Abstract: The principles of flow injection - renewable surface techniques are presented. The technique uses polymer particles, such as those used in chromatography, as reagent carriers. A small amount of the polymer was injected into the carrier stream and deposited in a jet-ring cell prior to injection of the analyte. Two examples of this technique ware described, namely: (i) the competitive immunoassay of the herbicide imazethepyr with fluorimetric detection; and (ii) the determination of Cr(VI) with reflectance spectrophotometric detection. For (i) imazethepyr competes with fluorescein-labelled imazethepyr for antimidazine mAb attached to Protein A conjugated beads. The calibration range was 5-5000 ng/ml and the RSD was 5% at the 2500 ng/ml level. For (ii) the reagent 1,5-diphenylcarbazide was adsorbed on to Polysorb C-18 beads. The calibration graph for Cr(VI) was linear for 10^-200 ng/ml at 540 nm and with a 500 µL injection volume.

Abstract: Imazethapyr is the herbicide developed for use in leguminous crops. In this study, flow-injection liposome immunoanalysis (FILIA) has been shown to be capable of measuring imazethapyr in a buffered solution with a detection limit of 0.1 ppb through the optimization process. Protein A coated glass beads covalently conjugated with antibody were contained in a glass column, and this column was used as an immunoreactor. Liposomes which encapsulated a fluorescent dye, sulforhodamine B (SRB) or carboxyfluorescein (CF), generated the analytical signal. By loading larger volumes of sample onto the column, it was shown that the detection limit could be lowered. Liposomes containing carboxyfluorescein gave more sensitive response and a lower detection limit than those with sulforhodamine B. Also, improved response was obtained by using a smaller flow cell in the fluorescence detector due to the reduced dilution effect.

Abstract: 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 x 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.