A Photo-Cured Calcium Ion-Selective Electrode for Use in Flow Injection Potentiometry that Tolerates High Perchlorate Levels

An improved photo-cured membrane selective to calcium was developed based on the calcium bis[4-(1,1,3,3-tetramethylbutyl)phenyl] phosphate ionophore and incorporates the lipophilic additive, potassium tetrakis(p-chlorophenyl)borate. The calcium electrode exhibited a hyper-Nernstian response of 31.0 mV change per activity decade and a log-linear range between 1 × 10-5 to 0.1 M in pure calcium chloride solution, in steady-state mode. The calcium electrode was fast responding, reaching 90% of steady-state value in 5 s making it ideal for flow injection measurements. The photo-cured electrode can measure calcium in a high perchlorate background, and was used to determine the total calcium level in full cream milk that was digested by a nitric/perchloric acid mixture. The results obtained were in good agreement with atomic absorption spectroscopy measurements.