An improved method for the automated determination of urine calcium.
The problems of accurately determining urine calcium are described. The basic technique described is little changed from that originally used by Clark and Collip but the pitfalls encountered when applying this to automated procedures are demonstrated and a means of overcoming them proposed.
THE EFFECT OF HYDROGEN ION CONCENTRATION UPON THE DETERMINATION OF CALCIUM
McCrudden’s (1, 2) method has come to be recognized as the best for the accurate determination of calcium. The method is to precipitate the calcium as oxalate in the presence of sufficient ammonium chloride to hold the magnesium oxalate in solution, and of sufficient acid to hold the calcium oxalate partly in solution. Sodium acetate is then added to decrease the acidity and to precipitate the rest of the calcium oxalate on the crystals already formed. Thus, large crystals are made which are easy to filter and are not contaminated with occluded magnesium or calcium ph0sphate.l The amount of acetate is selected so as to give a solution not acid enough to dissolve the calcium oxalate, nor alkaline enough, if cold, to allow calcium phosphate to precipitate. These directions are empiric and must be followed accurately, as the author cautions2 Just what determines the amount of acetate is not definite, for he states that in the ash of feces 15 instead of 8 cc. are required.3 The sodium acetate added regulates the acidity of the solution. Unfortunately, at the time McCrudden wrote his article, Sbrensen’s (3), Michaelis’ (4), and Clark’s (5) monographs on hydrogen ion concentration were not published. In 1913, Hildebrand (6) of the Bureau of Standards showed the necessity of a systematic investigation of analytical methods with regard to the hydrogen ion concentration. Such information is not as yet available for
AUTOMATED FLUOROMETRIC METHOD FOR DETERMINATION OF SERUM CALCIUM.
A simple, rapid, accurate, and reproducible method for serum calcium has been developed utilizing a fully automated fluorometric system and fluorescein-complexone as the fluorophore. The results obtained agree with those obtained with the Clark-Collip permanganate titration.