Optimization of solid-phase extraction procedure for determination of polychlorinated dibenzo- p-dioxins,...

A solid-phase extraction (SPE) method was optimized for accurate determination of polychlorinated dibenzo- p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (CoPCBs) in humic acid containing surface water. Recovery experiments using humic materials revealed that humic acids permit dioxins to pass through an octadecylsilica (C(18)) extraction disk by associating with them under weakly alkaline conditions. Acidification of the sample before percolation improved this otherwise insufficient recovery. The analysis of surface water acidified to pH 2 gave better recovery with surrogate standards and lower quantitative values for higher-chlorinated homologues than the sample at pH 9. In all samples, the native octachlorodibenzo- p-dioxin (OCDD) peak abundance showed no difference between at pH 2 and at pH 9, indicating overestimation of the quantitative value of the homologue at pH 9. Acidification of a humic acid containing water sample can avoid overestimation of higher-chlorinated congeners caused by insufficient recovery of their corresponding surrogates.