Analysis of pesticide residues by on-line reversed-phase liquid chromatography-gas chromatography in the oil from olives grown in an experimental plot

This paper describes the use of a fully automated on-line reversed-phase liquid chromatography-gas chromatography (RPLC-GC) method for the determination of four organophosphorus pesticides (dimethoate, methidathion, chlorpyriphos and fenitrothion) in olive oil. These pesticides are among those more extensively used to control pests and disease in olive trees. Various treatments with these pesticides, at various doses and stages of olive ripening, were carried out in an olive grove. The olives were harvested in mid-December and immediately processed into oil in the laboratory. Fully automated analyses by on-line RPLC-GC using the through oven transfer adsorption desorption (TOTAD) interface was carried out without any kind of sample pretreatment other than a simple filtration step. A statistical analysis was performed. No dimethoate remained in the oil owing to the high solubility of dimethoate in water. Differences between the other three pesticide residues were significant. Chlorpyriphos provided the lowest residues, followed by fenitrothion and methidathion. Treatments carried out in June did not leave residues in the oil, but all the treatments carried out in October and December led to pesticide residues that were higher than the limits of detection.