Isotope ratio mass spectrometry in antidoping analysis: The use of endogenous reference compounds

Author:

de la Torre Xavier1ORCID,Jardines Daniel1,Curcio Davide1,Colamonici Cristiana1,Botrè Francesco12

Affiliation:

1. Laboratorio Antidoping Federazione Medico Sportiva Italiana Largo Giulio Onesti 1 00197 Rome Italy

2. Dipartimento di Medicina Sperimentale “Sapienza” Università di Roma Viale Regina Elena 324 00161 Rome Italy

Abstract

RationaleIsotope ratio mass spectrometry (IRMS) is an analytical technique required by the World Antidoping Agency (WADA) before releasing of an adverse finding for the abuse of pseudoendogenous steroids (i.e. testosterone). For every single individual, the delta 13C values (‰) of the selected target compounds (TCs, i.e. testosterone and/or its precursors/metabolites) are compared with those of endogenous reference compounds (ERCs). The aim of this work is to investigate the individual variation in the delta values of four different commonly used ERCs to establish the maximum acceptable variation, in order to detect potential outliers.MethodsRoutine urine samples collected for antidoping purposes were submitted to IRMS confirmation. After a specific liquid chromatographic purification of the analytes of interest, the final extracts were analyzed by gas chromatography/combustion (GC/C)‐IRMS. The selected ERCs monitored were pregnanediol, pregnanetriol, 11‐keto‐etiocholanolone and 11β‐hydroxyandrosterone. The obtained 13C delta values were statistically analyzed to evaluate their inter‐ and intra‐individual distribution.ResultsThe delta values of the ERCs studied showed a normal distribution and no major differences among genders were observed. As expected, there are differences depending on the geographical origin of the samples, reflecting different dietary habits and food sources. The intra‐individual dispersion, expressed as the standard deviation (SD) of the values of the studied ERCs, did not greatly exceed the instrumental error (0.5‰), demonstrating the good preservation of the delta values along the metabolic pathway.ConclusionsFor the selected ERCs of non‐sporting volunteers and the urinary specimens from more than 1000 sportsmen, we can propose a maximum SD of 0.54‰ and range of 1.2‰ for delta 13C values as acceptance criteria to detect potential outliers. These cases can be caused by the external masking effect of the administration of a substance modifying the delta values or outliers due to unforeseen procedural artifacts.

Funder

World Anti-Doping Agency

Publisher

Wiley

Reference18 articles.

1. WADA.TD2016 IRMS‐detection of synthetic forms of endogenous anabolic androgenic steroids by GC‐C‐IRMS.2016. Available:https://wada‐main‐prod.s3.amazonaws.com/resources/files/wada‐td2016irms‐detection_synthetic_forms_eaas_by_irms‐en.pdf

2. WADA.The World Anti‐Doping Code – The 2018 Prohibited List International Standard.2018. Available:https://www.wada‐ama.org/sites/default/files/prohibited_list_2018_en.pdf

3. Two Categories of 13C/12C Ratios for Higher Plants

4. Carbon isotope fractionation in plants

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