Determination of Imazethapyr Using Capillary Column Flow Injection Liposome Immunoanalysis

A sensitive immunoanalysis system was developed for the quantitation of imazethapyr, the active ingredient in PURSUIT herbicide. Imazethapyr [5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid] is one of the imidazolinone class of herbicides. The assay was based on sequential competitive binding of imazethapyr and liposomes for a limited number of antibody binding sites. A capillary tube (20 cm × 0.53 mm i.d.) with immobilized antibody was used as the immunoreactor column. Liposomes that entrap fluorescent molecules as the detectable label provide instantaneous, rather than time-dependent, enhancement, common with enzyme immunoassays. In this study, liposomes encapsulated carboxyfluorescein dye and were made antigenic by incorporating in the bilayer a phospholipid that had the analyte conjugated to its polar head group. The calibration curve for imazethapyr in Tris-buffered saline solution had a working range of 0.1−100 ng/mL. In the range between 1 and 100 ng/mL, recoveries from fortified tap and pond water samples ranged from 93 to 114%. Filtration was the only step needed for sample cleanup, and an assay could be performed in <10 min.