Bias Estimation in the Certification of Steroid Reference Materials for Carbon Isotope Delta Measurements via EA- and GC-C-IRMS.

Abstract

Two new CRMs have been prepared providing three steroids certified for stable carbon isotope delta values, δ(13 C) ‰. These materials have been designed to assist anti-doping laboratories validate their calibration method or employed as calibrant for stable carbon isotope measurements of Boldenone, Boldenone Metabolite 1 and Formestane. These CRMs will allow for accurate and traceable analysis in compliance with WADA Technical Document TD2021IRMS. Certification was performed using an EA-IRMS primary reference method on the bulk carbon isotope ratios of nominally pure steroid starting materials. EA-IRMS analyses were carried out on a Flash EA Isolink CN coupled via a Conflo IV to a Delta V plus Mass Spectrometer. Confirmation analysis was performed by GC-C-IRMS using a Trace 1310 GC coupled to a Delta V plus Mass Spectrometer via GC Isolink II. Based on the EA-IRMS analysis the materials were certified with δ(13 C) values of -30.38 ‰ (Boldenone), -29.71 ‰ (Boldenone Metabolite 1) and 30.71 ‰ (Formestane). Noting that the assumption of 100% purity in the starting materials has the potential to introduce bias this was investigated by GC-C-IRMS analysis and theoretical modelling based on purity assessment data. Careful application of this theoretical model was shown to provide reasonable estimates of uncertainty while avoiding the introduction of errors associated with analyte specific fractionation during GC-C-IRMS analysis.