title: Bioanalysis of captopril: two sensitive high-performance liquid chromatographic methods with pre- or postcolumn fluorescent labeling.
abstract: This study describes the development and comparison of two HPLC methods for the analysis of the antihypertensive drug captopril. The first method is based on a precolumn derivatization of captopril with the fluorescent label monobromobimane (MBB). The second method is based on a postcolumn reaction with the fluorescent reagent o-phthaldialdehyde (OPA). Since the disulfide metabolites of captopril can be reconverted to the active drug in vivo, the bioanalysis of captopril should involve both the determination of its free thiol form (free captopril) and the total amount of free thiol and reducible disulfides (total captopril). For total captopril analysis, disulfides were reduced with tributylphosphine (TBP) prior to protein precipitation. Since the reducing agent interfered with the MBB derivatization reaction, this method was not suitable for total captopril analysis. Both methods were validated for the bioanalysis of free captopril in human plasma. After removal of plasma proteins, samples were analyzed without an additional extraction procedure. The limit of quantitation in plasma was 12.5 ng/ml for the MBB method (limit of detection 30 pg) and 25 ng/ml for the OPA method (limit of detection 50 pg). The OPA method was also validated for total captopril analysis in human plasma and urine. The limit of quantitation was 25 ng/ml in plasma and 250 ng/ml in urine (limit of detection 50 pg). We conclude that for the analysis of free captopril the precolumn MBB method is superior to the OPA method since only the derivatization reaction has to be carried out immediately. The postcolumn OPA method is especially suitable for the analysis of total captopril since reducing reagents and high concentrations of endogenous thiols do not interfere with the derivatization reaction.
authors.affiliation: Groningen Institute for Drug Studies (GIDS), Department of Pharmacokinetics and Drug Delivery, Netherlands.
authors.forename: R J
authors.initials: RJ
authors.lastname: Kok
authors.forename: J
authors.initials: J
authors.lastname: Visser
authors.forename: F
authors.initials: F
authors.lastname: Moolenaar
authors.forename: D
authors.initials: D
authors.lastname: de Zeeuw
authors.forename: D K
authors.initials: DK
authors.lastname: Meijer
mesh_terms: D000806:Angiotensin-Converting Enzyme Inhibitors / Q000097:blood* / Q000493:pharmacokinetics; D000959:Antihypertensive Agents / Q000097:blood* / Q000493:pharmacokinetics; D001643:Bridged Bicyclo Compounds; D002216:Captopril / Q000097:blood* / Q000493:pharmacokinetics; D002851:Chromatography, High Pressure Liquid; D005456:Fluorescent Dyes; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence; D009764:o-Phthalaldehyde
chemical_list: D000806:Angiotensin-Converting Enzyme Inhibitors; D000959:Antihypertensive Agents; D001643:Bridged Bicyclo Compounds; D005456:Fluorescent Dyes; D009764:o-Phthalaldehyde; D002216:Captopril; C028381:monobromobimane