Matrix-induced effects:: a critical point in the gas chromatographic analysis of pesticide residues

The influence of several experimental factors related to the enhanced gas chromatographic responses yielding apparent recoveries of pesticide residues greater than 100% was investigated. Optimisation of a gel permeation chromatographic clean-up step with respect to the trueness and precision of generated data was performed. An increase of relative detector response (100%=response of analyte in pure solvent solution) was evidenced to be dependent both on the concentration of the analyte and the character of the matrix: pronounced matrix-induced effects were observed particularly in orange and wheat extracts at low concentration levels of analytes (especially for GC-electron-capture detection analysis of certain pesticides). As soon as the splitless injector became contaminated after injection of large series of matrix-containing samples, a decrease of relative responses of pesticides, largely below 100%, was experienced. Although troublesome compounds tending to give matrix-induced effects can be identified, and increased recoveries may he tentatively predicted, poor accuracy of generated data can be presumed as long as quantitation is not based on a standard prepared in blank matrix extract to compensate for matrix-induced effects. (C) 1998 Elsevier Science B.V.