Interpretation of Sorption Studies for Compound Isomers or Mixtures

For compound mixtures or compounds with two or more differently sorbing isomers which are not analytically distinguished, combined sorption parameters determined in the laboratory are dependent upon the ratio of different compounds or isomers and upon experimental methods and conditions. The purpose of this paper is to mathematically examine the effects of these factors on sorption parameters calculated from batch (shake‐flask) and continuous flow column sorption studies of compound or isomer mixtures. The analysis in this paper helps explain the apparent anomalies between batch and column sorption results in previously published studies of Rhodamine WT (RWT). In batch reactors, the solid: liquid ratio, R s , has a major effect on batch sorption results. As R s decreases, partitioning coefficients determined from batch results approach those determined from column results, which is contrary to the trend that may be anticipated for single component analytes. A single column sorption coefficient or retardation factor for multiple constituents does not accurately describe the transport of the individual compounds. The implications of the effects of experimental methods suggest that sorption parameters determined from batch studies for compound or isomer mixtures (e.g., BTEX, combined xylenes, and others) should be interpreted with care. Significant errors in prediction and description of contaminant transport can result if the presence of multiple compounds or isomers is not recognized or if batch or column data for compound or isomer mixtures are misinterpreted.