LaMotte SMART3 Colorimeter - Manual (Page 220)

APPLICATION: This method determines nitrate levels in drinking,
surface, saline waters, domestic and industrial waters.
RANGE: 0.00–3.00 ppm Nitrate Nitrogen
MDL: 0.10 ppm
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, Low Range SMART3 Test Procedures 11.10
Test P
rocedures