Quality Control Associated with use of Semipermeable Membrane Devices

Semipermeable membrane devices (SPMDs) were used to monitor polycyclic aromatic hydrocarbons (PAHs) in an urban stream. Replicate SPMDs were exposed during seven consecutive 14-day periods and analyzed for PAHs. Relative percent differences (RPDs) were calculated to determine precision (reproducibility) in SPMD replicates. RPDs ranged from 13.9% to 56.0% (n=14). Variations in replicates encompassed SPMD preparation, deployment, exposure, retrieval, and analysis. Seven SPMDs were spiked at various intervals throughout the study with a mixture of all PAH analytes at 2.0 μg/g triolein per compound. Average percent recovery (n=7) varied from 52% to 82%. Method detection limits (MDLs) were also assessed by spiking ten SPMDs at 0.200 μg/g with equal amounts of a PAH mixture. Most MDLs for PAHs in SPMDs ranged from 0.054 to 0.178 μg/g triolein, however, if considering a 14-day exposure period, these MDLs can be translated into water concentrations of 2.1 ng/L to 13 ng/L. These values are as much as 2 000 times lower than MDLs for methods which employ solvent extraction and high performance liquid chromatography to directly measure PAHs in water. Blank SPMDs were prepared, and analyzed along with each set of field exposures and proved to be free of PAH contaminants above MDLs.