Bias estimation in the certification of steroid reference materials for carbon isotope delta measurements via elemental analyser and gas chromatography‐combustion‐isotope ratio mass spectrometry

Abstract

RationaleTwo new certified reference materials (CRMs) have been prepared providing three steroids certified for stable carbon isotope delta values, δ(13C) ‰. These materials have been designed to assist anti‐doping laboratories in validating their calibration method or to be 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 World Anti‐Doping Agency (WADA) Technical Document TD2021IRMS.MethodsCertification was performed using an elemental analyser‐isotope ratio mass spectrometry (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 gas chromatography‐combustion‐isotope ratio mass spectrometry (GC‐C‐IRMS) using a Trace 1310 GC coupled to a Delta V plus mass spectrometer via GC Isolink II.ResultsBased on the EA‐IRMS analysis, the materials were certified with δ(13C) 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 using GC‐C‐IRMS analysis and theoretical modelling based on purity assessment data.ConclusionsCareful 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.