Ex Situ Scanning Electrochemical Microscopy (SECM) Investigation of Bismuth- and Bismuth/Lead Alloy Film-Modified Gold Electrodes in Alkaline Medium Maiara Oliveira Salles , a Dario Battistel, b Alex Silva Lima, a Mauro Bertotti, a Salvatore Daniele* b a Institute of Chemistry, University of S¼o Paulo, Av. Professor Lineu Prestes, 748, 05513-970 S¼o Paulo, Brazil b Department of Physical Chemistry, University of Venice, Calle Larga, S. Marta, 2137, 30123 Venice, Italy tel. + 39 041 2348630; fax + 39 041 2348594 *e-mail: sig@unive.it Received: August 23, 2010; & Accepted: October 18, 2010 Abstract Scanning electrochemical microscopy (SECM) in feedback mode was employed to characterise the reactivity and microscopic peculiarities of bismuth and bismuth/lead alloys plated onto gold disk substrates in 0.1 mol L 1 NaOH solutions. Methyl viologen was used as redox mediator, while a platinum microelectrode was employed as the SECM tip. The metal films were electrodeposited ex situ from NaOH solutions containing either bismuth ions only or both bismuth and lead ions. Approach curves and SECM images indicated that the metal films were conductive and locally reactive with oxygen to provide Bi 3 + and Pb 2 + ions. The occurrence of the latter chemical reactions was verified by local anodic stripping voltammetry (ASV) at the substrate solution interface by using a mercury-coated platinum SECM tip. The latter types of measurements allowed also verifying that lead was not uniformly distributed onto the bismuth film electrode substrate. These findings were confirmed by scanning electron microscopy images. The surface heterogeneity produced during the metal deposition process, however, did not affect the analytical per- formance of the bismuth coated gold electrode in anodic stripping voltammetry for the determination of lead in al- kaline media, even in aerated aqueous solutions. Under the latter conditions, stripping peak currents proportional to lead concentration with a satisfactory reproducibility (within 5 % RSD) were obtained. Keywords: Bismuth film, Gold electrodes, Anodic stripping voltammetry, SECM, Alkaline medium DOI: 10.1002/elan.201000528 1 Introduction Since their introduction in 2000 by Wang et. al. [1], bis- muth film electrodes (BiFEs) have received much atten- tion, as alternative to mercury film electrodes, with re- gards to their use in anodic stripping voltammetry (ASV). Corresponding research efforts have produced a number of possible analytical applications, which are documented in several papers and reviews [1–10]. It is now generally established that the electroanalytical performance of BiFEs compare well with those of the analogous mercury film electrodes. In addition, BiFEs overcome environ- mental concerns related to mercury toxicity [1]. BiFEs can be prepared by either ex situ or in situ pro- cedures by electrodeposition of metallic bismuth from solutions containing bismuth ions on substrate materials such as various types of carbon materials [1–3, 8, 9, 11–15], copper [16, 17], platinum [3] and gold [3, 11, 18]. Carbon substrates have been the most common choice in ASV analysis, because of the wide cathodic window achievable, which is due to the high hydrogen overvoltage. Although much less employed, gold substrates have also displayed good performance for BiFEs preparation with the in situ procedure, especially for the detection of metal ions, such as Cd 2 + , Pb 2 + , Tl + , and In 3 + , which are deposited-strip- ped at not too negative potentials. It must be considered that the use of gold as substrate for bismuth film deposi- tion poses questions about interactions between bismuth and gold, which provides intermetallic species, reflecting on a number of bismuth stripping peaks [11, 18]. Another usual preference in the proposed method em- ploying in situ formed BiFEs is the use of acid media (i.e., acetate buffer has represented the dominating sup- porting medium) [1–3, 11–14, 17]. However, because of the chemical nature of Bi 3 + ions, BiFEs can also be oper- ated in highly alkaline media, as has been proven in a few papers for the detection of Pb, Cd, and Tl [12, 19]. Bismuth deposition from highly alkaline media is possi- ble, because Bi 3 + forms soluble complexes with hydroxide ions of the type [Bi(OH) n ] (3n) , (n = 1–4) [12, 19, 20] , which are readily reducible at the electrode surface: ½BiðOHÞ n  ð3nÞ þ 3e  ! Bi 0 þ nOH  ðn ¼ 1  4Þ ð1Þ The use of alkaline media along with BiFEs in ASV has provided some advantages in the ASV responses with Electroanalysis 2011, 23, No. 3, 595 – 603  2011 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim 595 Full Paper