title: Determination of pethidinic acid and norpethidinic acid in urine by mass fragmentography after extractive alkylation.
mesh_terms: D000478:Alkylation; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D008614:Meperidine / Q000031:analogs & derivatives* / Q000652:urine*
chemical_list: D008614:Meperidine