Table 3. Comparison of IS performances for each biphenyl analyte, arranged by proximity to analyte peak. RSDs and accuracies shown are averages for all male and female spiked replicates and the concentration for each sample represents the mean concentration of endogenous replicates. The best performing IS for each analyte is shown in bold. Values exceeding thresholds for RSD (> 15) and accuracy (< 70 or > 120%) are in gray. The slope of the line used for each calibration curve is shown, along with the correlation (R2) of calibrants. Separate low and high calibration curves help account for the high concentrations of gonadal steroids seen in some samples.