Microcylinder Polymer Modified Electrodes as Amperometric Detectors for Liquid Chromatographic Analysis of Catecholamines

The use of cylindrical carbon fiber microelectrodes (CFMEs) of various mm in length modified with poly(3-methylthiophene) (P3MT) films as amperometric microsensors for the LC-EC detection of catecholamines is reported. Cyclic voltammetry at the modified microelectrodes of dopamine, epinephrine, catechol, serotonin and ascorbic acid showed electrocatalytic ability of the modified surface. This allowed the application of low potentials (+0.35 V) for the amperometric detection of the above-mentioned compounds. Flow injection measurements carried out using a 2:98 v/v methanol:0.025 mol L–1 H2PO4–/HPO42– solution of pH 7.0, showed no evidence of fouling of the modified microelectrode surface. No cleaning or regeneration treatment was needed when working with the same polymer modified microelectrode during the whole working day. Moreover, RSD values for ip lower than 5 % were obtained when amperometric measurements were carried out with three different P3MT-coated CFMEs. These modified microelectrodes have also shown to be suitable for amperometric detection in HPLC. A mobile phase composed of 2:98 % methanol:phosphate buffer solution of pH 7.0 allowed a good separation of mixtures of ascorbic acid, epinephrine, dopamine, serotonin and catechol with detection limits ranging between 14 and 48 pmol. Furthermore, as an application, the determination of those compounds in spiked serum samples, was accomplished with good results.