Monday, November 5, 2007
90-13

Design of a Low-Cost, Flow-Through Electrical Conductivity Probe.

Charles Walker, Jack Watson, and Roderick Thomas. The Pennsylvania State University, 411 ASI Building, University Park, PA 16802

Application of a conservative tracer for chemical transport in soil columns is essential for the determination of a variety of sorption parameters. Tracers such as potassium chloride have been applied and measured in effluent fractions at the conclusion of the experiment. However, “real time” detection of the tracer would allow for more efficient sample collection during the study. Therefore, a low-cost, easy to fabricate, flow-through EC detector has been designed. Made out of Teflon, to reduce chemical adsorption, the funnel like device uses surface tension to hold approximately 0.1 mL of effluent. This design also can double as a drop counter to measure the approximate volume of effluent coming out of the column. Within the detection chamber, two stainless steel rods (1.5 mm in diameter) are used for electrodes. For the EC probe, the electrodes are attached to a simple electrical circuit and then monitored with a Campbell Scientific CR1000 Datalogger, using the AC half-bridge instruction. Calibration was performed using potassium chloride standards, which yielded a 2nd order polynomial regression with an r-squared value of 0.99. For the drop counter, the electrodes were directly attached to the Campbell Scientific CR1000 Datalogger and was measured using the pulse counting function within the datalogger. The EC probe and drop counter data will be compared with effluent column samples taken from a fraction collector.