Pesticide analysis in herbal infusions by solid-phase microextraction and gas chromatography with atomic emission detection

A direct immersion solid-phase microextraction (SPME) procedure was used in combination with capillary gas chromatography with atomic emission detection (GC-AED) for the determination of 10 pesticides (organochlorines, organophosphorus compounds and pyrethrins) in herbal and tea infusions. Ionic strength, sample dilution and time and temperature of the absorption and desorption stages were some of the parameters investigated in order to select the optimum conditions for SPME with a 100 μm PDMS fiber-coating. Element-specific detection and quantification was carried out by monitoring the chlorine (479 nm) and bromine (478 nm) emission lines, which provided nearly specific chromatograms. Calibration was carried out by using a spiked sample infusion. The detection limits varied between 11.9 ng ml⁻¹ for deltamethrin and 0.03 ng ml⁻¹ for p,p′-DDE and p,p′-DDD. The recoveries ranged from 73.5% for deltamethrin to 108.3% for p,p′-DDT in a spiked white tea infusion. Two of the eight samples analyzed contained low levels of some the pesticides considered.