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.