Three different peptides (His-Glu-Pro-Ser, His-Gly-Ser-Ala and Glu-Pro-Ser-Ala) were selected and tested to be used as affinity binding receptors for organophosphate and carbamate pesticides. The peptides were rationally designed by mimicking acetylcholinesterase active site. The simulated binding energy of the three tetrapeptides versus one model of organophosphate (paraoxon) and one of carbamate (carbaryl) pesticide was calculated; a good correlation between shape designed and binding score was obtained. The binding properties of the peptide-pesticide interaction were studied following the variation of UV-visible spectra in different solvents. The binding constants in water, which were nicely correlated with computational data, ranged from 506 (+/-115) to 36(+/-2) M(-1). All the peptides had a 5-fold decrease in binding by changing solvent, going from water to less polar ethanol. The binding affinity suggested the use of these ligands as a preanalytical tool in extraction cartridges. The tetrapeptides efficiency was tested linking the peptides to two different supports. The cartridges prepared using His-Glu-Pro-Ser sequence was, as predicted, able to bind paraoxon and carbaryl with recovery values in the 72-88% range at pH 4.5. Intercolumn, interday RSD was in the 4-7% range. The columns were used for 80 cycles before losing retention ability.