Influence of Ethanol on Pesticide Extraction in Aqueous Solutions by Solid-Phase Microextraction

The new extraction method, so-called solid-phase microextraction (SPME), coupled with gas chromatography-mass spectroscopy (GC-MS), was examined for the determination of residues of insecticides and fungicides commonly used for vineyard protection. Aqueous solutions containing between 0 and 15% ethanol were spiked with 12 selected compounds and diphenylamine at the level of 20 ppb (v/w), extracted onto a silica fiber coated with a 100-μm thickness of poly(dimethylsiloxane), and desorbed in the chromatograph injector. The influence of ethanol on the partition equilibrium between the adsorbant and the liquid was studied for each product. In several cases, equilibria were obtained, and the extracted amounts of pesticides were shown to be dependent on the nature of the molecule and on the ethanolic content of the solution. In contrast, the time necessary to reach these equilibria was the same in the presence and absence of ethanol. Additional experiments on natural wines spiked at the same level of concentration were analyzed under the same conditions, and the results were compared with those obtained from reference solutions.