Ion-selective electrode potentiometry in environmental analysis

This review will illustrate how it is possible to develop ion-selective electrode (ISE) methodologies that meet the stringent requirements (i.e., high selectivities and very low detection limits) for the analysis of important analytes in the environment, and will present a variety of examples on the application of ISEs in environmental analysis. Despite the experimental biases that have limited the analytical performance of ISEs through apparently high detection limits and modest selectivities, there has been a plethora of research in the application of ISEs in the monitoring of environmentally important trace metals and anions in natural waters and soils. Most popular has been the analysis of free metals in natural waters, as this parameter is known to be a master variable in the uptake and toxicology of trace metals on aquatic biota reflecting the bioavailability of trace metals in the environment. Furthermore, as copper is a major trace metal in coastal waters due to its extensive use in antifouling paints on sea vessels and structures, there are many reports in the literature on the use of the copper ISE in assays of either free copper or the copper complexing capacity of natural waters and soil peats. Moreover, there have been a variety of studies showing a strong correlation between free copper levels and the toxicity of copper on a variety of marine and fresh water organisms. Nevertheless, there are numerous reports in the literature that have used ISEs to monitor important anions such as fluoride phosphate, sulfate, nitrate, nitrite, chloride, cyanide, etc., as well as other important cations such as ammonium and chromium(VI) in waste and natural waters. In conclusion, this review will present new and interesting perspectives on the application of ISEs in environmental analysis using approaches such as real-time remote monitoring of water quality, shipboard monitoring of environmentally important analytes using flow analysis instrumentation, the use of robust all-solid-state ISEs in submersible instruments for long-term deployment in the field, and innovative analytical approaches such as backside calibration and switchtrodes that avoid standard addition analysis and the concomitant perturbation in analyte speciation in natural samples.