LaMotte SMART Spectro Spectrophotometer - Manual (Page 173)

APPLICATION: Drinking, surface, and saline waters; domestic and industrial
waters.
RANGE: 0.00–3.00 ppm Nitrate Nitrogen
METHOD: Powdered cadmium is used to reduce nitrate to nitrite. The
nitrite that is originally present plus reduced nitrate is
determined by diazotization of sulfanilamide and nitrite
followed by coupling with N-(1 naphthyl)-ethylenediamine
dihydrochloride to form a highly colored azo dye which is
measured colorimetrically.
SAMPLE
HANDLING &
PRESERVATION: Analysis should be made as soon as possible. If analysis
cannot be made within 24 hours, the sample should be
preserved by refrigeration at 4°C. When samples must be
stored for more than 24 hours, they can be preserved by
adding 2 mL of concentrated sulfuric acid per liter of sample.
For best results, the analysis for nitrate should be determined
at temperatures between 20°C and 25°C.
INTERFERENCES: Nitrite interferes at all levels. Strong oxidizing and reducing
substances interfere. Low results might be obtained for
samples that contain high concentrations of iron and copper.
Nitrate-Nitrogen–LR 2/3 SMART SPECTRO TEST PROCEDURES 04.08