Eduardo M. Richter 1 José A. Fracassi da Silva 2 Ivano G. Rolf Gutz 1 Claudimir L. do Lago 1 Lúcio Angnes 1 1 Instituto de Química 2 Escola Politécnica, Universidade de São Paulo, São Paulo, SP, Brazil Disposable twin gold electrodes for amperometric detection in capillary electrophoresis We describe a simple and easy way to construct gold microelectrodes for ampero- metric detection in capillary electrophoresis (CE). The gold microelectrodes, in single or twin sets, were obtained from recordable compact discs (gold-sputtered type), which present highly reproducible surface characteristics. The performance of these electrodes was evaluated by using a home-made CE equipment. The basic steps for the electrode construction are: drawing on a microcomputer; laser printing of the design on wax paper; heat-transfer of the toner onto the gold surface of a peeled recordable compact disc (CD-R); etching of the gold layer from unprinted regions; removal of the toner with a solvent; sealing of unused electrode areas with varnish. One electrode at a time was connected to a potentiostat (or two, to a bipotentiostat) and operated in a wall jet configuration relative to the CE capillary outlet. The ampero- metric signals were integrated for quantification purposes. Repetitive injections (n = 10) of a mixture containing iodide, ascorbic acid, dipyrone, and acetaminophen (20, 200, 500, and 100 mM), presented relative standard deviations of 2.9, 4.5, 6.1, and 4.0%, respectively. For these analytes, the detection limits (S/N = 3, 30 s of 100 mm hydro- dynamic injection) were 0.1, 0.5, 3.1, and 1.1 mM, respectively. Keywords: Amperometry / Capillary electrophoresis / Electrochemical detection / Gold electrode DOI 10.1002/elps.200305960 1 Introduction Since its introduction in 1987 by Wallingford and Ewing [1], many efforts have been directed to the development of amperometric detection (AD) in capillary electrophoresis (CE). In fact, a great variety of cell and electrode designs, as well as electrode materials, have been described [2–6]. The application of CE-AD to different classes of com- pounds, including small ions and molecules, biologically relevant species and macromolecules, proved the poten- tial and versatility of this type of detection applied in CE. The high electric field applied to the capillary to promote the analyte’s separation may cause serious interference with AD, raising the baseline noise and, consequently, re- ducing the limits of detection [7]. Additionally, the align- ment between the capillary and working electrode showed to be crucial for the reproducibility and detectability. Earlier developments made use of micropositioners to precisely adjust these distances, but some workers reported the use of simplified schemes for the electrode alignment [8– 11]. In these cases, the wall-jet configuration has been successfully employed. Alternatively, the working elec- trode can be deposited or immobilized on the capillary out- let, but this approach results inconvenient when the capil- lary needs to be changed [12]. Gold electrodes are widely used in electroanalysis, including CE-AD [13–24], mainly in applications that involve excursions in positive potential region. Angnes and co-workers [25–27] have demonstrated that gold electrodes can be promptly obtained from recordable compact discs (CD-Rs). Due to the highly controlled CD-R fabrication process, their gold deposits exhibit highly reproducible thickness, orientation and roughness, and are firmly adhered to a flat substrate of polycarbonate [28]. Additionally, since two polymer layers are added over the gold film, these surfaces are protected from scratches and environmental contaminants until the poly- mer layers are chemically removed. In this work, an easy and versatile way for construction of microamperometric detectors using disposable gold electrodes for use in CE is described, stemming from two recent works. The first one presents a process for microfabrication based on a xerographic process for con- Correspondence: Prof. Lúcio Angnes, Instituto de Quimica, Uni- versidade de São Paulo, Av. Prof. Lineu Prestes, 748, Bloco 12 Superior, 05508-900São Paulo, SP, Brazil E-mail: luangnes@iq.usp.br Fax: 155-11-3091-2150 Abbreviations: AD, amperometric detection; CD-R, recordable compact disc; CTAH, cetyltrimethylammonium hydroxide; ED, electrochemical detection; WE, working electrode Electrophoresis 2004, 25, 2965–2969 2965  2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim CE and CEC