SPE absolute recoveries were assessed using the spiked ultrapure
water, surface water and tertiary treated effluent samples
at both a high concentration (100 ng L−1) and a low concentration
(10 ng L−1 except for dihydrotestosterone, which was spiked
at 20 ng L−1 since it has an MDL of 15.8 ng L−1). Because the
aim was to assess the loss of the target analytes during SPE
extraction, the isotope standards (50 ng) were added to the SPE
extracts only after the elution step for direct relative comparison to the analytes. The results of this experiment are presented in
Table 5.