Extended sensitivity for the calcium selective electrode

✍ Scribed by Richard W. Morton; Jun Ki Chung; James L. Miller; J.Paul Charlton; Roger S. Fager

• Book ID: 102987544
• Publisher: Elsevier Science
• Year: 1986
• Tongue: English
• Weight: 605 KB
• Volume: 157
• Category: Article
• ISSN: 0003-2697
• DOI: 10.1016/0003-2697(86)90636-6

✦ Synopsis

Sensitivity of calcium-selective electrodes heretofore has been limited to calcium concentrations above 10(-8) M in the absence of competing ions. We describe the use of calcium buffers to stabilize the free calcium in the reference electrode. Electrode calibration is linear to 10(-8) M and is curvilinear to 10(-11) M in the presence of 0.1 M ionic strength. Selectivity with respect to competing cations, magnesium, potassium, sodium, and hydrogen is preserved. Electrode response time is less than 2 s for small changes in calcium activity. Response range is linear over 9 log units of calcium activity. Potential-time stability is less than 10 mV/h at saturation currents. Although the silver-silver chloride terminals are photosensitive throughout the visible and near-ultraviolet regions, housing the reference and indifferent in opaque barrels avoids false photovoltaic response.