01Keep units explicit
One percent equals 10,000 parts per million on the same fraction basis. Converting the units is straightforward, but interpreting a purity claim requires more care. State whether the reported figure is an oxygen volume fraction and whether the gas is assessed on a dry or wet basis.
02Do not subtract away other components
Subtracting residual oxygen from 100% does not by itself establish the N₂ volume fraction because argon and other constituents may remain. Some commercial nitrogen specifications use an oxygen-based convention; that convention should be stated clearly rather than presented as a full composition measurement.
03Write the requirement directly
If the process controls residual oxygen, specify that limit and its test method. Add separate moisture or contaminant requirements where relevant. This is clearer for acceptance than relying on a rounded nitrogen-purity label whose calculation basis is unknown.
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- Official reference: servomex.com ↗
- Official reference: servomex.com ↗
- Official reference: parker.com ↗