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Published:
Journal of Analytical Toxicology,
ISSN 0146-4760,
Volume 31, Number 9, November/December,
pp.543-548
Results of Stability Studies with Doping
Agents in Urine
P. Van Eenoo, L. Lootens, A. Spaerkeer,
W. Van Thuyne, K. Deventer, and F.T. Delbeke
DoCoLab, UGent, Department of Clinical Chemistry, Microbiology
and Immunology, Technologiepark 30, B-9052 Zwijnaarde, Belgium
For a correct interpretation of analytical results
in doping control, knowledge on the stability of prohibited substances
in the urinary matrix is a prerequisite. So far, limited data
is available on the stability of prohibited substances in unaltered
urine because most of the studies investigating the stability
of drugs have used stabilized, sterilized, or filtered urine.
In this work, the long-term stability of ephedrine, methylephedrine,
cathine, 19-norandrosterone glucuronide, and a wide range of
diuretics was determined over a period of 9 months at –20°C,
4°C, 22°C, and 37°C. Short-term stability, including
the influence of 6 freeze-thaw cycles and 15 h storage at 60°C,
was also investigated. Often, a tolerance limit of 15%, similar
to what is commonly used in the evaluation of precision data
during method validation, is used to evaluate stability. This
paper describes an alternative approach, using measurement uncertainty
data to evaluate long-term stability with a probability of 95%,
and proposes a simple alternative for investigating the stability
for non-threshold substances. The results indicate that all the
investigated substances are stable (a = 0.05) when stored at –20°C
and 4°C, but that at higher temperatures significant degradation
effects can occur. The study also shows that degradation can
be dependent on the urinary matrix and that the results from
stability studies using stabilized, filtered, or sterilized urine
can underestimate degradation effects.
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