Solid phase microextraction (SPME) can be applied to measure the distribution of chemicals in different speciation states. The standard SPME apparatus and procedures can be applied to measure free concentrations of a target compound spiked into pure water and spiked into water containing another pseudophase, such as dissolved humic organic matter (HOM). Based on a comparison of results obtained for the two samples, the partitioning of the target analyte between water and the pseudophase is calculated. The samples investigated in the present study were from heavily contaminated coal wastewater containing dissolved organic polymers with properties similar to those of HOM. External calibration provides information about freely dissolved analytes. After calibration of the SPME signal by addition of an internal standard (e.g., a deuterated surrogate), the results indicate the total concentration of the target analyte in the sample due to the identical partitioning of the internal standard. The concentration determined in this way coincides well with data obtained from liquid−liquid extraction (LLE). Both methods, SPME with internal calibration and LLE, measure total concentration, composed of a freely dissolved portion and a portion that is reversibly bound onto a pseudophase (HOM).