title: Determination of thyroxine in urine by cathodic stripping square-wave voltammetry.
abstract: A square-wave polarographic method for the determination of the amino acid thyroxine in urine, after isolation from the matrix on a C18 Sep-Pak cartridge and subsequent elution through a column packed with Amberlite IRA-400 anionic resin, was developed. The optimal working conditions for the application of the method were found to be pH 10, provided by a carbonate buffer, and a potential of -0.690 V during 10 min. The equilibration time was applied during 5 s, and potential scans were performed at a square-wave amplitude of 100 mV and a scan rate of 300 mV s-1, with a square-wave frequency of 100 Hz. The measuring-system response was linear over the thyroxine concentration range from 10 to 60 ng ml-1 and the detection limit achieved was 2.71 ng ml-1. The relative error and relative standard deviation obtained were 1.18 and 4.67%, respectively.
authors.affiliation: Departamento de Química Analítica, Facultad de Ciencias, Universidad Autónoma de Madrid, Ciudad Universitaria Cantoblanco, Spain.
authors.forename: L
authors.initials: L
authors.lastname: Hernández
authors.forename: P
authors.initials: P
authors.lastname: Hernández
authors.forename: O
authors.initials: O
authors.lastname: Nieto
mesh_terms: D004563:Electrochemistry; D006801:Humans; D007202:Indicators and Reagents; D013974:Thyroxine / Q000652:urine*
chemical_list: D007202:Indicators and Reagents; D013974:Thyroxine