Improved calibration and measurement uncertainty estimation for stable carbon isotope ratio measurements for the detection of steroid abuse

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Copyright: Munton, Ellaine
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Abstract
Testosterone is an endogenous steroid which may be abused by athletes for performance enhancement. As testosterone is naturally present in the body, identifying administration requires an ability to demonstrate whether the testosterone present in a sample has an origin outside the normal metabolic processes. Analysis of the stable carbon isotopes of urinary steroids is used to determine whether administration of synthetic testosterone has occurred. The aims of this project were to find the best approach to measurement uncertainty and decision limit estimation of urinary steroid carbon isotope ratio measurement results for sports drug testing analysis, and to determine how to minimise these measurement uncertainties. The sample preparation was studied, and the steps with the greatest potential for isotopic fractionation were optimised to minimise the introduction of measurement bias during sample preparation. A new approach for the calculation of carbon isotope ratios from Isotope Ratio Mass Spectrometer measurements was developed. The measurement uncertainty estimation was greatly simplified when using this calculation approach, compared to the more commonly used iterative calculation approaches. The optimised method was found to be rugged, accurate, and suitable for the measurement of carbon isotope ratios of urinary steroids for the detection of testosterone administration. The traceability of the measurements to the carbon isotope ratio embodied in the internationally recognised standard for carbon isotope ratio measurement results was established. When using the new calculation approach, the expanded uncertainties of the carbon isotope ratio measurement results at the 95 % level of confidence were between 1.6 and 4.0 . For a commonly used iterative calculation approach, the expanded uncertainties of the carbon isotope ratio measurement results at the 95 % level of confidence were between 2.0 and 3.9 . The estimation of the measurement uncertainty when using the iterative calculation approach was difficult, due to the complexity of the measurement function and the calculation of the sensitivity coefficients. By finding simple relationships between the measurement function input factors and the calculated sensitivity coefficients, approximations of these sensitivity coefficients were developed. These approximations gave very similar combined measurement uncertainty estimations compared to estimations made using calculated sensitivity coefficients.
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Author(s)
Munton, Ellaine
Supervisor(s)
Gooding, Justin
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Publication Year
2013
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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