NSWC/WOL/TR 75-35 



The above method will give better than 90% conversion of the 

 sample nitrate. It is recommended that a recovery study be used to 

 determine the conversion efficiency in the type of sample being 

 measured . 



4.3.2.4 Chloride 



Two methods are presented for the determination of chlorides. 

 The colorimetric method is suitable for use in clear samples with 

 relatively low chloride concentration, and the potent iometric method 

 is suitable for colored or turbid samples with high chloride 

 concentrat ion . 



In the colorimetric method, chloride is determined by reacting 

 the sample with mercuric thiocyanate which forms unionized mercuric 

 chloride and thiocyanate ions. The thiocyanate is reacted with 

 ferric ion producing highly colored ferric thiocyanate proportional 

 to the chloride in the original sample. 



2C1" + Hg(SCN) 2 — *-HgCl 2 + 2SCN~ H±± — „Fe(SCN) +2 



The color intensity is then measured with a spectrophotometer at a 

 wavelength of 480 mm. There are no significant interferences in the 

 analysis . 



In the potent iometric method, chloride is determined by 

 potent iometric titration with silver nitrate solution using a glass 

 and silver-silver chloride electrode system. During titration, an 

 electronic voltmeter is used to detect the change in potential 

 between the two electrodes. The end point of the titration is that 

 instrument reading at which the greatest change in voltage has 

 occurred for a small and constant increment of silver nitrate added. 



Ferric ion interferes if present in an amount that is 

 substantially higher than the amount of chloride. Chromic ion, 

 ferrous iron, and phosphate do not interfere. Iodide and bromide 

 also are titrated as chloride. 



Grossly contaminated samples usually require pre-treatment . 

 Where contamination is minor, some contaminants can be destroyed 

 simply by the addition of nitric acid. 



53 



