Abstract
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 μmol/L in 50 mmol/L 1,4-piperazinediethanesulfonic acid (PIPES) buffer. The method showed significant positive interference in plasma at pH <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 μmol 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 >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.
Original language | English (Ireland) |
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Pages (from-to) | 904-908 |
Number of pages | 5 |
Journal | Clinical Chemistry |
Volume | 38 |
Issue number | 6 |
DOIs | |
Publication status | Published - 1992 |
Keywords
- Analytical error
- Fibrinogen
- Monochromatic and bichromatic assays compared