Multivariate optimization of the factors influencing the solid-phase microextraction of pyrethroid pesticides in water

A method based on solid-phase microextraction (SPME) and gas chromatography with micro-electron capture detection (GC-μECD) has been optimized for the analysis of pyrethroids in water samples. The influence of parameters such as temperature, fibre coating, salting-out effect and sampling mode on the extraction efficiency has been studied by means of a mix-level factorial design, which allowed the study of main effects as well as two factor interactions. Finally, a method based on direct SPME at 50 °C, using polydimethylsiloxane fibre is proposed. The method showed good linearity (R2 > 0.995) and repeatability (RSD ≤ 16%) for all compounds, with detection limits ranging from 0.05 pg/mL for transfluthrin to 2.18 pg/mL for permethrin, and in general ≤1 pg/mL for most pyrethroids. Reliability was demonstrated through the evaluation of the recoveries in different water samples, such as tap water, groundwater, river water, runoff water, and wastewater. These studies demonstrated the validity of external standard calibration to quantify the target compounds in real samples, including a simple dilution step for the most complex matrices, which notoriously simplifies quantification by SPME.