title: Direct and simultaneous high-performance liquid chromatographic assay for the determination of p-aminobenzoic acid and its conjugates in human urine.
abstract: Procedures based on high-performance liquid chromatography (HPLC) were developed for identifying and measuring p-aminobenzoic acid (PABA) and its conjugate metabolites in human urine after oral doses of PABA. p-Aminohippuric acid (PAH), PABA, p-acetamidohippuric acid (PAHA) and p-acetamidobenzoic acid (PADB) in urine were resolved and determined by HPLC simultaneously and directly without extraction. A mobile phase consisting of 3% (v/v) acetonitrile in distilled water containing 0.005 M 1-heptanesulphonic acid in glacial acetic acid (PIC-B7) at pH 3.3 was eluted at 1 ml/min through a C18 Spherisorb column, followed by UV detection at 280 nm. After hydrolysis of urine samples at 37 degrees C for 3 h with beta-glucuronidase, the amounts of PABA-glucuronide and PADB-glucuronide were also determined. The retention times of PAH, a dominant peak which disappeared after hydrolysis, PABA, DABA (3,5-diaminobenzoic acid, as the internal standard), PAHA and PADB were 11.8, 14, 15, 18, 24 and 46 min, respectively. The 24-h urinary recoveries of PAH, PAHA, PADB, PADB-glucuronide, PABA and PABA-glucuronide after separate oral doses of 200 and 800 mg of PABA in one healthy subject were 43.4 and 48.1, 7 and 29.1, 11.2 and 11.8, 34.8 and 6.6, 0.2 and 0.3, and 1.0 and 2.4%, respectively. It is interesting that at high dose (800 mg) saturation of glucuronidation of PADB (N-acetylated PABA) appeared to occur, which resulted in an increase in the formation of PAHA, the glycine conjugate of PADB. Over 90% of the oral dose was accounted for by 8 h after administration.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, Chinese University of Hong Kong, Shatin.
authors.forename: K
authors.initials: K
authors.lastname: Chan
authors.forename: J O
authors.initials: JO
authors.lastname: Miners
authors.forename: D J
authors.initials: DJ
authors.lastname: Birkett
mesh_terms: D010129:4-Aminobenzoic Acid / Q000493:pharmacokinetics / Q000652:urine*; D062365:Aminobenzoates / Q000652:urine*; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D007202:Indicators and Reagents; D010130:p-Aminohippuric Acid / Q000652:urine; D062366:para-Aminobenzoates
chemical_list: D062365:Aminobenzoates; D007202:Indicators and Reagents; D062366:para-Aminobenzoates; C023730:Acedoben; D010129:4-Aminobenzoic Acid; D010130:p-Aminohippuric Acid