N2 28.01

Nitrogen [7727-37-9].
» Nitrogen contains not less than 99.0 percent, by volume, of N2.
Packaging and storage— Preserve in cylinders.
Identification— The flame of a burning wood splinter is extinguished when inserted into a test tube filled with Nitrogen. [note—Exercise caution.]
Odor— Carefully open the container valve to produce a moderate flow of gas. Do not direct the gas stream toward the face, but deflect a portion of the stream toward the nose: no appreciable odor is discernible.
note—Reduce the container pressure by means of a regulator. Measure the gases with a gas volume meter downstream from the detector tube in order to minimize contamination or change of the specimens.
Carbon monoxide— Pass 1000 ± 50 mL through a carbon monoxide detector tube (see under Reagents in the section Reagents, Indicators, and Solutions) at the rate specified for the tube: the indicator change corresponds to not more than 0.001%.
Limit of oxygen— Not more than 1.0% of oxygen is present, determined as directed in the Assay.
Assay— Introduce a specimen of Nitrogen into a gas chromatograph by means of a gas sampling valve. Select the operating conditions of the gas chromatograph such that the standard peak signal resulting from the following procedure corresponds to not less than 70% of the full-scale reading. Preferably, use an apparatus corresponding to the general type in which the column is 3 m in length and 4 mm in inside diameter and is packed with a molecular sieve prepared from a synthetic alkali-metal aluminosilicate capable of absorbing molecules having diameters of up to 0.5 nm, which permit complete separation of oxygen from nitrogen. Use industrial grade helium (99.99%) as the carrier gas, with a thermal-conductivity detector, and control the column temperature: the peak response produced by the assay specimen exhibits a retention time corresponding to that produced by an oxygen-helium certified standard (see under Reagents in the section Reagents, Indicators, and Solutions), and is equivalent to not more than 1.0% of oxygen when compared to the peak response of the oxygen-helium certified standard, indicating not less than 99.0%, by volume, of N2.
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Monograph Kahkashan Zaidi, Ph.D.
Senior Scientist
(AER05) Aerosols05
USP32–NF27 Page 1288
Pharmacopeial Forum: Volume No. 31(4) Page 1145