CLEANUP AND CONFIRMATORY PROCEDURES FOR GAS-CHROMATOGRAPHIC ANALYSIS OF PESTICIDE-RESIDUES .2.

The behaviour of standard solutions of fourteen simple organohalogenated pesticides, nine individual polychlorinated biphenyls (PCBs) and Aroclor 1242, 1248, 1254 and 1260 on treatment with sulphuric acid, potassium hydroxide and chromium(IV) oxide was studied by capillary gas-liquid chromatography (cGC) using electron-capture detection. These methods were applied to confirm the presence of organochlorine residues in river water and human milk. Positive confirmation with the three treatments were in agreement with capillary GC(cGC)-MS determinations carried out in the electron impact and selected-ion monitoring mode. After cGC analyses, the extracts containing possible pesticides or Aroclors were treated with the three chemicals and re-analysed under the same cGC conditions. The new chromatographic profiles showed many missing artifact peaks, and some pesticides or PCBs were also destroyed. The presence or disappearance of the peaks after chemical attack makes it possible to identify the specific pesticides and PCBs analysed. PCBs resist both acid and alkali attacks, but some low-chloride PCBs are totally or partially destroyed by oxidative treatment. The methods studied are useful for intralaboratory purification and confirmation of residues of pesticides and PCBs, although they can be insufficient for identifying organochlorine pesticide residues from some very polluted samples.