Analytica Chimica Acta 556 (2006) 145–150 A highly stable and sensitive chemically modified screen-printed electrode for sulfide analysis Dong-Mung Tsai, Annamalai Senthil Kumar, Jyh-Myng Zen ∗ Department of Chemistry, National Chung Hsing University, 250 Kuo-Kuang Road, Taichung 40217, Taiwan Received 15 March 2005; received in revised form 15 May 2005; accepted 17 May 2005 Available online 5 July 2005 Abstract We report here a highly stable and sensitive chemically modified screen-printed carbon electrode (CMSPE) for sulfide analysis. The CMSPE was prepared by first ion-exchanging ferricyanide into a Tosflex anion-exchange polymer and then sealing with a tetraethyl orthosilicate sol–gel layer. The sol–gel overlayer coating was crucial to stabilize the electron mediator (i.e., Fe(CN) 6 3- ) from leaching. The strong interaction between the oxy–hydroxy functional group of sol–gel and the hydrophilic sites of Tosflex makes the composite highly rigid to trap the ferricyanide mediator. An obvious electrocatalytic sulfide oxidation current signal at ∼0.20 V versus Ag/AgCl in pH 7 phosphate buffer solution was observed at the CMSPE. A linear calibration plot over a wide range of 0.1 M to 1 mM with a slope of 5.6 nA/M was obtained by flow injection analysis. The detection limit (S/N = 3) was 8.9 nM (i.e., 25.6 ppt). Practical utility of the system was applied to the determination of sulfide trapped from cigarette smoke and sulfide content in hot spring water. © 2005 Elsevier B.V. All rights reserved. Keywords: Ferricyanide; Tosflex; Sol–gel; Screen-printed electrode; Sulfide 1. Introduction Sulfide toxicity is well known and the corresponding risk is associated with exposure in several occupational settings [1–6]. Continuous and high concentration exposure of sulfide can cause various physiological and biochemical problems. Therefore easy and fast detecting analytical tools are press- ing need to effectively control the risk of sulfide-toxicities. Electrochemical detection assays using chemically modified electrodes (CMEs) were found to be advantageous for a wide range of practical assays in field analysis [7]. Electroanal- ysis can permit miniature assemblies/chips with disposable type of low-cost screen-printed electrodes (SPEs) [8]. Reli- able measurements of dissolved sulfide in the environment require analysis immediately on sample collection because of the rapid oxidation rate of sulfide by dissolved oxygen. Vari- ∗ Corresponding author. Tel.: +886 4 22840411/506; fax: +886 4 22854007. E-mail address: jmzen@dragon.nchu.edu.tw (J.-M. Zen). ous CMEs based on different modifiers, pre-oxidized nickel, palladium and copper electrodes were reported for the sulfide assays [9–18]. However, most of these systems are limited to practical extendibility and the common problems of stability and sensitivity are yet to be improved. We report here a highly stable and sensitive chemi- cally modified screen-printed carbon electrode (CMSPE) for sulfide analysis. The CMSPE was prepared by first ion-exchanging ferricyanide into a Tosflex anion-exchange polymer (SPE/Ts-FeCN) and then sealing with a tetraethyl orthosilicate sol–gel layer (SPE/Ts-FeCN/SG). In general, sol–gel-based systems with efficient electrocatalysis, fouling protection, exclusion of interferants, are of great importance for the development of chemical sensors. Very recently, our group applied such a system for the mediated oxidation of ascorbic acid in neutral pH with high stability for repetitive measurements [19,20]. The sol–gel overlayer was essential to stabilize the Fe(CN) 6 3- -Tosflex system without any foul- off and deterioration behavior in flow injection analysis. The chemical interaction between the hydrophilic sites of Tos- 0003-2670/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2005.05.038