Photometric Determination of Total Nitrogen in Water with Phenol Disulfonic Acid as Color Reagent

In the photometric determination of total nitrogen in water with phenol disulfonic acid as color reagent,a modification of the sample digestion with alkaline potassium persulfate was made by carrying out the digestion in a pressurized reaction kettle instead of in a colorimetric tube,to avoid incomplete sample digestion,incomplete decomposition of the oxidant and loss of ammonia by evolution.Linear relationship was kept between values of absorbance and concentration of total nitrogen in the range of 0.02-1.90 mg·L-1.Detection limit (3σ) of the method found was 0.02 mg·L-1.Six water samples were analyzed by the proposed method,values of RSD′s (n=6) found were less than 3.5%.Test for recovery was made by standard addition method,giving results in the range of 98%-102%.