 is proposed. Extractions were at 378 bar and 54 ~ Analyteswere determined in the extracts by HPLC with fluorescence detection after post-column derivatization. Recoveries from spiked soil ranged between 39.6 and 91.7 %, depending on analyte and soil components. Lowest recoveries were from sandy soils. Aminocarb could not be recovered from any soil using CO2. Recovery of aminocarb from diatomaceous earth was improved by adding methanol to the extraction cellprior to SFE, but the effect was not observed in soil samples. Recoveries for propoxur and aminocarb from spiked wheat were about 75 %, and only between 3050 % for aminocarb from corn and oats, and carbaryl from wheat. Fat was coextracted using CO2 and retained in the trap together with the analytes, however, appropriate rinsing solvent allowed on-line clean-up of the extract.

IntroductionCarbamates, together with organochlorine and organophosphorous compounds, are the three major classes of synthetic organic insecticides in use today. Carbamates are non-systemic pesticides which exhibit strong cholinergic effects on insects and some animal species. They are rapidly detoxified and eliminated in animal urine; also, they are not concentrated in fat nor 206 0009-5893/96/02 0206-07 $...