Standard stock solution— Dissolve about 815mg of potassium nitrate in 500mLof water,and mix.

Standard solution— Dilute 1mLof the Standard stock solutionwith water to 10mL,and mix.Dilute 1mLof this solution with water to 50mLto obtain a solution containing 2ppm of nitrate.

Test solution— Transfer 5g of Adipic Acid to a 50-mLvolumetric flask.Dissolve in water,with heating,and dilute with water to volume.Allow to cool and crystallize,then pass through a sintered-glass filter.Wash the filter with water,and collect the filtrate and washings until a volume of 50mLis obtained.[NOTE—This solution is to be used in the tests for Chloride,Sulfate,Iron,and Heavy metals.]

Procedure— To 1.0mLof the Test solutionand to 1.5mLof the Standard solution,separately add 2mLof concentrated ammonia,0.5mLof manganese sulfate solution (1in 100),and 1mLof sulfanilamide solution (1in 100),and dilute with water to 20mL.Add 100mg of zinc powder,and cool in an ice bath for 30minutes,shaking periodically.Filter 10mLof the solution,cool in an ice bath,and then add 2.5mLof hydrochloric acid and 1mLof a naphthylethylenediamine dihydrochloride solution (1in 100).Allow to stand at room temperature for 15minutes:the color of the Test solutionis not darker than a concomitantly prepared Standard solution;the limit is 0.003%.The test is invalid if a concomitantly prepared blank solution (prepared using 1mLof water instead of 1mLof the Test solution)is darker than a solution containing 2mg of potassium permanganate per L.