Prussian Blue (PB) is an excellent material as a sensor for electroinactive cations because of its electrochemical behavior and its zeolytic character. A simple 3-h laboratory designed for a quantitative analysis or an instrumental methods course is reported. This laboratory studies the transport of various cations into a PB-modified electrode upon reduction. Cyclic voltammograms are used to monitor the transport of ions such as K[superscript +] and Rb [superscript +] and observe the exclusion of Na [superscript +] and Mg [superscript 2+] ions. The ability for cations to enter the PB film is a function of the hydrated radius of the cations being analyzed.