title: Amperometric enzyme electrode for determination of theophylline in serum.
abstract: This paper describes an amperometric enzyme electrode for the rapid determination of theophylline in serum. The method is based on the catalysed oxidation of theophylline by the haem-containing enzyme theophylline oxidase. Results are presented for two approaches. First, ferrocene monocarboxylic acid was used as a mediator. The second-order rate constant was 1.1 x 10(3) 1 mol-1 s-1. Secondly, the organic conducting salt NMP.TCNQ was used to construct enzyme electrodes. These electrodes were employed for the rapid (60 s) measurement of theophylline in serum at a working potential of +100 mV versus Ag/AgCl. Linear calibration curves were obtained over the clinically relevant range (y = 0.13x + 0.22, n = 8). Caffeine, theobromine and 3-methylxanthine at levels up to 100 mg l-1 do not interfere and 1-methylxanthine shows cross-reactivity at concentrations greater than 50 mg l-1.
authors.affiliation: Department of Clinical Biochemistry, Medical School, University of Newcastle upon Tyne, UK.
authors.forename: C J
authors.initials: CJ
authors.lastname: McNeil
authors.forename: J M
authors.initials: JM
authors.lastname: Cooper
authors.forename: J A
authors.initials: JA
authors.lastname: Spoors
mesh_terms: D015374:Biosensing Techniques; D004553:Electric Conductivity; D004800:Enzymes, Immobilized; D005296:Ferrous Compounds / Q000737:chemistry*; D007700:Kinetics; D000075163:Metallocenes; D008991:Monitoring, Physiologic / Q000379:methods*; D009942:Organometallic Compounds / Q000737:chemistry*; D013806:Theophylline / Q000097:blood*; D013997:Time Factors
chemical_list: D004800:Enzymes, Immobilized; D005296:Ferrous Compounds; D000075163:Metallocenes; D009942:Organometallic Compounds; D013806:Theophylline; C004998:ferrocene