NITROGEN
Prepared at the 53rd JECFA (1999) and published in FNP 52 Add 7 (1999),
superseding specifications prepared at the 51st JECFA (1998), published in
FNP 52 Add 6 (1998). ADI "No ADI necessary" established at the 24th
JECFA in 1980.
SYNONYMS INS No. 941
DEFINITION This monograph defines nitrogen with a maximum oxygen content of 1%,
which is suitable only for some food applications. There are food
applications that require a higher purity (i.e., lower oxygen content).
Chemical names Nitrogen
C.A.S. number 7727-37-9
Chemical formula N2
Formula weight 28.0
Assay Not less than 99.0% v/v
DESCRIPTION Colourless, odourless gas or liquid
FUNCTIONAL USES Freezing agent, propellant, packaging gas
CHARACTERISTICS
IDENTIFICATION
Flame test A flame is extinguished in an atmosphere of the sample
PURITY
Oxygen As declared by the vendor but not more than 1% v/v
See description under TESTS
Carbon monoxide Not more than 10 µl/l
See description under TESTS
TESTS
PURITY TESTS
Oxygen Use an oxygen analyser with a detector scale ranging from 0 µl/l to 100 µl/l
and equipped with an electrochemical cell. The gas to be examined is
passed through a detection cell containing an aqueous solution, generally
potassium hydroxide. Oxygen in the sample gas produces variation in the
electrical signal recorded at the outlet of the cell that is proportional to the
oxygen content.
Calibrate the analyzer according to the instructions of the manufacturer.
Pass the gas through the analyser using a suitable pressure regulator and
airtight metal tubes and operating at the prescribed flow-rates until constant
readings are obtained.
Carbon monoxide Pass 1050 ± 50 ml of the gas sample through a carbon monoxide detector
tube at the rate specified for the tube. The indicator change corresponds to
not more than 10 µl/l.
METHOD OF Determine by Gas chromatography using the following conditions:
ASSAY
Column:
- material: stainless steel
- length: 2 m
internal diameter: 2 mm
packing material: appropriate molecular sieve capable of absorbing
molecules with diameters up to 0.5 nm.
Carrier:
- gas: helium (not less than 99.995 % (v/v) of He)
- flow: 40 ml/min
Detector: thermal conductivity detector
Injector: loop injector
Column temperature: 50°
Detector temperature: 130°
Reference gas (a): ambient air
Reference gas (b): Nitrogen (not less than 99.999 % (v/v) of N2, less than 1
ppm CO, less than 5 ppm O2)
Procedure:
Inject reference gas (a). Adjust the injected volumes and operating
conditions so that the height of the peak due to nitrogen in the
chromatogram is at least 35 % of full scale of the recorder. The assay is not
valid unless the chromatograms obtained show a clear separation of oxygen
and nitrogen.
Inject the gas to be examined and the reference gas (b). In the
chromatogram obtained with the gas to be examined, the area of the
principal peak is at least 99.0 % of the area of the principal peak in the
chromatogram obtained with reference gas (b).
