Direct isotopically labelled analogues were used for 8 of the 12 hormones and satisfactory
isotope standards were identified for the remaining 4 hormones. Method detection levels (MDLs)
were determined to describe analyte concentrations sufficient to provide a signal with 99% certainty
of detection. The established MDLs for most analytes were 1–5 ng L−1 in a variety of aqueous matrices.
However, slightly higher MDLs were observed for etiocholanolone, androstenedione, testosterone, levonorgestrel
and dihydrotestosterone in some aqueous matrices. Sample matrices were observed to have
only a minor impact on MDLs and the method validation confirmed satisfactory method stability over
intra-day and inter-day analyses of surface water and tertiary treated effluent samples.