A new sildenafil analogue, propoxyphenyl isobutyl aildenafil has been found in trace quantity from one health supplement. It has been purified by preparative high performance liquid chromatography (HPLC). The structural elucidation of this compound has been carried out using high-resolution Orbitrap mass spectrometry under two fragmentation modes, namely High energy Collision Dissolution (HCD) and Collision Induced Dissolution (CID). Under MS3 experiments and CID mode, the isobutyl-bonded fragments of propoxyphenyl isobutyl aildenafil at m/z 313 and 297 have been compared with the reference ions derived from isobutyl sildenafil. The accurate mass measurement of each product ions has been carried out with the aid of Mass Frontier software (version 5.0). The mass error of all product ions is not more than 5.0 ppm.