Naphthoquinone derivatives were extracted from the acidified urine by ethyl acetate and analyzed by high performance liquid chromatography with UV detection (HPLC/UV) and mass-spectrometric detection (HPLC/MS). 
HPLC/UV
Naphthoquinone derivatives were extracted from the acidified urine by ethyl acetate and analyzed by high performance liquid chromatography with UV detection (HPLC/UV) and mass-spectrometric detection (HPLC/MS). 
HPLC/MS