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Frequently Asked Questions

Gas Composition

Jun 22, 2020, 15:43 PM
Title : Gas Composition

Environmental Grades

  • NTRM - NIST Traceable Reference Materials are certified by the National Institute of Standards and Technology (NIST) and accepted by the Environmental Protection Agency (EPA), as the highest accuracy standards commercially available. These standards are the regulatory equivalent to NIST’s Standard Reference Materials (SRMs) and are made up of the same components and are within the analytical range of NIST SRMs.
  • EPA Protocols - Used for the calibration and audit of Continuous Emission Moni - tors (CEMs), Praxair EPA Protocols are NIST traceable and produced in accordance with the latest EPA specifications found in document-600/R97/121 Rev. 9/97.
  • Primary Master - High accuracy mixtures prepared gravimetrically on electronic high-precision balances. These standards are analyzed and named against NIST traceable reference materials.
  • Certified Master - These routine calibration mixtures are prepared by either gravimetric, volumetric or partial pressure methods and analyzed against NIST traceable reference materials.
  • Dynamic-Blend Master - These zero blend tolerance mixtures are prepared on an instrument based dynamic blending system. Batches of cylinders from two to one hundred can be produced with the identical concentrations.
  • Dynamic-Blend Standard - These mixtures are prepared similarly to the Dynamic Blend Master. Certification of the mixtures is based on process accuracy and Praxair Primary Laboratory Standards (PPLS).

All master gases are analyzed and named against NIST traceable materials.

EV - Environmental Grades1

Mixture Grade Order Reference Mixture Component Concentration Range Blend Tolerance Analytical Uncertainty
NTRM T N/A N/A ± 1%
EPA Protocol E 2 ppm - 25 ppm
25.1 - 49.9%
± 10%
± 5%
± 1%
± 1%
Primary Master PM 1 ppm - 9.9 ppm
10 ppm - 25 ppm
25.1 ppm - 9999 ppm
1.0% - 49.9%
± 10%
± 10%
± 5%
± 2%
± 0.1 ppm
± 1%
± 1%
± 1%
Certified Master CM 1 ppm - 9.9 ppm
10 ppm - 25 ppm
25.1 ppm - 9999 ppm
1.0% - 49.9%
± 20%
± 20%
± 10%
± 5%
± 0.2 ppm
± 2%
± 2%
± 2%
Dynamic Blend Master DM 1 ppm - 99.9 ppm
100 ppm - 49.9%
Zero
Zero
± 2%
± 1%
Dynamic Blend Standard D 1 ppm - 99.9 ppm
100 ppm - 49.9%
Zero
Zero
± 5%
± 2%

* Whichever is smaller.

1 All Environmental Grades are NIST traceable. Actual ranges, blend tolerance and analytical uncertainty are based on available National Institute of Standards and Technology (NIST) SRM concentrations. Please see individual components for specific information.

Standard Grades

  • Primary Standard - Highly accurate mixtures prepared gravimetrically on high-precision electronic balances. These standards are analyzed against Praxair Primary Laboratory Standards (PPLS) and named to a gravimetrically generated concentration.
  • Certified Standard - These routine calibration mixtures are prepared by either gravimetric, volumetric or partial pressure methods. These standards are analyzed against Praxair Primary Laboratory Standards (PPLS).
  • Non-Certified - Mixtures are prepared by the same methods and the same care used for Certified Standard Grades. Analyses are not reported.
  • Custom - Mixtures prepared to the exact blend tolerance and analytical uncertainty requested

ST - Standard Grades

Mixture Grade Order Reference Mixture Component Concentration Range Blend Tolerance Analytical Uncertainty
Primary Standard p 1 ppm - 9.9 ppm
10 ppm - 25 ppm
25.1 ppm - 9999 ppm
1.0% - 49.9%
± 10%
± 10%
± 5%
± 2%
± 0.1 ppm
± 1%
± 1%
± 1% or 0.02% abs*
Certified Standard C 1 ppm - 99.9 ppm
100 ppm - 999 ppm
0.1% - 49.9%
± 20%
± 10%
± 5%
± 5%
± 2%
± 2%
Non-Certified Standard U 1 ppm - 999 ppm
0.1% - 49.9%
± 20%
± 10%
N/A
Custom Standard Z 1 ppm - 49.9% TBD TBD

Note: For all mixtures, blend tolerance and analytical uncertainty specification may vary depending on the chemical characteristics of the component and the cylinder size. For mixtures outside of these ranges, please contact your local Praxair representative.

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