Reversed-phase separation of estuarine interstitial water fractions and the consequences of C₁₈ retention of organic matter

Data are presented on the application of the reversed-phase separation technique for the determination of dissolved organic compounds in estuarine interstitial water. Thirty-seven neutral, nonpolar organic compounds were equilibrated with interstitial water, extracted by emulsion-free gentle liquid-liquid extraction, and quantified using surrogate internal standards. The extraction and quantitation procedures were insensitive to dissolved organic carbon concentration (DOC, 1 to 55 mg C/L). Gross dissolved organic carbon retention by the C₁₈ matrix (7 ± 2%) was similar to the range reported for fresh water; significant regressions of apparent, DOC-normalized, partition coefficients (K′_doc) versus compound solubility and octanol/water partition coefficients (K_ow) were determined. An inverse relationship between K′_doc and DOC concentrations, similar to that reported in fresh water, was found, but was reduced or eliminated for many compounds by accounting for the retained bound compound in the calculation of K′_doc; failure to account for C₁₈ retention of DOM in determining freely dissolved concentrations of high K′_ow organic compounds could result in overestimates of this fraction. Partition coefficients of selected compounds between Aldrich humic acid and distilled water were similar to those found in other studies using radiolabeled compounds.