Application of activated carbon membranes for on-line cleanup of vegetable and fruit extracts in the determination of pesticide multiresidues by gas chromatography with mass selective detection

The feasibility of using activated carbon membranes for the on-line cleanup of vegetables and fruits samples in the determination of pesticide multi-residues was investigated. The interactions of over one hundred pesticides, including organochlorine, organophosphorus and organonitrogen compounds, in various solvents and vegetable and fruit extracts with the activated carbon membranes were studied. It was found that in general pesticides containing benzene rings with small substituents interacted strongly with the carbon membranes when the pesticides were dissolved in acetone, acetonitrile or ethyl acetate. On the other hand, pesticides without benzene rings or with benzene rings containing bulky substituents showed little or no interaction with the carbon membranes when dissolved in the above mentioned solvents. Addition of toluene to solutions of pesticides in either acetone or acetonitrile was necessary to minimize these interactions. A simple cleanup procedure for fruits and vegetables, involving the filtering of a sample slurry in 25% toluene in acetonitrile through an activated carbon membrane, followed by concentration and injection into a gas chromatograph equipped with a mass selective detector was developed. Recovery data from spiked lettuce, green pepper, pear and lemon are presented as well as data from real samples. With a few exceptions, over one hundred pesticides were quantitatively (>80%) recovered using the novel procedure.