202 METHODS FOR THE ANALYSIS OF BLOOD 



PLASMA CHLORIDES 



Method of Van Slyke and Donleavy l 



Principle. Precipitation of the proteins* and titration of the 

 chlorides with a standard potassium iodide solution. 



Procedure. Two c.c. of oxalate or citrate plasma are drawn 

 into a dry pipette calibrated to contain 2 0.005 c.c. (the pipette 

 must weigh 1.9940.005 gm. more when rilled with water at 20 

 than when empty and dry). The plasma is run into a 50 c.c. 

 measuring flask half full of water, and the pipette is rinsed by 

 drawing the water up into it twice. Ten c.c. of the standard 

 silver nitrate-picric acid solution are added, and the mixture is 

 diluted to the 50 c.c. mark and shaken at intervals for several 

 minutes until coagulation is complete. The addition of a drop 

 or two of caprylic alcohol prevents foaming and facilitates coagula- 

 tion. The solution is passed through a dry, chloride-free filter, 

 the first portion of filtrate being passed through, if necessary, a 

 second time to remove turbidity completely. Twenty c.c. dupli- 

 cate portions of the filtrate are measured with a calibrated pipette 

 into 100 c.c. Erlenmeyer flasks, 4 c.c. of the starch-citrate indicator 

 solution are added to each, and the standard KI is run in from a 

 burette until a permanant blue end-point is reached. 



If it is desirable to use less than 2 c.c. of plasma, 1 c.c. measured 

 within 0.002 c.c. may be precipitated with 5 c.c. of the stand- 

 ard silver solution and diluted to 25 instead of 50 c.c., the filtrate 

 yielding only one 20 c.c. portion instead of duplicates. 



The End-point. Only a permanent and unmistakable blue is 

 taken as the end-point. If the iodide is run in rapidly near the end 

 of the titration, iodine may be formed more rapidly than silver 

 nitrate precipitates it, and a false end-point reached which dis- 

 appears after a few seconds shaking. If, toward the end of the 

 titration, the iodide is added slowly the blue shade caused by each 

 drop disappears as soon as the solution is rotated, until the genuine 

 end-point is reached. The latter is permanent, and in fact deepens 

 with time. 



Standard Solutions. 1. Silver Nitrate Solution. An acid 

 M/29.25 solution of silver nitrate, 1 c.c. of which is equivalent to 

 2 mg. of NaCl. 



1 Van Slyke and Donleavy: Jour. Biol. Chem., 1919, 37, 551. 



