Optimization of an electrolyte conductivity detector for measuring low ion concentrations

The optimization process of a planar interdigitated conductivity detector for measuring very low electrolyte concentrations for use in a lab-on-chip gas detection system is described. An electrical equivalent of the sensor is given, which includes the double layer capacitance dependency on the electrolyte concentration, resulting in a better description of the impedance of the sensor. The cell constant of the sensor is minimized to reduce the cell resistance in low specific conductivity solutions under the restriction of a small electrode area (less than or equal to 0.1 cm(2)) for fast measurement, prescribed by the ammonia detection system. The small size makes it suitable for integration in micro channels. The developed sensor has a cell constant of 7.9 m(-1) resulting in a maximum resistance for deionized water of 177 kOmega at a frequency of 1 kHz.