Abstract: In order to identify matrix effect on the detection of four organophosphorus pesticide residues in cucumber， 3 parallels of acephate， omethoate， methyl parathion and chlorpyrifos were extracted and determined by gas chromatography. All of the four pesticides had matrix effect， and the matrix effect of acephate， omethoate was the highest among them. The matrix effect could be alleviated by calibration of blank with standard substances. Moreover， the adsorption on inject port could result in errors. The determination of 3 parallels of omethoate increased and deviated from theoretical value. The matrix effect on omethoate determination could be effectively eliminated by calibration of blank with standard substances and taking average value.

Key words: matrix effect, gas chromatography, pesticide residue, organophosphorus