Nitrogen
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
N₂ 28.01
Nitrogen CAS RN®: 7727-37-9.
1 DEFINITION
Nitrogen contains NLT 99.0%, by volume, of nitrogen (N₂).
2 IDENTIFICATION
A. The flame of a burning wood splinter is extinguished when inserted into a test tube filled with Nitrogen. [Note-Exercise caution.]
3 ASSAY
3.1 Procedure
Sample: Nitrogen
Standard: Oxygen–helium certified standard (see Reagents, Indicators, and Solutions)
Chromatographic system
- (See Chromatography 〈621〉, System Suitability.)
- Mode: GC
- Detector: Thermal conductivity
- Column: 3-m length × 4-mm inside diameter: molecular sieve prepared from a synthetic alkali-metal aluminosilicate capable of absorbing molecules having diameters of up to 0.5 nm and completely separating oxygen from nitrogen
- Carrier gas: Helium (99.99%)
- Temperature: Thermostatically controlled
Analysis
Samples: Standard and Sample
Introduce the Samples separately into the gas chromatograph by means of a gas sampling valve.
Acceptance criteria: The peak response produced by the Sample exhibits a retention time corresponding to that produced by the Standard and is equivalent to NMT 1.0% of oxygen when compared to the peak response of the Standard, indicating NLT 99.0%, by volume, of N₂.
4 SPECIFIC TESTS
[Note-Reduce the container pressure by means of a regulator. Measure the gases with a gas volume meter downstream from the detector tube to minimize contamination or change of the specimens.]
4.1 Carbon Monoxide
Sample: 1000 ± 50 mL
Analysis: Pass the Sample through a carbon monoxide detector tube (see Reagents, Indicators, and Solutions) at the rate specified for the tube.
Acceptance criteria: NMT 10 ppm
4.2 Limit of Oxygen
Analysis: Determined as directed in the Assay
Acceptance criteria: NMT 1.0%
4.3 Odor
Analysis: 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.
Acceptance criteria: No appreciable odor is discernible.
5 ADDITIONAL REQUIREMENTS
Packaging and Storage: Preserve in cylinders.
