No abstract

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