A novel potassium ion sensing based on Prussian blue thin films

A novel method for sensing potassium ions in aqueous solutions is presented . This method is based on the Prussian blue (PB) modified tin oxide (TO) el ectrode. Thin films of PB (KFeFe(CN)(6)), deposited onto transparent TO sub strate, are: reduced to Everitt's salt (ES, or K2FeFe(CN)(6)) in solutions containing potassium ions. Using an in situ measurement of the absorbance c hanges in PB thin film while applying different reductive potentials to the electrode, the PB mole fraction within the thin film, x, can be obtained f or solutions containing various concentrations of potassium ions. By applyi ng either the theory of regular solution (0.25 < x < 1) or the Margules equ ation (0 < x < 0.25) to the Nernst equation, one can construct a special fu nction, which depends mainly on the PB mole fraction and the interaction pa rameters involved. This sensing method, which eliminates the need for pre-c onditioning the electrode to a fixed potential, as proposed previously by o ther researchers, is based on a linear log-log plot of this special functio n against the potassium ion concentrations. Such a relationship was observe d when the K+ concentrations ranged from 3.3 x 10(-4) M to 1.0 M. The inter ferences of Na+ and Ba2+ on the K+ sensing are also studied. (C) 2001 Elsev ier Science B.V. All rights reserved.