EXPLANATION OF THE MATRIX-INDUCED CHROMATOGRAPHIC RESPONSE ENHANCEMENT OF ORGANOPHOSPHORUS PESTICIDES DURING OPEN-TUBULAR COLUMN GAS-CHROMATOGRAPHY WITH SPLITLESS OR HOT ON-COLUMN INJECTION AND FLAME PHOTOMETRIC DETECTION

The observed chromatographic response for organophosphorus pesticides in extracts from milk and butterfat is shown to matrix dependent. The matrix protects the organophosphorus compounds from adsorption and/or decomposition in hot vaporizing injectors ensuring a more complete tra nsfer from injector to column compared to the results observed when st andards dissolved in matrix-free solvent are used. This results in rec overies in excess of 100% for residue-free extracts spiked with organo phosphorus pesticides when standards prepared in residue-free solvents are used for calibration. The chromatographic response enhancement is minimized by using hot on-column injection at an optimized injection temperature, but not completely eliminated. The preferred method of ca libration is to use matrix standard solutions prepared by adding known amounts of organophosphorus pesticides to residue-free sample matrix of the same character and in similar concentration to the samples to b e analyzed.