Due the high temperature and pressure conditions found in geothermal wells, tracer studies designed to elucidate properties of geothermal reservoirs are traditionally conducted by pulling liquid samples from the wellhead. These samples are then sent off for analysis in a fixed laboratory setting. Unfortunately by pulling the sample from the surface, information regarding the depth of the fractures generating the tracer flow is lost. Additionally, significant time is lost in sending the samples off for traditional chemical analysis. This presentation focuses on our efforts to develop downhole high temperature and pressure stable ion selective electrodes capable of measuring the concentration of tracers used in geothermal studies, along with pH, at various depths in the wellbore creating tracer concentration and pH depth profiles for use in geothermal reservoir analysis.