2. Experimental
2.1. Chemicals and reagents
Pesticide analytical standards were purchased from Dr.
Ehrenstorfer (Ausburg, Germany). Chemical structures for
the pesticides studied in this work are shownin Fig. 1. Individual
pesticide stock solution (200–300 g/ml) were prepared
in pure methanol and stored at−18 ◦C. HPLC-grade acetonitrile
and methanol were obtained from Merck (Darmstadt,
Germany).AMilli-Q-Plus ultra-purewater system from Millipore
(Milford, MA, USA) was used throughout the study
to obtain the HPLC-grade water used during the analyses.
Formic acid was obtained from Fluka. Pesticide-grade ethyl
acetate and anhydrous sodium sulphate were from Panreac
(Barcelona, Spain).