title: Voltammetric behaviour of morphine at a glassy carbon electrode and its determination in human serum by liquid chromatography with electrochemical detection under basic conditions.
abstract: The electrochemical oxidation of morphine was studied at pH values of between 7.00 and 12.00 by cyclic voltammetry and chronoamperometry at a planar glassy carbon electrode. The peak potential was dependent on pH over the range 7.00-9.75; it was independent of pH above the latter value, indicating a pKa value of 9.75. The peak current was found to be independent of pH, ionic strength of phosphate buffer (0.02-0.1 mol dm-3) and percentage of acetonitrile (0-40% v/v). The oxidation was found to occur in three steps; these are considered to result from a one-electron oxidation of the phenoxide group, followed by a one-electron loss from the oxidation product, pseudomorphine, and finally a two-electron loss from a tertiary amine group. A simple method of analysis by high-performance liquid chromatography was developed which employed a column packed with a reversed-phase, pH-stable, octadecylsilane-modified silica. Separation was achieved with a mobile phase containing 20% v/v acetonitrile in 0.05 mol dm-3 phosphate buffer, pH 11.0. Amperometric detection was carried out with an applied potential of +0.45 V versus Ag-AgCl. The detection limit was 1.24 x 10(-13) mol of morphine injected. The detector gave a linear response from 1.2 x 10(-12) to 4.0 x 10(-10) mol of morphine injected. The extraction method required 0.5 ml of serum, and no solvent evaporation was needed. The recovery of morphine was 80.9%. The method gave a linear response to at least 15.0 x 10(-7) mol dm-3.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Chemical Pathology, Royal Devon and Exeter Hospital, Heavitree, UK.
authors.forename: P H
authors.initials: PH
authors.lastname: Jordan
authors.forename: J P
authors.initials: JP
authors.lastname: Hart
mesh_terms: D002244:Carbon / Q000737:chemistry*; D002853:Chromatography, Liquid / Q000379:methods; D004563:Electrochemistry / Q000379:methods; D004566:Electrodes; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009020:Morphine / Q000097:blood* / Q000737:chemistry; D010084:Oxidation-Reduction
chemical_list: D002244:Carbon; D009020:Morphine