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

Abstract

The use of cylindrical carbon ®ber microelectrodes (CFMEs) of various mm in length modi®ed with poly(3-methylthiophene) (P3MT) ®lms as amperometric microsensors for the LC-EC detection of catecholamines is reported. Cyclic voltammetry at the modi®ed microelectrodes of dopamine, epinephrine, catechol, serotonin and ascorbic acid showed electrocatalytic ability of the modi®ed 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 vav methanol:0.025 mol L À1 H 2 PO 4 À aHPO 4 2À solution of pH 7.0, showed no evidence of fouling of the modi®ed microelectrode surface. No cleaning or regeneration treatment was needed when working with the same polymer modi®ed microelectrode during the whole working day. Moreover, RSD values for i p lower than 5 % were obtained when amperometric measurements were carried out with three different P3MT-coated CFMEs. These modi®ed 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.

Simultaneous Diagnostic Assay of Catechol and Caffeine Using an in vivo Implanted Neuro Sensor

“…The optimum SW conditions were found to be as follows: 0.3 V amplitude, 40 Hz frequency, −0.6 V accumulation potential, 3 mV increment potential, 30 sec deposition time, and 5.0 pH electrolyte strength. The method was shown to be more sensitive than the previous DL [8][9][10][11][12][19][20][21][22]26 and could be attained at low working ranges for in vivo diagnosis. Tree electrode systems can be implanted into the fish and rat brain cell.…”

“…18 These techniques are applied only in in vitro conditions and are not applicable in in vivo direct assay. Moreover, catechol was studied in various analytical methods such as the capillary electrophoresis microchip with chemiluminescence method (DL: 10.0 uM catechol), 19 the voltammetric conducting polymer electrode (DL: 10 ppb catechol), 20 the amperometric detectors for liquid chromatographic method (DL: 1.5 uML −1 catechol), 21 and the electrochemical detectors in flow injection HPLC method (DL: 0.5 uML −1 catechol). 22 These methods were also applied only under laboratory conditions and required a complicated design, pre-treatment techniques, and expensive instruments.…”

Electrochemical Determination of Chlorophenols at Microcylinder Poly(3-methylthiophene) Modified Electrodes Based on a Previous Chemical Oxidation Using Bis(trifluoroacetoxy)iodobenzene

“…On the other hand, although modification of electrode surfaces with P3MT coatings has demonstrated some electrocatalytic activity towards the electrochemical oxidation of several organic analytes [15][16][17], including phenolic antioxidants [14], no useful voltammetric responses were obtained for the chlorophenols tested at P3MT-modified electrodes since the upper background limit of these modified electrodes appeared at lower potentials than those of the chlorophenols oxidation. Therefore, we decided to use the hypervalent iodine agent BTIB to chemically oxidize chlorophenols to the corresponding chlorinated quinones [13], so that the electrochemical monitoring of these quinones could be accomplished at much lower potentials.…”

“…A 10 mL electrochemical cell from BAS, Model VC-2 was also used. A flow cell based on a T-shape configuration previously described [16] was employed for flow injection measurements. The above-mentioned Ag=AgCl electrode inserted in the flow cell and the steel flow outlet tube were employed as reference and auxiliary electrodes, respectively.…”

“…This method is based on the chemical oxidation of CPs to the corresponding chlorobenzoquinones with very high yields using bis(trifluoroacetoxy)iodobenzene [13], and the electrochemical monitoring of these quinones using cylindrical carbon fiber microelectrodes (CFMEs) modified with poly(3-methylthiophene) (P3MT) coatings. We have demonstrated recently that the use of P3MT as a surface modifier of cylindrical CFMEs gives rise to voltammetric and amperometric sensors with important analytical advantages with respect to conventional electrodes or bare microelectrodes, both under batch and flowing conditions [14][15][16][17].…”