TM 5-6630-215-12
(b) The method of analysis used in the high range test is a
modification of the cadmium reduction method using gentistic acid in
place of 1-naphthyl amine.
The test registers both nitrates and
nitrites present in the water sample and eliminates the need for
dilutions by operating in the most usefull range.
All the necessary
reagents have been combined into a single stable powder called the
nitrate reagent.
(2) Nitrogen, Nitrate, Range 0-30 mg/l (figs. 2-11 and 2-12, and
para 2-18).
NOTE
The Nitrate reagent is slightly temperature
sensitive.
For best results, the test should be
performed with a sample temperature of 20° -
25°C (68° - 75°F).
A deposit of unoxidized metal will remain after
the Nitrate reagent powder has dissolved.
This
will have no effect on test results.
The extent of color development in the nitrate
nitrogen test using Nitrate reagent powder is
partially affected by the shaking time and
technique of the analyst.
For most accurate
results, the analyst should make successive tests
on a solution containing a known amount of
nitrate and adjust shaking time to obtain the
most accurate results.
(a) Take a water sample by filling a clean sample cell to the
25 ml mark.
(b) Add the contents of one nitrate reagent powder pillow to
the sample cell, stopper, and shake vigorously for exactly one minute.
An amber color will develop if nitrate nitrogen is present.
Allow at
least 5 minutes for proper color development but do not wait more than
15 minutes before completing steps (c) and (d).
(c) Fill another sample cell to the 25 mark with original
water sample and place it into the cell holder.
Insert the Nitrogen,
Nitrate meter scale into the meter and adjust the wavelength dial to
500 nm.
Adjust the light control for a meter reading of zero mg/l.
(d) Replace the blank sample, step (c) with the prepared sample
in the cell holder and read the mg/l nitrate nitrogen (N).
(e) The results can be expressed as mg/l nitrate (NO3) by
multiplying the mg/l nitrate nitrogen (N) by 4.4.
2-47
