Solid-phase microextraction method for the determination of atrazine and four organophosphorus pesticides in soil samples by gas chromatography

A simple and rapid solid-phase microextraction (SPME) based method is presented for the simultaneous determination of atrazine and four organophosphorus (i.e. parathion-methyl, chlorpyriphos, methidathion and carbophenothion) in soils. After optimisation of the different experimental variables affecting the SPME of the target compounds from aqueous solutions by using an experimental design, a consensus strategy was adopted which allowed the use of the SPME method developed for the simultaneous screening of all the analytes selected. The complete analytical procedure finally proposed consisted of a 15-min ultrasonic extraction of the target compounds from a 0.5-g soil sample with 5 ml of methanol and the dilution of this extract to up 10% methanol followed by the addition of NaCl to a final concentration of 10% (w/v). The analytes in this aqueous extract were preconcentrated for 30 min in the SPME fiber and subsequently desorbed by heating of the fiber at 260°C for 5 min in the gas chromatograph injection port. Final determination was carried out with an electron-capture detector. The recoveries of the pesticides studied in soils ranged from 72 to 123%, except for atrazine, and the SDs were below 16%. The feasibility of the procedure finally proposed for the screening of the endogenous pesticides irrespective of the properties of the soil selected has been shown.