Subcritical (hot) water/ethanol extraction of nonylphenol polyethoxy carboxylates from industrial and municipal sludges

Subcritical (hot) water with ethanol as modifier was used to extract nonylphenol polyethoxy carboxylates (NPECs) with 1-4 ethoxy groups from sludge samples. Quantitative recovery of native NPECs from sludge was accomplished by extracting 0.25 g samples for 20 min with 30% (v/v) ethanol in water at 75 degrees C and 150 bar. NPECs in the water/ ethanol extract were concentrated by a strong anion exchange (SAX) Empore disk. The NPECs were simultaneously eluted and derivatized to their methyl esters in an autosampler vial. Although carbon dioxide, hot water, and methanol-modified hot water were evaluated for NPEC recovery, ethanol-modified hot water yielded the highest recovery of native (unspiked) NPEC from sludge. Samples analyzed for this study included an anaerobically-digested municipal sludge, a commercial product containing anaerobically-digested municipal sludge and yard waste, and secondary clarifier sludge obtained from a paper mill. NPEC concentrations ranged from 27 to 113 mu g/g with NP2EC as the most abundant oligomer. Samples of anaerobically-digested sludge had ortho-to-para isomer ratios greater than or equal to 1, which indicated the depletion of para NPEC isomers relative to ortho isomers during anaerobic sludge treatment. In contrast, secondary clarifier sludge from a paper mill that had not undergone anaerobic treatment contained only para NPEC isomers.