The gas chromatographic flame photometric detector (FPD)-phosphorus mode response to organophosphorus (OP) pesticides was studied for the following solvents: acetone, isooctane, acetone-isooctane (1 + 9), methanol and ethyl acetate. Both single and dual FPDs were used. Some OP pesticides yielded significant differences in FPD response when the various solvents were used. For example, the response to 6.7 ng monocrotophos (azodrin) was 0.37 in isooctane relative to the same amount of monocrotophos in acetone, using a dual flame detector. Because the FPD response to OP pesticides is dependent on the solvent used, OP standard solutions for quantitation of pesticide residues should be prepared in a solvent nearly identical to the solvent in the sample solution.
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