A Study of the Estimation of Chloride in Blood and Serum

Many modifications have been suggested for the determination of chloride in blood and other body fluids. The simplest and most thoroughly studied is a method proposed by Van Slyke (1) involving ashing of serum with concentrated nitric acid in the presence of silver nitrate to prevent volatilization of the chloride. In making a preliminary study of Van Slyke’s method before using it for a series of analyses, we attempted to cut down the period of digestion (2 hours on a water bath) by boiling the mixture gently over a micro burner until the solution was clear. When this was done it was noted that the results tended to be higher than those obtained by the regular Van Slyke procedure. The silver nitrate in nitric acid used by Van Slyke forms an immediate voluminous precipitate, protein and silver chloride, when added to serum. In order to diminish the possibility of occlusion of chloride or silver, it was thought that the reagents might better be added separately. Aqueous silver nitrate was therefore prepared. It was made 3 times as strong as Van Slyke’s standard so that the total volume of the solution could be kept small. The procedure used was: 1 cc. of serum was measured into a large test-tube (approximately 25 X 200 mm.), 1 cc. of the standard aqueous silver nitrate solution added, and the tube shaken; then 3 cc. of concentrated nitric acid were introduced, and, after being mixed, the contents were digested. Some digestions were carried out by heating the tubes in a boiling water bath for 2 hours and others by boiling the solutions gently over a micro burner for 15 to 20 minutes. After a few determinations were carried out and good results obtained, a series of comparisons was made with (1)