Hach DR/700 Procedures Manual page 613

NITROGEN, MONOCHLORAMINE,
continued
SAMPLING AND STORAGE
Collect samples in clean plastic or glass bottles. Most reliable results
are obtained when samples are analyzed as soon as possible after
collection.
ACCURACY CHECK
Dilution water is required when testing a diluted sample and when
preparing standard solutions. Dilution water must be free of ammonia,
chlorine and chlorine demand. A convenient source is a recirculating,
deionizer system with carbon filtration which produces 18 megaohm-cm
water.
Standard Additions Method
a) Measure 50 mL of sample into three 50-mL mixing cylinders.
b) Use the TenSette Pipet to add 0.3, 0.6, and 1.0 mL of Nitrogen
Ammonia Standard, 10 mg/L as NH N to the three samples. Mix well.
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c) Analyze each sample as described above. The ammonia nitrogen
concentration should increase 0.06, 0.12 and 0.20 mg/L, respectively.
d) If these increases do not occur, see Standard Additions (Section I) for
more information.
Standard Solution Method
Prepare a 0.50 mg/L ammonia nitrogen standard by diluting 5.00 mL of
the Nitrogen Ammonia Standard Solution (as NH -N), 10 mg/L, to 100
3
mL with demineralized water. Or, using the TenSette Pipet, prepare a
0.50 mg/L ammonia nitrogen standard by diluting 1.0 mL of an
Ammonia Nitrogen Voluette Standard Solution, 50 mg/L as NH N, to
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3
100 mL with demineralized water.
STATISTICAL EVALUATION
A single operator repetitively tested samples of two laboratory prepared
solutions, using one DR/700, matched sample cells and two
representative lots of testing reagents. Testing 0.2 mg/L NH as N
3
concentration samples, the standard deviation was ±0.010 mg/L NH
.
3
Testing zero concentration samples, the limit of detection was 0.009 mg/L
NH . The limit of detection was calculated as three times the standard
3
deviation when testing zero concentration samples (Adapted from
Analytical Chemistry,1980, 52, 2242-2249).
CALIBRATION
The test procedure may be used with a User-Programmed method and
any 610-nm module. Perform Section 2.2.4.2, Calibration Using a
Relative Absorbance with One Standard, in the DR/700 Instrument
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