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Development of a Solid Phase Extraction Method for Agricultural Pesticides in Large-Volume Water Samples
Citation:
MOMPLAISIR, G., C. G. ROSAL, E. M. HEITHMAR, K. E. VARNER, L. A. RIDDICK, D. F. BRADFORD, AND N. G. TALLENT-HALSELL. Development of a Solid Phase Extraction Method for Agricultural Pesticides in Large-Volume Water Samples. Journal of Separation Science. Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, 81:1380-1386, (2010).
Impact/Purpose:
Methods with well established performance are available for the determination of pesticides in fresh water at ng/L levels. They often involve solid phase extraction (SPE) of about 1 L of water, followed by GC/MS with selected ion monitoring (SIM) [1, 2]. Recently, advanced materials for SPE extraction have been investigated with separation by liquid chromatography and ultraviolet absorption detection (HPLC/UV). Al-Degs and Al-Ghouti extracted water with multiwall carbon nanotubes [3]. Fontanals et al. used monodisperse, hypercrosslinked microspheres for extraction [4]. Over the past decade, interest has grown in the occurrence and distribution of pesticides and other organic pollutants in less impacted environmental waters, such as rainwater [5], snow and ice cores [6], and remote surface water bodies [7-9]. This interest has driven the development of more sensitive analysis methods, generally using one of three general approaches: improving sensitivity and selectivity of the determinative instrumental method, increasing the fraction of extracted pesticide that is analyzed, or increasing the total volume of water extracted. Selectivity of GC/MS for pesticides with high electron affinities can be enhanced by using negative chemical ionization (NCI), rather than the more common electron ionization (EI). McConnell et al. used GC/NCIMS to determine 10 organochlorine pesticides in rainwater and snow melt with 20-500 pg absolute detection limits [10]. Selectivity with either NCI or EI can be improved by the use of tandem mass spectrometry. Pitarch et al. used this approach to analyze C18 extracts of 100 mL of water for 25 pesticides, and achieved detection limits of 200 pg/L of hexachlorobenzene by NCI [11].
Description:
An analytical method using solid phase extraction (SPE) and analysis by gas chromatography/mass spectrometry (GC/MS) was developed for the trace determination of a variety of agricultural pesticides and selected transformation products in large-volume high-elevation lake water samples. The targeted compounds comprise pesticides (and selected oxygen transformation products) known to have been extensively used in agriculture in the San Joaquin Valley, California, USA. The method was developed to evaluate air transport of these compounds to high elevation lakes in the southern Sierra Nevada mountains thus, low limits of detection were a primary method performance objective. Solid phase extraction using the polymeric resin Abselut Nexus was optimized to extract the pesticide analytes from water samples up to 100 L. A single determinative method using GC/MS with electron ionization was used for all analytes. The method evaluation demonstrated acceptable performance for 39 of the 44 targeted analytes. Recoveries from 100 L of reagent water at 100 pg/L and 1 ng/L concentrations were generally greater than 75%. Analysis of the extracts without cleanup yielded detection limits generally below 500 pg/L. A silica cleanup with separate analysis of three eluent fractions reduced detection limits for 35 compounds to between 2 and 70 pg/L.