Cylinder preparation varies based upon product specifications.
Most common methods used to ensure gas mixture homogeneity include:
By partial pressure blending.
Full range of analytical instrumentation for certifying purity and mixture composition.
Since most analytical methods are relative and not absolute, it is necessary to calibrate the analyzer with reference calibration mixture standards of known composition and concentration to determine the quantitative content of the sample accurately. The requirements for a calibration gas are: accuracy stability and homogeniety. Several classes of mixtures are provided based on their certification and accuracy levels.
Blend tolerance specifies how close to the ordered concentration the produced mixture will be. The analytical uncertainty identifies the maximum deviation from the certified value that the actual blend mix can have.
Example: 5% minor component mixture. The reported value on the analytical certificate is 5.10% (within the 5% relative blend tolerance) with a certified accuracy between 5.00% and 5.20%.
Available in some regional offerings, the ISO 17025 international levels of certification are part of a detailed specific audit program to ensure a consistent quality audited by an external agency traceable to chemical reference standards of a metrological level.
Guide 34 sets out the management system requirements for the product reference materials and is intended to be used as part of a reference material producer’s general quality assurance (QA) procedures.