This paper describes an analytical method using a nuclear-related technique for the detection of forbidden doping substances
in the urine of race horses. The proposed method, adapted from the Méthode Alcaline Sur C-18 developed by the French Laboratoire
de Contrôle Antidopage, is based on gas chromatography separation followed by mass spectrometry (GC-MS). The method was validated
for caffeine, identified as the most frequent doping substance in the Brazilian horseracing activity. This validation is also
a major requirement to achieve ISO/IEC 17025 laboratory accreditation. The validation has led to several metrological challenges
because the decisions are largely based on qualitative results (“false-positive” and/or “false-negative”) and the degree of
accuracy, as well as the traceability had to be determined in the absence of certified matrix reference materials.