Direct photometric analysis of serum calcium with glyoxal bis (2-hydroxyanil

A spectrophotometric method for the direct determination of microgram quantities of calcium in serum is presented. In this procedure, 0.02 ml. of serum is interacted with buffered glyoxal bis (2-hydroxyanil) solution (GBHA) at pH 12.6. The resultant red calcium-GBHA complex is diluted in methanol-acetone-water solution, and the absorbance determined at 520 m. The effects of pH, temperature, CBHA concen-tration, and alcohol-water ratio were evaluated, as was interference by serum con-stituents. The method is simple and precise, and the analytical results compare well with the chloranilate procedure for serum calcium. THE PREPARATION of glyoxal bis (2-hydroxyanil) solution (GBHA) and its interaction with various metals to form colored salts was first re-ported by Bayer (1). This reagent was proposed as a sensitive qualita-tive test for calcium by Goldstein and Stark-Mayer (2), since micro-gram quantities form a bright red color in alkaline solution. Subse-quently, quantitative pilotometric procedures, based on the prior ex-traction of the calcium-GBHA complex with organic solvents, wer