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Determination Of Serum Calcium By Means Of Orthocresolphthalein Complexone.
Published 1966 · Chemistry, Medicine
The use of orthocresolphthalein complexone (OCPC) as a reagent for the determination of calcium was introduced by Anderegg and associates and Schwarzenbach. Pollard and Martin and Stern and Lewis soon thereafter described manual spectrophotometric procedures using this dye. The procedure of Pollard and Martin is not applicable to the analysis of biologic materials. The method described by Stern and Lewis deals with the analysis of blood serum. Calcium is precipitated as the oxalate from 0.1 ml. of serum. The precipitate is washed and the oxalate ion, which in this procedure interferes with subsequent color development, is destroyed by heat (500 C. for 30 min). The calcium carbonate residue is dissolved in 0.1 ml. of N HC1, all traces of which must be removed by drying and heating before and residue is treated with a pH 8.5 borate-buffered OCPC color reagent. The absorbance is measured at 575 mju. Kessler and Wolfman have recently described an automated procedure adapted to the Autotechnicon. Our paper presents a greatly improved manual spectrophotometric method based upon release of the bound calcium by means of protein precipitation and the complete masking of the response of the dye to magnesium by means of 8-quinolinol (direct method). As a reference method, the calcium is precipitated as the oxalate. Without being washed, this is dissolved in 0.2 N HC1, an aliquot of which is reacted with the OCPC color reagent (alternate procedure).