Determination of Serum Total Base

Abstract

Practically all the modern methods of determining serum total base are modifications of Fiske's 1 procedure for total base in urine. The modification proposed by Stadie and Ross 2 has until recently received the widest use. In this method, the serum is ashed directly without removal of phosphate, and the base in the ash, which is present as sulfate, is analyzed by the indirect titration method of determining the sulfate as benzidine sulfate. A correction is added for the amount of base present as metaphosphate.

Recently Peters and Van Slyke 3 have published a method combining the procedures of Fiske and of Stadie and Ross. The objection to the original method of Stadie and Ross is chiefly that the results obtained are too low and too variable because sulfates are not completely precipitated in the presence of phosphate and because the method of correcting for base bound to phosphate by adding the number of milliequivalents of inorganic phosphate in the serum is not accurate. Peters and Van Slyke's procedure avoids this difficulty by a preliminary removal of the phosphate as ferric phosphate by addition of ferric alum and then ammonia to precipitate the excess iron. In the author's experience, Peters and Van Slyke's method has a number of objectionable features. First, the procedure is tedious and time-consuming. As described, a single determination requires 24 hours or longer. Secondly, the technique is so difficult and so liable to errors by loss of material that it could not be entrusted to the average hospital technician. Thirdly, the blank is high and variable. Finally, an error is produced by a precipitation of from 1 to 2 m.eq. of calcium along with the ferric phosphate and ferric hydroxide.