Measurement of ionized calcium in biological fluids

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Abstract
Three methods are described for the determination of ionized calcium in plasma ultrafiltrates and urine involving spectrophotometry, potentiometry and a computer calculation procedure. Good agreement between all three methods is demonstrated. The percentage of ionized calcium in plasma ultrafiltrates is about 89% at 25° and 83% at 37°. In urine about 50% of the total calcium is in the ionized form, the remainder being accounted for in terms of soluble complexes with citrate, phosphate, sulphate and oxalate ions.