LaMotte SMART Spectro Spectrophotometer - Manual (Page 181)

Nitrogen is essential for plant growth, but the presence of excessive amounts in
water supplies presents a major pollution problem. Nitrogen compounds may
enter water as nitrates or be converted to nitrates from agricultural fertilizers,
sewage, industrial and packing house wastes, drainage from livestock feeding
areas, farm manures and legumes. Nitrates in large amounts can cause “blue
babies” (methemoglobinemia) in infants less than six months of age. Nitrate
concentration is an important factor to be considered in livestock products,
where, in addition to causing methemoglobinemia, it is responsible for many
other problems. Nitrates in conjunction with phosphate stimulate the growth
of algae with all of the related difficulties associated with excessive algae
growth.
U.S. Public Health Service Drinking Water Standards state that 10 ppm
nitrate nitrogen should not be exceeded. To the sanitary and industrial
engineer, concentrations of less than 1 ppm are acceptable.
APPLICATION: Drinking, surface, saline, domestic and industrial waters.
RANGE: 0–25 mg/L Total Nitrogen
METHOD: All forms of nitrogen are converted to nitrate by an alkaline
persulfate digestion. Interference from halogen oxides is
eliminated by the addition of sodium metabisulfite. Nitrate
in acid reacts with chromotropic acid to form a yellow color
in proportion to the amount of nitrate in the treated sample.
SAMPLE
HANDLING AND
PRESERVATION: If the sample can not be analyzed immediately, the sample
should be preserved by adjusting the pH to 2 or less with
concentrated sulfuric acid and refrigerated at 4°C. Warm the
sample to room temperature and neutralize with 5.0 N
sodium hydroxide before analyzing.
INTERFERENCES: Bromide (>60 ppm) and chloride (>1000 ppm) will have a
positive interference.
Nitrogen, Total 2/4 SMART SPECTRO TEST PROCEDURES 05.04