CONTINUOUS-FLOW SYSTEM FOR ON LINE WATER MONITORING USING BACK SIDE CONTACT ISFET-BASED SENSORS

A multiparametric continuous-now system for on-line monitoring of wate r based on ISFET sensors is described. The ISFETs used have silicon ni tride as gate material, and the electrical contacts are placed on the back side of the chip. This is a technological improvement that allows for a more compact ISFET packaging and greatly increases the lifetime of the sensor compared with planar type ISFETs, since the electrical parts are separated from the chemical environment. A special probe has been designed in order to encapsulate and apply these ISFETs into the now system, Further, a reference electrode based on standard Ag/AgCl technology has been constructed according to the ISFET probe design in order to integrate both sensors in the same flow-through cell. These probes can be easily replaced in the now system and are made of cheap and easily mechanized materials. Using these flow-through sensors, a c ontinuous-now system for the determination of pH, NH4+, Ca2+, and NO3- in waters has been designed, The system configuration is based on a m odular design (one setup for each parameter and a common sampling chan nel), which allows simple manipulation and maintenance as well as a go od flexibility for different analytical requirements, A study of the s ystem characteristics was performed by following the specifications fo r water monitoring, Under the conditions established for the flow syst em, a sampling rate of 20 h(-1) was obtained for each parameter, and l ong term stabilities of at least 3 weeks of daily work for ISFET senso rs and 5 months for the reference electrode have been achieved, The re sponse performances obtained show the feasibility of the BSC ISFET pro be use in continuous-now monitoring.