Abstract: A chalcogenide glass Cr(VI) selective electrode has been tested. The Nernst plot is S-shaped, and the slope of the mid linear portion is about 90 mV decade-1. An analytically useful potential change from about 10^-6-10^-3 M Cr(VI) results. The response is related to a surface sensing mechanism, which is of redox nature. The electrode is generally sensitive towards compounds with high oxidising and reducing powers but insensitive towards ions with poor oxidising or reducing capacities. The response is slow and depends on the reduction potential of the analyt compounds, the exposure time and the concentration level. Therefore a flow-Injection-Analyser-system (FIA) is developed for the determination of Cr(VI) in aqueous environments. For the reduction of response times thereby enhancing the performance of the electrode reducing agents or electrochemical reduction between FIA injections were successfully employed. It is concluded, that to a large extend the FIA-system can be optimized to aqueous environments with Cr(VI) concentrations down to 10^-6 M. Special applications is under development for on-line measurements of Cr(VI) for production control in the electroplating industries.

Abstract: A flow injection system was developed for simultaneously measuring the content of heavy metal ions [Pb(II), Cd(II), Cu(II), and Cr(VI)] in incinerating plant smokes.

Abstract: A flow injection set-up for the determination of Pb(II), Cr(VI), Cu(II), Cd(II) using chalcogenide glass chemical sensors (electrodes) is presented. Seven electrodes are used to determine the four metals and also chloride ions and the signals are analyzed using multivariate analysis method, including artificial neural networks. The background solution is 1 M nitric acid. It is divided in two lines where the first one is mixed with 1.2 M sodium acetate and the other one is 1 M nitric acid. The Hg(II), Cr(VI) and Ag(I) sensors are placed in the acid line while the Pb(II), Tl(I), Cd(II) and Cu(II) electrodes are placed in the buffered line. The detection limit for Pb(II) was about 3 µM and about 1 µM for the other metals. In our system chloride can be determined down to about 1 µM alone and 20 µM simultaneously with the other species. The average error for the determination of the metals in the range from the detection limit up to about 3 mM was 10^-15% for Pb(II), Cr(VI), Cu(II) and Cd(II) and about 30% for Cl-. The parameters for the flow injection system were: flow rate 0.5 ml/min and sample Volume 500 µl. The peak widths were 100-300 s allowing a theoretical measurement rate of 15 per hour. In practice, sampling rates of about 7-10 times per hour are realistic. The system is developed as a step forward to on-line measurements of exhaust gases from waste incineration plants.