Fluorimetric determination of calcium in serum with calcein blue

Abstract

Calcium was determined in serum by fluorimetry with calcein blue (CB) in a strongly alkaline solution (0.1 M KOH). Triethanolamine and N-(2-hydroxyethyl)iminodiacetic acid were used to mask iron, copper, zinc and magnesium. The relative standard deviation of the slope of a typical working curve was 0.45%. This value corresponds to confidence limits of 3.53 ± 0.02 at the 95% level. The correlation coefficient was 0.9999. The mean value of calcium in a 20-µl sample of Quality Control Serum was within the appropriate limits of the reference sample. The changes in the structure of CB on standing at high pH are discussed.