Anal. Chem. 1994,66, 645-650
Extraction of Atrazine, Cyanazine, Desethylatrazine, Desisopropylatrazine, and Metolachlor from Fortified Western Cornbelt Soils by SFE with COz Thomas R. Stelnhelmer,' Richard L. Pfelffer, and Kenwood D. Scoggln USDA-ARS, National Soil Tilth Laboratory, 2 150 Pammel Drive, Ames, Iowa 500 1 1 Supercritical fluid extraction (SFE) using C02 has been demonstrated as an alternative to polar organic solvents or water for the quantitative removal of atrazine, two of its metabolites, cyanazine, and metolachlor from several agricultural soils. Recoveries of each analyte from soil fortified from 0.1 to 2.0 mg/kg ranged between 25 and 120% depending upon the soil matrix and analyte extracted. A single extraction, using cosolvent-modified C02, conductedat relatively high fluid density in both static and dynamic modes, sufficed for all analytes. Principal component analysis was used to correlate each component in a matrix of dependent variables influencing extraction efficiency. HPLC analysis indicated that fewer coextracted moieties are found using SFE rather than from extractionsusing polar liquid solvents. Addition of both water and methanol to the air-dried soil prior to commencement of C02 flow does enhance the recovery for all analytes. Further, such cosolvents do not promote the conversion of the chlorotriazine analytes to any of their corresponding hydroxy or methoxy analogs under the SFE conditions tested. Atrazine continues to be used for pre- and postemergent control of both grasses and broadleaf weeds in corn, wheat, sorghum, and many other crops throughout the Midwest and the nation. Typical application rates for atrazine on corn have been 2.2-4.4 kg/ha active ingredient, depending upon soil properties, the nature of the crop, atmospheric conditions, and/or type of irrigation program.' In the western corn belt, atrazine is often used in combination with metolachlor or cyanazine to better sustain season-long weed control, especially in fields under conservation tillage practices. Biodegradation of atrazine by soil microorganisms produces, among other products, both desisopropylatrazine and desethylatrazine.2 Soil and water quality studies on the fate and movement of atrazine require analysis of soil for combinations of herbicides, together with their degradation compounds, in order to fully assess their environmental impacts. Supercritical fluid extraction (SFE) emerged as an analytical tool in the m i d - l 9 8 0 ~ . ~SFE - ~ applications in environmental analysis, particularly for heterogeneous solid samples, is emerging as a viable alternative to the more traditional ~
(1) Crop Protection Chemicals Reference, 6th ed.;Chemical and Pharmaceutical Press, John Wiley & Sons, Inc.: New York, 1990; pp 491-512.
(2) Behki, R. M.;Khan,S. U.J.Agric. FoodChem. 1986,34,746-749.Kaufman, D. D.; Kearney, P. C. Residue Rev. 1970, 32,235-265. ( 3 ) Stahl, E.; Schliz, W. Fresenius' 2.Anal. Chem. 1976, 280, 99-104. (4) Stahl, E.; Schilz, W.; Schlitz, E.; Willing, E. Angew. Chem. 1978, 90. 778785. (5) Sugiyama, K.; Saito, M.; Hondo, T.; Senda, M. J. Chromatogr. 1985, 332, 107-1 16. (6) Hawthorne, S.B.; Miller, D. J. J . Chromatogr. Sci. 1986, 24, 258-264. (7) Schantz, M. M.; Chesler, S. N . J . Chromatogr. 1986, 363, 397-401.
This artlcle not subject to U S . Copyright. Published 1994 by the American Chemical Society
methods employing polar liquids or mixtures as extractants. SFE with COa has been used to remove PAHs and heteroatom PAHs, PCBs, PCDDs, and PCDFs from matrices such as highly contaminated soil, river sediment, fly ash, urban particulate matter, and polyurethane foam plugs.8-12 However, most of the successful applications target those contaminants which are hydrophobic, nonpolar, and sparingly soluble in water. Most of these approaches utilize C o t , with or without methanol as modifier, as the fluid; although recoveries for PAHs are reported to be very good using N2O modified with methanoL8 In a comparison to both sonicationand Soxhlet-based methods, C02 with methanol addition was used for the SFE of 16 acid- and base-neutral Priority Pollutants from a Midland County, MI, soil spiked with chlorobenzene and chlorophenol derivatives.13 Most of the analytical applications of SFE to soil-sorbed pesticides have appeared since 1985. Polar organic compounds, including the carboxylicacid herbicides, dicamba and 2,4-D, can be extracted from sand using in situ chemical derivatization under SFE conditions, followed by direct extraction of the chemically modified analytes. However, this technique is very sensitive to matrix effects.14 Sand and a PAH-certified reference soil were used to evaluate extraction efficiency of C02 for 36 nitroaromatics, 19 halogenated diphenyl ethers, and 42 organochlorine insecticide^.^^ Recovery of triazine herbicides from fortified river sediment using C02 with methanol added to the sample matrix has been reported.I6 While none of the degradation products of triazines were included, cyanazine, one of the more difficult triazines to extract and chromatograph efficiently, was successfully recovered over a range of spike concentrations. SFE with methanol-modified C02 was compared with sonication and with Soxhlet extraction of 12 pesticides, 6 chlorinated hydrocarbon and 6 organophosphate insecticides, on four soiltype matrices including clay, sand, topsoil,and river sediment. l7 In this case, SFE was shown to have the best overall precision, (8) Hawthorne, S.B.; Miller, D. J. Anal. Chem. 1987, 59, 1705-1708. (9) Hawthorne, S.B.; Krieger, M. S.; Miller, D. J. Anal. Chem. 1989,61, 736-
740.
(10) Pawliszyn, J.; Alexandrou, N. Anal. Chem. 1989, 61, 2770-2776. (1 1) Onuska, F. I.; Terry, K. A. J . High Resolut. Chromarogr. 1989,12,527-531; 357-361. (12) Langenfcld, J. J.; Hawthorne, S. B.; Miller, D. J.; Pawliszyn, J. Anal. Chem. 1993,65, 338-344. (13) Campbell, R. M.; Richards, M. LC-GC 1991, 9, 358-364. (14) Hawthorne, S. B., Miller, D. J.; Langenfeld, J. J. In Supercritical Fluid Technology; Bright, F. V., McNally, M. P., Eds.; ACS Symposium Series 488; American Chemical Society: Washington, DC, 1992; Chapter 13. (15) Lopez-Avila, V.; Beckert, W. F. In Supcrcrfttcal Fluid Technology; Bright, F. V.,McNally, M. P., Eds.;ACS Symposium Series 488; American Chemical Society: Washington, DC, 1992; Chapter 14. (16)Janda, V.;Steenbeke, G.; Sandra, P. J. Chromatogr. 1989, 479, 200-205.
AnaMIcalChemlshy, Vol. 66, No. 5, M r c h 1, 1994 045
yielding a mean RSD of 90,(**) >95, (***) >99,and (****) >99.9 for n = 127.
of the influence of carbon content on metolachlor recovery approximates that seen for cyanazine even though its water solubility is 3-fold greater. The correlation trend observed for the triazines is analogous to the sorption of atrazine on agricultural soils in which a high correlation is seen between organic carbon content and soil/water distribution coeffi~ i e n t .Independent ~~ confirmation of the importance of soil organic carbon content upon extraction efficiency is seen by recoveries obtained for all atrazine congeners when spiked into the sand matrix. Carbon content of the muffle furnace ignited commercial sand was assumed to be 0
60%
w E
40%
20%
DIA
DEA
CY N
A
MTL
Flgum 3. Results of recovery studies for all analytes for each sdl maMx (mean f standard error of the mean %): Kenyon, 72 f 15%; Ida/Monona,89f 14%;synthetlcsoil,96f ll%;sand,98*8%.
cyanazine, appears to be minimal. For all five compounds, trapping on an ODS sorbent trap appears to offer no significant advantage over stainless steel balls, provided the trap temperature is maintained at least at -5 OC. Chromatograms of SFE extracts reveal fewer coextractants than seen in conventional solvent extractions. Optimal conditions for extraction are dependent on both the analyte and soil matrix. For studies of the assessment of the impact of herbicide usage on soil quality, as well as on surface and groundwater quality, SFE with C02 using polar cosolvent modifiers is a viable alternativeto other extraction methods. Pesticide residues in soil extracts can be chromatographed directly, and concentrations determined by HPLC, without any further cleanup steps.
ACKNOWLEDGMENT We thank Radka Brabkova for preparing the spiked soil samples and Timothy Watts for performing the instrumental work. We are grateful to David Meek for consultation regarding the statistical treatment. Mention of specific products, suppliers, or vendors is for identification purposes only and does not constitute an endorsement by the U.S. Dept. of Agriculture to the exclusion of others. Recehred for review August 20, 1993. Accepted December 7, 1993P Abstract published in Advance ACS Abstracts. January 15, 1994.
