ANALYTICA CHIMICA ACTA zyxwvutsrqpon ELSEVIER Analytica Chimica Acta 308 (1995) 115-121 Flow-through tubular ion-selective electrodes responsive to anionic surfactants for flow-injection analysis J. Alonso, J. Barb, J. Bartroli, J. Siinchez, M. de1 Valle * zyxwvutsrqponmlkjihgf Grup de Sensors i Biosensors, Departament de Quimica, Unicersitat Autbnoma de Barcelona, 08193 Bellaterra, Spain Received 2 August 1994; revised manuscript received 19 September 1994 zyxwvutsrqponmlkjihgfedcbaZYX Abstract A flow-injection system based on potentiometric detection and designed for the monitoring of anionic surfactant content of printing plates washing solutions is described. Two new PVC membrane ion-selective electrodes, constructed with an all-solid-state tubular flow-through design, are used. The sample, with high ionic strength and extremely alkaline pH, is conditioned in a two-channel flow-injection system, allowing for surfactant determination in the 1 X lop4 to 1 X 10e3 M range, with NaOH contents up to 0.3 M. Keywords: Flow system; Ion selective electrodes; Printing plates 1. Introduction Anionic surfactants comprise a large group of synthetic substances with multiple uses in the indus- trial and domestic field. Their wide consumption makes relevant their determination during the manu- facturing steps or at environmental level. The routine procedure for the industrial control of detergents is based on a two-phase titration [l], but it has several drawbacks, namely it is time-consuming, uses haz- ardous solvents, and lacks automation possibilities. The development of electrodes sensitive to an- ionic surfactants represents an attractive alternative, normally using the potentiometric titration technique, to these analytical determinations, and with added advantages of easy automation, reduction of the de- * Corresponding author. termination time to a few minutes, a lower consump- tion of reagents and higher precision in the determi- nation of the end-point. Recently, these surfactant electrodes have been introduced commercially [2,3], facilitating surfactant determination in non-special- ized laboratories. In previous work, the development of all-solid state PVC membrane electrodes sensitive to anionic surfactants [4] was presented. This paper introduces the use of the developed membranes in tubular flow-through electrodes for flow-injection systems. In this way, the determination of anionic detergents becomes very fast and reproducible, thanks to the implicit advantages of the flow technique. Flow-injection systems have been applied to a large variety of fields, but there are few publications concerning the determination of surfactants. Nor- mally the described systems use liquid-liquid extrac- tion, with spectrophotometric detection [5,6] or 0003-2670/95/$09.50 0 199.5 Elsevier Science B.V. All rights reserved SSDI 0003-2670(94)00601-6