Application of graphitized carbon black to the QuEChERS method for pesticide multiresidue analysis in spinach

A modified QuEChERS method was optimized to determine 66 pesticide residues in spinach using gas chromatography with mass spectrometric detection in selected-ion monitoring mode. Graphitized carbon black (GCB) at different levels (0, 5, 10, 15, 20, and 25 mg) was used to adsorb the pigments in spinach extracts. Best recoveries with less colored extract samples for all pesticides analyzed were obtained in the presence of 10 mg GCB. Under the optimized condition, analyses of spiked samples were performed at 3 different levels. Correlation coefficients, R2, in the linear range tests were better than 0.99. Average recoveries ranged from 66 to 104%, with the relative standard deviation below 16%. The limits of quantitation ranged from 50 to 250 microg/kg.