Potentiometric sensors for trace-level analysis.

This review summarizes recent progress in the development and application of potentiometric sensors with limits of detection (LODs) in the range 10(-8)-10(-11) M. These LODs relate to total sample concentrations and are defined according to a definition unique to potentiometric sensors. LODs calculated according to traditional protocols (three times the standard deviation of the noise) yield values that are two orders of magnitude lower. We are targeting this article at analytical chemists who are non-specialists in the development of such sensors so that this technology may be adopted by a growing number of research groups to solve real-world analytical problems.We discuss the unique response features of potentiometric sensors and compare them to other analytical techniques, emphasizing that the choice of the method must depend on the problem of interest. We discuss recent directions in sensor design and development and present a list of 23 sensors with low LODs, with references. We give recent examples where potentiometric sensors have been used to solve trace-level analytical problems, including the speciation of lead and copper ions in drinking water, the measurement of free copper in sea water, and the uptake of cadmium ions by plant roots as a function of their speciation.