Design and preliminary performance characteristics of a newly proposed reference cell for ionized calcium in serum.
A novel flow-through design for a calcium ion-selective liquid membrane and half-cell is proposed. The membrane is based on a neutral carrier for calcium and has the same quantitative chemical composition as that used in most commercial analyzers for ionized calcium (iCa2+). The membrane and half-cell follow the specifications in the Stage 1, Draft 4 document for a Reference Method for iCa2+ of the IFCC Expert Panel on pH, Blood Gases, and Electrolytes. Measurements of iCa2+ in serum with this cell confirm prior observations that protein adsorption on the membrane surface causes a rapid but reversible shift in the cell calibration signal and possible systematic errors in the measurement of iCa2+ in serum. When the protein adsorption phenomenon is maintained at equilibrium during calibrations and sample measurements, the new cell can be used to reproducibly assign iCa2+ concentrations to serum pools. These calibrated pools may then be used as reference materials and to resolve the biases known to exist among commercial iCa2+ analyzers.
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Ciba Corning Diagnostics Corp., Medfield, MA 02052.
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D002118:Calcium / Q000097:blood*; D002413:Cations, Divalent; D004566:Electrodes; D006801:Humans; D008567:Membranes, Artificial; D012015:Reference Standards
D002413:Cations, Divalent; D008567:Membranes, Artificial; D002118:Calcium