LaMotte SMART Spectro Spectrophotometer User Manual

Page 201

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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

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