Determination of sulfur species using a glassy-crystalline chalcogenide membrane C. Cali * , G. Taillades, A. Pradel, M. Ribes Laboratoire de Physicochimie de la Matie Áre Condense Âe, Universite  Montpellier II, UMR 5617, C.C. 003, Place Euge Áne Bataillon, F-34095 Montpellier Cedex 5, France Abstract Anewpotentiometricsul®desensorbasedonchalcogenideglassy/crystallineCu±As 2 S 3 alloysisdescribed.Theanalyticalcharacteristics oftheseion-selectiveelectrodeswerefullyinvestigatedintermsofsensitivity,selectivity,reproducibilityandcomparedtotheconventional method for sul®de determination. Quasi-Nernstian responses associated to a limit of detection close to 10 6 M were observed. While low selectivity coef®cients were obtained versus several anions. The most important characteristic of this sensor was the ability to detect the sul®de species at neutral or pH or even acidic pH. The sensor was applied to the long term in situ monitoring of sulphide concentration in thermal bath. On site measurements show good reproducibility, long term stability >3 months) and allow monitoring of sul®de concentration. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Chalcogenide glass; Sul®de; Ion-selective electrodes 1. Introduction The importance of sul®de compounds in biological pro- cesses has been widely demonstrated and it is well known that the generation of sul®de is linked to a number of vital, chemical, physical, and biochemical processes. Three main methodsarecommonlyusedforthedeterminationofsul®de in solution [1]:  Thecolorimetricmethod,i.e.themethylenebluemethod, is based on the reaction of sulfide, ferric chloride and dimethyl-p-phenylenediaminetoproducemethyleneblue which absorbs at 664 nm.  The iodometric method based on the oxidation of sulfide by iodide in acidic solution followed by a back titration with sodium thiosulphate solution.  The potentiometric method using a conventional silver sulfide electrode after sample handling and conditioning to high pH. Chalcogenide glasses have been used as membranes in ion-selective electrodes for determination of heavy metal ions Cu 2 , Cd 2 , Pb 2 , Hg 2 , Fe 3 and Ag  ) [2±5]. Chalcogenide glass sensors have a high stability in acid and oxidizing media and are characterized by a better selectivity than crystalline ion sensors. Anion-selective chalcogenide membranes are less known. Bohnke et al. [6] reported the response of a PbI 2 based sensor in iodide and sul®de solutions. In addition, Vlasov et al. [7] studied theanalyticalcharacteristicsoftheglassy-crystallineAgBr± Ag 2 S±As 2 S 3 alloysandconcludedthatthesensorsshoweda high sensitivity to bromide ion. Jasinski et al. [8] were the ®rst to use a Cu±As 2 S 3 based sensor. In this case the aim was the determination of Cu 2 ions in aqueous solutions. They found that the electro- chemically active component is the crystalline ``Sinnerite'' phaseCu 6 As 4 S 9 ).StableNernstianresponsesforconcentra- tions lying from 10 2 to 10 5 M copperII) were obtained. The purpose of this study is to investigate the electro- analytical characteristics of several Cu±As 2 S 3 alloys con- tainingdifferentamountsofcoppermetal.Thestructureand electrical conductivity of the membranes are reported. The electrochemicalresponsesincludingtheeffectofpHandof several interfering ions are also studied. 2. Experimental procedure Arsenic trisul®de was prepared by heating the elements 99.999%) in a sealed quartz ampoule at 6008C for about 8±12h. The sensor materials Cu x As 2 S 3 ) 1x x  2±10at.%) were synthesized by melting As 2 S 3 and the appropriate amount of copper metal 99.99%, Aldrich) at 9508C for 24 h in silica tubes evacuated to 10 5 Pa. Ampoules were Sensors and Actuators B 76 2001) 560±564 * Corresponding author. 0925-4005/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0925-400501)00631-1