DETERMINATION OF CAPTAN IN WATER, PEACHES, AND APPLE JUICE BY A MAGNETIC PARTICLE-BASED IMMUNOASSAY

A magnetic particle-based enzyme-linked immunosorbent assay (ELISA) wa s used to determine captan residues in water, peaches, and apple juice . Precision studies of captan-spiked water samples showed coefficients of variation (CVs) of 24% at 0.1 ppm and 15% at 2.0 ppm. Average reco veries from water were 110-118%, with an estimated sensitivity of 0.01 ppm for captan. tow cross-reactivity was seen with the related phthal imide fungicides captafol and folpet. A least-detectable dose (LDD) of 1 ppm was estimated for captafol in the immunoassay; an LDD of 8.6 pp m was estimated for folpet. Apple juice samples were analyzed by a 3-s tep procedure: the sample was concentrated on a Cls bonded silica soli d-phase column, the eluate was diluted in buffer, and the sample was a ssayed by ELISA. The detection limit in apple juice was estimated to b e 0.1 ppm on the basis of the detection limit observed in water and th e required calculation factors; the average recovery was 115%. Acetone extraction, C rs bonded silica solid-phase extraction column, and the immunoassay were used consecutively to analyze peach samples. The det ection limit in peaches was estimated to be 0.15 ppm on the basis of t he detection limit observed in water and the required calculation fact ors. Captan residues were found in all but one of the peach samples an d ranged from 0.15 to 1.12 ppm (mu g/g). Recovery of added captan from peaches averaged 98% for both spike levels tested. Results of analysi s of captan in peaches by immunoassay and gas chromatography with elec tron capture detection (GC/ECD)were compared. GC/ECD gave an average r ecovery of 75%; immunoassay gave an average recovery of 112%.