Direct potentiometric information on total ionic concentrations

Analytical Chemistry
A CeresaEric Bakker


Polymeric membrane ion-selective electrodes exhibit an apparently super-Nernstian response at low sample activities if inner solutions are used that induce strong zero-current fluxes of primary ions toward the inner compartment. This is due to the limited ion fluxes in the aqueous boundary layer near the membrane. In the presence of labile complexes, the effective flux rate is increased and the emf depends on the total concentration of the ions. The concept is illustrated experimentally with calcium-selective electrodes based on the ionophore N,N-dicyclohexyl-N',N'-dioctadecyl-3-oxapentanediamide (ETH 5234) that either respond to total or free ion concentrations. Samples can be distinguished that contain varying levels of total calcium but are all buffered with EDTA to the same free calcium concentration of 5 x 10(-8) M.


Aug 15, 2002·Analytical Chemistry·Eric Bakker, E Pretsch
Apr 5, 2003·Analytical Sciences : the International Journal of the Japan Society for Analytical Chemistry·Wagiha H Mahmoud
Feb 14, 2009·Chemical Communications : Chem Comm·Jiawang Ding, Wei Qin

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