Recent advances in the field of light emitting diodes have enabled the production of new all solid-state fluorometers. High intensity light emitting diodes are used to excite the fluorophores and photocells are used to detect the emission. These fluorometers are small, with low power consumption, but they are highly sensitive with exceptional stability and low noise. The instruments are used in conjunction with water treatment chemicals that contain an inert fluorescent tracer. Handheld, battery-
powered units are used for grab sample analysis and provide greatly improved accuracy with less testing time for systems where chemical addition is controlled manually. On-line fluorometers can provide
continuous signals for a variety of automated control schemes. Important system diagnostics such as cycles of concentration and polymer recovery measurements are easily performed. The low cost and versatility of these units brings tracer technology to a broad range of facilities where it was previously not viable.