Abstract19‐Norandrosterone (19‐NA) is the main metabolite of nandrolone and/or its precursors, which can be found naturally in human urine in trace amount. Gas chromatography–combustion–isotope ratio mass spectrometry (GC–C–IRMS) confirmation procedure can be used to identify a potential exogenous origin of 19‐NA in urine sample. Sample purification for GC–C–IRMS analysis is crucial to the whole confirmation procedure because the concentration of 19‐NA in the urine to be tested is very low. Online two‐dimensional high‐performance liquid chromatography (2D–HPLC) clean‐up procedure with high separation capacity is used to isolate and enrich 19‐NA as a sample pretreatment process. Linearity, lowest detectable concentration, uncertainty, and selectivity of the method are validated according to the World Anti‐doping Agency's (WADA) requirement. Isotope fractionation effect was not observed during the 2D‐HPLC purification process. The validated method provides a high efficient and convenient confirmation procedure to determine the origin of 19‐NA.