Helena Prosen, Andreja Troha, Lucija Zupančič-Kralj
Faculty of Chemistry and Chemical Technology, Aškerčeva 5, SI-1000 Ljubljana, Slovenia
The interaction of three organochlorine insecticides lindane, heptachlor and dieldrin with humic acid (HA) was studied in water suspension by means of gas chromatographic analysis with electron capture detection (GC/ECD) and solid-phase microextraction (SPME). The use of internal standard ?-endosulfan to improve repeatability was abandoned as it was also bound to HA. Pesticides were quantified by external standards. SPME-GC/ECD method was linear in the 0.5 - 20.0 ?gL-1 concentration range with RSD below 10%. Up to 90% of organochlorines was bound to humic acids at contact time of 35 days. Equilibrium between free and bound fraction of pesticides was reached after 10 - 15 days and was not affected by pH, ionic strength or concentration of humic acid in suspension, suggesting the purely hydrophobic interaction between pesticides studied and humic acid. SPME was compared to solvent extraction to test its applicability in HA suspensions. The results for both extraction methods were similar except for lindane because of a coeluting compound arising from degradation of humic acid.