TOTAL AMMONIA MONITORING USING AN OPTRODE AND AN ELECTROCHEMICAL SAMPLE PH ADJUSTING SYSTEM

The gas permeable ammonia probe, in everyday use, has a lower limit of detection which does not satisfy the requirements of the Environmenta l Regulators, for natural waters investigations. The lower limit requi rement has been suggested as 25 mu g/l. PTFE membranes impregnated wit h dyes responsive to ammonia gas concentration changes have shown that limits of detection lower than those found using gas permeable probes are possible. Research and development was instigated by M Squared Te chnology to produce a system using a colour measurement technique and to try and reduce the cost of ownership of on-line systems. An optrode was developed to meet the requirements of the Regulators, and the res ults are described in this paper. Simultaneously with this development a method was found, and patented for changing the pH level of the sam ple, without the need for addition of reagents. This was developed in order to reduce maintenance and running costs on total ammonia monitor s. As the system was researched and developed, the findings led to fur ther patents being applied for, in the field of sample pH ''splitting' ', surface cleaning of sensors and pipe lines, and the prevention of h ardness precipitation when the pH of the sample had been elevated. The paper describes the findings and results of these developments. (C) 1 998 Published by Elsevier Science Ltd. All rights reserved.