Instrumentation and Procedures for Long-Term Automated Monitoring of Metal Ions in Industrial Effluents by Liquid Chromatography with Electrochemical Detection

This chapter discusses the complete automation of liquid chromatography with an electrochemical detection method using instrumentation. The continual monitoring of metal ions in industrial effluents is undertaken for seven day periods without operator intervention. Diethyldithiocarbamate or pyrrolidinedithiocarbamate complexes of metal ions are prepared automatically in a reactor coil, using a low pressure pumping systems which mix the industrial effluent and an acetonitrile solution containing the dithiocarbamate ligand. The acetonitrile-water solvent mixture formed in the complex preparation stage is then used as the solvent medium for the chromatographic separation of the metal dithiocarbamate complexes via the use of a high pressure pump. Electrochemical detection at a glassy carbon electrode is achieved by oxidation of the metal complex or ligand attached to the metal. After extensive experience with this automated system it is recognized that deficiencies in the completely automated procedure arise from the slow decomposition of the dithiocarbamate ligand over the seven day operation period, the necessary presence of excess electroactive dithiocarbamate ligand which has to be removed prior to electrochemical detection by an anion exchange column, and the use of the relatively expensive and toxic acetonitrile solvent required for the preparation of the water insoluble dithiocarbamate complexes.