Method 353.2

Nitrogen, Nitrate-Nitrite (Colorimetric, Automated, Cadmium Reduction)

This method pertains to the determination of nitrite singly, or nitrite and nitrate combined in surface and saline waters, and domestic and industrial wastes. The applicable range of this method is 0.05 to 10.0 mg/L nitrate-nitrite nitrogen. The range may be extended with sample dilution. A filtered sample is passed through a column containing granulated copper-cadmium to reduce nitrate to nitrite. The nitrite (that originally present plus reduced nitrate) is determined by diazotizing with sulfanilamide and coupling with N-(1-naphthyl)-thylenediamine dihydrochloride to form a highly colored azo dye which is measured colorimetrically. Separate, rather than combined nitrate-nitrite, values are readily obtained by carrying out the procedure first with, and then without, the Cu-Cd reduction step.

Method Data

Hold Times, Preservatives, Preps, Collection, Analytical & Documentation
Holding Time:	Analysis should be made as soon as possible. If storage is required, preserved samples are maintained at 4°C and may be held for up to 28 days. Samples to be analyzed for nitrate or nitrite only should be cooled to 4°C and analyzed within 48 hours.
Preservatives:	Samples must be preserved with sulfuric acid to a pH <2 and cooled to 4°C at the time of collection. When samples must be stored for more than 24 hours, they should be preserved with sulfuric acid (2 mL concentrated, per liter) and refrigeration.
Required Preps:	None noted in method.
Collection Method:	Grab; Samples should be collected in plastic or glass bottles.
Analytical Methodology:	Autoanalyzer; Colorimeter equipped with a 15 mm or 50 mm tubular flow cell and 540 nm filters.
Documentation:	353.2

* The analytes and detection limits listed for each method represent the typical detection limits and analytes reported for that particular method. Keep in mind that analyte lists may vary from laboratory to laboratory. Detection limits may also vary from lab to lab and are dependent upon the sample size, matrix, and any interferences that may be present in the sample.