22. Sample handling and determination of carbamate pesticides and their transformation products in various matrices

Abstract

Abstract The use of non-persistent carbamate pesticides, which often replace organochlorine and organophosphorus compounds, is increasing because of their broad spectrum of activity, high pesticide effectiveness and generally low mammalian toxicity. Suitable analytical procedures for the determination of these pesticides in a variety of environmental matrices are therefore required. Analysis of the degradation products of the carbamates is also of interest, since their toxicity may be higher than that of the parent compounds. A large variety of carbamates is currently in use. Their application as an insecticide, fungicide or herbicide is related to the molecular structure. The insecticides have the N-substituted carbamate moiety and, generally, an aromatic ester or an oxime function. The fungicides have either a benzimidazolyl ester, a pyrimidyl ester or a (bis)dithiocarbamate group. The herbicides have an N-alkylthiocarbamate or an N-phenyl carbamate group [1–3]. Figure 1 shows a general representation of these subclasses. The degradation products are generally oxidized derivatives, e.g. aldicarb sulphone (from aldicarb), or alcohols formed by saponification of the carbamic acid group, e.g. 1-naphthol (from carbaryl). The general degradation pathways of carbamate pesticides were discussed by Schlagbauer and Schlagbauer [4], while several reports deal with fate studies of specific carbamates: aryl N-methylcarbamates [5,6], benomyl [7,9] and oxime N-methylcarbamates [10,14]. The biodegradation of some carbamates in various environmental matrices has also been studied [15]. Many analytical methods have been developed for the determination of the carbamate pesticides. In addition to the currently most common analytical techniques such as gas chromatography (GC), liquid chromatography (LC), and supercritical fluid chromatography (SFC), other methods, e.g. bioassays [16], stopped flow Chromatographie techniques [17], thin layer chromatography [18] and colorimetry [19–21] have been employed. This chapter will focus on GC-, LC and SFC based analytical methods. The rapid growth of the use of carbamate pesticides over the last two decades requires that validated analytical procedures be developed. It should be possible to determine low concentration levels down to e.g. 0.1 g.l 1 for drinking water [16]. Furthermore, multiresidue analytical procedures, which comprise the carbamates and their transformation products, are of much current interest, because their use effectively reduces analysis time an expense. Amongst other, our group, with the support of the Community Bureau of Reference (BCR, Measurements and Testing Programme, Brussels) of the European Commission, has developed validated extraction, clean-up and analytical methods for the determination of carbamate (and some other) pesticides in different environmental matrices. So far, several review papers concerning the use of LC [22–24] and mass spectrometry (MS) [25] have been published. In the following, procedures for LC, GC and SFC analysis of some subclasses of carbamates (and their degradation products) in various matrices will be discussed. The chapter, divided into three sections, covers: (1) sample preparation from water, plant materials and soil, (2) LC, GC and SFC separations and (3) ultraviolet (UV), fluorescence, electrochemical (ECD) and mass spectrometric (MS) detection in LC.