A FLOW-INJECTION APPROACH TO THE CONTINUOUS MONITORING OF RESIDUAL COAGULANTS (ALUMINUM AND IRON) IN POTABLE AND TREATED WATERS

An automated flow-injection analyser for the on-line monitoring of dissolved monomeric aluminium and dissolved iron in potable and treated waters is described. The aluminium method is based on complexation with pyrocatechol violet (PCV) and the iron method is based on the complexation with ferene S. The limits of detection using a solid-state light emitting diode - photodiode flow through detector - were 13 and 11 mug l-1 for aluminium and iron, respectively, and the linear range for both was 0-1000 mug l-1. Improvements to the monitor design of a previously reported system include a new computer system and detector modifications for increased sensitivity. The monitor performance met all the required industry specifications, e.g. for accuracy and precision and was > 98% reliable during on-line trials.