Supercritical fluid extraction coupled with enzyme immunoassay analysis of soil herbicides

Abstract

Supercritical fluid extraction (SFE) was coupled with enzyme immunoassay analysis (EIA) for the analysis of the following herbicides, 2,4-phenoxyacetic acid (2,4-D), 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), 2-chloro-4-ethylamino-6-propylamino-s-triazine (atrazine) and 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor) in soil and compared with liquid vortex extraction (LVE). Five soils, ranging in texture from sandy loam to silty clay were fortified with 500 ng g^–1 of herbicide, allowed to air dry, and extracted using supercritical fluid or LVE. Atrazine and alachlor were also fortified at 50 ng g^–1. Field-weathered soils, with incurred residues from field application, were also extracted. EIA of herbicides using a microtitre plate format were in good agreement with GC and HPLC results (r²= 0.95). SFE was performed using a Dionex (Sunnyvale, CA, USA) Model 703 extractor in the dynamic mode at 20.3 MPa and 66 °C for 3 min, followed by 34.4 MPa extraction for 17 min. SFE recoveries with unmodified CO₂ were 7, 56, 57, and 83%, respectively, for 2,4-D, simazine, atrazine and alachlor. Recoveries improved to 101, 79, 90, and 88% for 2,4-D, simazine, atrazine and alachlor, respectively, by adding 1.5 ml of triethylamine to a 100 ml acetone–water (9 + 1) modifier. Collection of analytes by SFE was improved by using C₁₈ solid-phase traps (90% recovery) compared to liquid acetone collection results (65% recovery).