DETERMINATION OF RESIDUES OF PHENOXY ACID HERBICIDES IN SOIL AND CEREALS BY GAS-CHROMATOGRAPHY ION-TRAP DETECTION

The analysis of several phenoxy acids in soil and cereals was carried out by gas chromatography with ion trap detection, after derivatization with BF3-methanol. Soil was extracted with methylene chloride, at acidic pH, on an orbit shaker, and plants were extracted with a 0.1 M NaOH solution in a Sorvall homogenizer. The extracts were cleaned up by liquid-liquid partition, the organic solvents evaporated and residues methylated. Herbicides residues were determined by gas chromatography-ion trap detection on a BP-1 capillary column with helium as carrier gas. Recovery through the method was studied in the range of 0.2 to 2 mu g/g and was found higher than 80% for each herbicide in both matrixes. Residues of phenoxy acids were determined by selecting the base peak of their spectra, after acquisition of the total-ion chromatogram of the sample. The limit of detection in the selected-ion mode was 0.005 mu g/g in soil and 0.04 mu g/g in plant samples.