DETERMINATION OF MONOCHLOROACETIC ACID USING A FLOW-INJECTION SYSTEM FEATURING A FLOW-THROUGH ION-SELECTIVE ELECTRODE AND AN ION-EXCHANGE COLUMN FOR THE MINIMIZATION OF INTERFERENCE BY CHLORIDE

An automated flow injection system for on-line monitoring of monochlor oacetic acid (MCAA) in industrial processes for the production of zwit terionic surfactants (betaines) is developed, which can treat samples with chloride ion concentration up to I M. The system features an ion- exchange column for the separation of MCAA from the interferents in th e complex sample. The sample is injected at low pH values so that inte rfering anions, mainly chloride, are retained in the ion exchange colu mn. Detection is performed using specially constructed all-solid-state tubular flow-through ion selective electrodes sensitive to monochloro acetate. Selectivity data of the constructed electrodes are given, whi le their pH working range is 4.0-11.0 and their lifetime is greater th an 30 days through a range between 10(-4)-10(-1) M. Once applied to th e treatment of real samples, the system developed can detect MCAA in t he range between 5.10(-3)-10(-1) M, with a maximum deviation of 5% whe n compared to standard photometric methods of analysis. The short time used in each determination (30 s) in addition to its simplicity, lead s to an improvement of the techniques of analysis used until now. (C) 1998 Elsevier Science B.V.