Comparison of sorbents using semipolar to highly hydrophilic compounds for a sequential solid-phase extraction procedure of industrial wastewaters

Untreated and biologically cleaned industrial wastewaters contain huge amounts of both hydrophilic and hydrophobic compounds. Due to breakthrough effects, only a few percent of the dissolved organic carbon is usually extracted by solid-phase extraction methods. Methods for screening analysis have not faced that problem sufficiently yet. To extract more hydrophilic compounds, solid-phase sorbent characteristics had to be evaluated in this study. Recovery studies were carried out with 21 hydrophilic aromatics including carboxy acids, sulfonates, aldehydes, ketones, thiols, and phenols at a level of 1-2 mu mol/L. Both silica gel based sorbents and polymeric materials were tested at neutral to acidic pH values and extraction volumes up to 200 mL. It was found that poly(styrene-divinylbenzene) sorbents are a powerful tool for the enrichment of hydrophilic aromatic substances, Most of the tested compounds could be extracted at recovery rates of >80%. The quantitative extraction of thiols as well as (aminohydroxy)disulfonic acids remains an unsolved problem. Finally, combination of different solid sorbents and pH changes is suggested for sequential extraction of heavily loaded industrial wastewaters, Advantages and limitations are discussed and an example of its usefulness is given.