Lifetime of liquid junction free reference electrodes with polymeric membranes as a function of lipophilicity and...

The equations allowing to estimate the lifetime of membrane liquid junction free reference electrodes (LJFREs) based on ionic liquids or lipophilic salts (hereinafter referred to as ionic components, IC) as a function of IC lipophilicity parameters, diffusion coefficients in the membrane and aqueous phases, membrane thickness and stirring conditions of the sample solution have been obtained. It follows from the obtained equations that, for highly lipophilic ICs, leaching from the membrane during operation depends rather on stirring conditions than on diffusion coefficients in the membrane phase. On the contrary, for moderately lipophilic ICs the diffusion in the membrane phase is the main factor that determines the lifetime of these LJFREs. Thus, lowering of diffusion coefficients seems to be promising for creating LJFREs based on moderately lipophilic ICs. The lifetimes of traditional and planar LJFREs, corresponding to a twofold decrease in IC concentration in the membrane phase, are estimated using the obtained equations. The results of the calculations are in good agreement with those obtained within the framework of the more rigorous interface equilibria-triggered dynamic diffusion model.