Multiresidue herbicide analysis in soil: Subcritical water extraction withan on-line sorbent trap

We evaluated the feasibility of extracting selectively and rapidly herbicid e residues in soils by hot water and collecting analytes with a Carbograph 4 solid-phase extraction (SPE) cartridge set on-line with the extraction ce ll. Phenoxy acid herbicides and those nonacidic and acidic herbicides which are often used in combination with phenoxy acids were selected for this st udy. Five different soil samples were fortified with target compounds at le vels of 100 and 10 ng/g (30 ng/g of clopyralid and picloram) by following a procedure able to mimic weathered soils. Herbicides were extracted with wa ter at 90 degrees C and collected on-line by the SPE cartridge. After the c artridge was disconnected from the extraction ap-l paratus, analytes were r ecovered by stepwise elution to separate nonacidic herbicides from acidic o nes. The two final extracts were analyzed by liquid chromatography/ mass sp ectrometry with an electrospray ion source. At the lowest spike level consi dered, analyte recoveries ranged between 81 and 93%, except those for 2,4-D B and MCPB, which were 63%. For 16 herbicides out of 18, the ANOVA test sho wed recoveries were not dependent on the type of soil. The method detection limit was in the 1.7-10 ng/g range. For the analytes considered, method co mparison showed this extraction method was overall more efficient than Soxh let and sonication extraction techniques.