Comparative study of tripodal oxa-amides and oxa-esters as ionophores in potentiometric ion-selective electrodes for alkali and alkaline earth cations (original) (raw)

1993, Analytica Chimica Acta

Two sets of oxa-amide and oxa-ester tripodal ligands have been prepared and evaluated as ionophores in PVC membrane electrodes for the analysis of Li+, Na+, K+, Ca*' and Mg *+ ions. The effects of the nature of the plasticiser bis(butylpentyl)adipate (BBPA) vs. o-nitrophenyl octyl ether (oNPOE), the structure of the ionophore, the pH and the ionic strength of the analyte solution on the electrode response were studied. The oxa-amides gave a superior performance (slope, limits of detection) than the oxa-esters particularly at higher ionic strengths, although super-Nernstian responses were observed with the more charge-dense ions in the presence of chloride and/or with the less polar plasticiser BBPA. Intracellular measurements of sodium concentration could be effected with a sensor based on bis (N,N',N"-tributy1~,4',4"-propy1dintris(3-oxabutanamide) and oNPOE for which -log KNyE = 2.64 and -log KNyM = 3.0, while bis(N,N',N"-tributyl)-2,2',2"-phenylmethylidintris(3-oxabutanamide) and oNPOE functioned as an effective calcium sensor with high selectivity over magnesium (-log KCa,Mg = 4.8).