LaMotte SMART Spectro Spectrophotometer - Manual (Page 201)

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
diffi culties 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
MDL: 2 mg/L
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
metabisulfi te. 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
& 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 SMART Spectro Test Procedures 2.11
Test P
rocedures