arsenazo-iii and Hemolysis

We describe a method based on a single stable reagent for the determination of calcium in serum and plasma with use of Arsenazo III, 200 mumol/L in 50 mmol/L 1,4-piperazinediethanesulfonic acid (PIPES) buffer. The method showed significant positive interference in plasma at pH less than 6.6 because of the precipitation of fibrinogen, which was eliminated by increasing the pH to 6.8. The assay showed no interference from as much as 600 mumol of bilirubin and 12 g of hemoglobin per liter when applied in a simple monochromatic procedure at 660 nm. The standard curve for calcium was linear from 0 to 5.0 mmol/L. Addition of Intralipid at concentrations greater than 3 g/L demonstrated positive interference, which could be eliminated by using a 700-nm blanking wavelength. The procedure showed good agreement with all-method mean values from two external quality-control schemes.

Topics: Arsenazo III; Bilirubin; Calcium; Drug Stability; Fat Emulsions, Intravenous; Hemolysis; Humans; Hydrogen-Ion Concentration; Indicators and Reagents; Photometry; Quality Control

Topics: Adenosine Triphosphate; Arsenazo III; Azo Compounds; Calcium; Erythrocyte Membrane; Hemolysis; Humans; In Vitro Techniques; Spectrophotometry, Infrared