A flow injection system based on chalcogenide glass sensors for the determination of heavy metals

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 analysed 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 mu M and about 1 mu M for the other metals. In our system chloride can be determined down to about 1 mu M alone and 20 mu M 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 mu l. 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. (C) 2000 Elsevier Science B.V. All rights reserved.