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RAPID PESTICIDE EXTRACTION AND ANALYSIS METHODS FOR BETTER ...
RAPID PESTICIDE EXTRACTION AND ANALYSIS METHODS FOR BETTER ENVIRONMENTAL MANAGEMENT OLIVER, G; DOYLE, R; JORDAN, T; BROWN P Tasmanian Institute of Agricultural Research, Private Bag 54, University of Tasmania, Hobart, TAS 7001, Australia. Garth.Oliver@utas.edu.au ABSTRACT Public concerns expressed by the Tasmanian shell fish industry and medical practitioners regarding pesticide use required validation of a best practise pesticide model for local conditions. The collection of data to validate the model PIRI (Pesticide Impact Rating Index; Kookana and Correll, 2008) involved the processing of large numbers of soil samples over a very short project timeframe. Samples from field and laboratory trials needed to be collected, stored, processed, extracted and then analysed. The logistics of dealing with several thousand samples through all these stages requires careful planing and automation. Of particular importance is the preparation, extraction and clean-up of soil extracts prior to analysis. The pesticides cypermethrin, clopyralid, glyphosate, MCPA, simazine and sulfometuron methyl were applied to five different Tasmanian soil types to determine their field half-lives and leaching potential. Sorption coefficients for the five soils were also required for PIRI. Four different extraction protocols were required to deal with this broad suite of pesticides highlighted by the community consultative committee. An accelerated solvent extraction system (Dionex ASE 200) interfaced with an automatic liquid handling system (Gilson ASPEC XL) was chosen for five of the pesticides. ASE allows for the automated extraction of twenty four 1-10 g soil samples by common laboratory solvents at elevated temperature and pressure. The extracts can subsequentially be concentrated or cleaned via Solid Phase Extraction (SPE) methods performed automatically by the ASPEC XL system. Extraction of MCPA, simazine and sulfometuron methyl were combined in a single extraction cell then filtered using a 0.45 micron filter and then analysed by LCMS-MS. However clopyralid required separate extraction, clean-up and analysis due low detector sensitivity and poor chromatography. The ASPEC system was used to automatically pre-condition a 3 g GCB cartridge which was dried and then eluted before analysis by LCMS-MS. Aqueous insolubility with cypermethrin meant it was also extracted separately in ASE cells, cleaned-up and run on a GCMS-MS. Glyphosate extraction was trialled with both 0.1M and 0.01M KOH, adjusted to pH 2 by orthophosphoric acid, and then analysed by HPLC using fluorescence detection. The weaker extraction solvent (0.01 M KOH) was trialled due to reduced matrix interference. However on certain soils the extraction efficiency was compromised and the stronger extraction solvent was needed (see Figure 1). Figure 1 shows the differences in extraction efficiency of the two different KOH concentrations on the five soil types seven days after glyphosate application. No glyphosate was detected in the northern Red Ferrosol extract. This is a soil with high levels of iron oxides and is strongly P sorbing. Both these factors are linked to glyphosate sorption (Vencill, 2002) and suggest KOH extraction(s) maybe inappropriate in some soils. Conversely the sandy textured Kurosol showed little variation in extraction efficiency. Glyphosate extration efficency 3.00 0.01M KOH 2.50 mg/kg in Soil 0.1M KOH 2.00 1.50 1.00 0.50 0.00 th h ol ol ol St N s os s ro rto ol ol m Ku Ve s s er rro rro D Fe Fe Soil Type Figure 1 Extraction of glyphosate using either 0.1 M or 0.01 M KOH seven days following application to a range of Tasmanian soils. The ASE/ASPEC system allowed for constant unsupervised extractions that maximised sample throughput. These developments mean large and accurate data sets can be generated rapidly for better modelling of pesticide behaviour which are locally relevant and utilised by various community and industry groups. References Kookana, R. and Correll, R. 2008, Pesticide Impact Rating Index (PIRI) risk indicator for minimizing off-site migration of pesticides. Tasmanian Water Quality Initiative, CSIRO Land and Water, Adelaide, Australia. Vencill, W.K. 2002, Herbicide Handbook, 8th Edition, Weed Science Society of America, 493p.
"RAPID PESTICIDE EXTRACTION AND ANALYSIS METHODS FOR BETTER "