Abstract
The potentiometric selectivities of two 14-crown-4 ethers incorporated in PVC membrane electrodes were determined for lithium with respect to sodium and potassium in different solvents and in different carrier solutions using flow injection analysis. Four methods for calculating selectivity coefficients were compared. A correlation is made between the relative levels of the interfering ion and primary ion and the numerical values of the selectivity coefficients calculated by the different methods. An increased level of sodium causes divergence among the values of the selectivity obtained by different methods, increases the selectivity of lithium over sodium, decreases the sensitivity and the slope of the calibration graph, and distorts the linearity of the curve.
