The Q45H/79 monitor is an on-line automated chemistry system that provides the components necessary to continuously perform total residual chlorine measurement. In operation, a small amount of the sample is pumped into the system and mixed with a pH 4 buffer and the with potassium iodide. Many on-line monitors for total residual chlorine use the iodometric method for measurement, where current between two exposed electrides determines the iodine concentration. ATI’s Model Q45H/79 Total Residual Chlorine Monitor uses this same standard iodometric method, but with a membraned sensor for measuring the iodine in the solution. The system takes the reacted sample containing iodine and uses a membraned amperometric sensor rather than exposed electrodes.