Journal of Chromatography A, 795 (1998) 43–51 Comparison of different clean-up procedures for the determination of N-methylcarbamate insecticides in vegetable matrices by high- performance liquid chromatography with UV detection a b b c, * ´ G.S. Nunes , M.L. Ribeiro , L. Polese , D. Barcelo a ˜ ˜ ´ Department of Technol. Chemistry, Fed. University of Maranhao / UFMA, Av. Portugueses s / n, 65080-040 Sao Luıs-Ma, Brazil b Institute of Chemistry / UNESP , C.P . 355, 14800-900 Araraquara SP , Brazil c Department of Environmental Chemistry, CID/ CSIC, Jordi Girona 18-26, 08034 Barcelona, Spain Abstract Several clean-up procedures which included the use of glass chromatography columns (silica gel, alumina, Florisil, silanized Celite–charcoal), Sep-Pak cartridges and standard solutions were compared for the determination of the following N-methylcarbamate (NMC) insecticides: aldicarb, carbaryl, carbofuran, methomyl and propoxur. According to recovery results of the compounds after elution in a glass column, the most efficient systems employed 4.6% deactivated alumina and a silanized Celite–charcoal (4:1) as adsorbents, using dichloromethane–methanol (99:1) and toluene–acetonitrile (75:25) mixtures, respectively, as binary eluents. The recoveries of the compounds studied varied from 84 to 120%. Comparable recoveries (75–100%) for Sep-Pak cartridges in normal phase (NH , CN) and reversed phase (C ) were observed. Different 2 8 temperatures were tested during the concentration step in a rotary evaporator, and we verified a strong influence of this parameter on the stability of some compounds, such as carbofuran and carbaryl. Recovery studies employing the best clean up procedures were performed at the Brazilian agricultural level in potato and carrot samples; validation methodology of the US Food and Drug Administration was adapted for the N-methylcarbamate analysis. Their recoveries ranged between 79 and 93% with coefficients of variation of 2.3–8%.  1998 Elsevier Science B.V. Keywords: Sample preparation; Vegetables; Food analysis; Pesticides; Carbamates 1. Introduction ticides which cover a wide range of uses in the treatment of seed, soil and crops. Carbamate pesticides have become increasingly The determination of carbamate residues is often important in recent years due to their broad spectrum an intricate problem. Most of the methods developed of biological activity and are used as insecticides, for determination of these compounds are based on a miticides, fungicides, nematocides, and mollus- separation by gas or liquid chromatography [2]. cicides [1]. Among them, the N-methylcarbamate Some of these methods are very sensitive, and have (NMC) insecticides consist of about 15 active com- been adopted by regulatory agencies [3]. Selective pounds that constitute a family of important insec- detection techniques such as fluorescence [3,4] or mass spectrometry [5] minimize the need for clean- up steps because they exclude the co-extractives * Corresponding author co-eluting together with NMCs. Therefore, in most 0021-9673 / 98 / $19.00  1998 Elsevier Science B.V. All rights reserved. PII S0021-9673(97)01176-X