Studies of calcium ion-selective electrodes in the presence of biochemical materials

Abstract

Interferences by biochemical materials of responses towards calcium ions of calcium ion-selective electrodes have been studied for PVC matrix membrane electrodes based on calcium bis{di[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate} sensor with dioctyl phenylphosphonate (I), tripentyl phosphate (II) or trioctyl phosphate (III) as solvent mediator. Experiments have also been carried out on electrodes made from commercial calcium ion-selective electrode membranes based on an ionophore sensor (electrode IV). E. m.f. changes of <0.5 mV were observed for up to 10^–3M starch, sucrose, uric acid, creatinine and bilirubin. Larger e.m.f. changes were observed for cholic acid, cholesterol, lecithin and vitamin D₂(each of which were tested as solutions in ethanol or propan-1-ol added to the calcium ion containing solution in water or 0.15 M sodium chloride solution). Electrode III showed the greatest resistances to interferences by the biochemical components, followed by electrode IV. Interferences by urea and glucose were less than 1 mV for electrodes I-III and slightly more for electrode IV.