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8An isotope dilution mass spectrometry (IDMS) method for the determination of selected 9 endogenous anabolic androgenic steroids (EAAS) in urine by UHPLC-MS/MS has been 10 developed using the isotope pattern deconvolution (IPD) mathematical tool. The method has 11 been successfully validated for testosterone, epitestosterone, androsterone and 12 etiocholanolone, employing their respective deuterated analogs using two certified reference 13 materials (CRM). Accuracy was evaluated as recovery of the certified values and ranged from 14 75% to 108%. Precision was assessed in intraday (n=5) and interday (n=4) experiments, with 15RSDs below 5% and 10% respectively. The method was also found suitable for real urine 16 samples, with limits of detection (LOD) and quantification (LOQ) below the normal urinary 17 levels. The developed method meets the requirements established by the World Anti-Doping

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17Three quantification methodologies, namely calibration with internal standard (Cal-IS, non-weighted), 18 weighted calibration with internal standard (wCal-IS) and isotope pattern deconvolution (IPD) have been 19 used for the determination of testosterone in urine by LC-MS/MS. Uncertainty has been calculated and 20 compared for the three methodologies through intra-and inter-laboratory reproducibility assays. IPD 21showed the best performance for the intra-laboratory reproducibility, with RSD and combined uncertainty 22 values below 4% and 9% respectively. wCal-IS showed similar performance, while Cal-IS where not constant 23 and clearly worse at the lowest concentration assayed (2 ng/mL) reaching RSD values up to 16%. The inter-24 laboratory assay indicated similar results although wCal-IS RSD (20%) was higher than IPD (10%) and Cal-IS 25 get worse with RSD higher than 40% for the lowest concentration level. Uncertainty budgets calculated for 26 the three procedures revealed that intercept and slope were the most important factors contributing to 27 uncertainty for Cal-IS. The main factors for wCal-IS and IPD were the volumes of sample and/or standard 28 measured. 29 30 INTRODUCTION 31

Reliable determination of endocrine disrupting compounds in water.