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Merck

Extended sensitivity for the calcium selective electrode.

Analytical biochemistry (1986-09-01)
R W Morton, J K Chung, J L Miller, J P Charlton, R S Fager
ABSTRACT

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.

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Supelco
Dioctyl phenylphosphonate, Selectophore
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Supelco
hemi-Calcium bis[4-(1,1,3,3-tetramethylbutyl)phenyl] phosphate, Selectophore, ≥97.0%
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