Time-Dependent Phenomena in the Potential Response of Ion-Selective Electrodes Treated by the Nernst−Planck−Poisson Model. Part 2: Transmembrane Processes and Detection Limit

Abstract

The detection limit of ion-selective electrodes (ISEs) is of great interest because of the many possible practical applications of ISEs in trace analysis. Existing theoretical interpretations of the detection limit of ISEs are restricted by severe assumptions such as steady-state and electroneutrality, which hamper theorizing on this problem. For this reason, the Nernst-Planck-Poisson (NPP) equations are used to predict and visualize the detection limit variability under nonequilibrium conditions. For the first time, the NPP model is applied to the so-called inverse problem: finding the optimal measurement time and inner solution concentration for lowering the detection limit.

A solid-contact Pb2+-selective polymeric membrane electrode with Nafion-doped poly(pyrrole) as ion-to-electron transducer

“…Lead ionophore [IV tert-Butylcalix [4]arene-tetrakis(N,Ndimethylthioacetamide)], sodium trakis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB), 2-nitrophenyl octyl ether (o-NPOE), and high molecular weight poly(vinyl chloride) (PVC), tetradodecylammonium tetrakis-(4-chlorophenyl) borate (ETH500) were purchased from Fluka (Buchs, Switzerland). Nafion-perfluorinated resin solution (5 wt.% in a mixture of lower aliphatic alcohols and water) and pyrrole (98%) were obtained from Aldrich.…”

“…However, the conventional polymeric membrane electrodes with the inner filling solutions suffer from ion fluxes of primary ions between the inner aqueous solution and the sample solution, which may deteriorate the lower detection limits [3] and the selectivity coefficients of the ISEs [4]. Many empirical approaches have been used to decrease these ion fluxes including adjusting the composition of the inner solution [5,6], lowering the concentration of ionic sites, and increasing the thickness and polymer content of the membrane [7].…”

Modeling of Electrodiffusion Processes from Nano to Macro Scale

“…44. Ions entering the membrane are complexed at the boundaries, therefore not only the boundary fluxes of these ions, but also of their complexes, are taken into account.…”

Comparison of different approaches to the description of the detection limit of ion-selective electrodes

“…An approach, based upon this idea and dedicated to the general description of ISE behaviour, was later developed [6][7][8][9].…”

“…The first NPP model implementation where the method of lines (MOL) [11] was used was presented in [12,13]. Later on, MOL extensions of the NPP model for an arbitrary number of layers were developed and implemented in C++ [14] or in MathCad [9] and Matlab [15] scripts.…”