Primary Standard: Primary standards are high accuracy mixtures blended gravimetrically on electronic, high load precision balances. The balances are calibrated against NIST Traceable weights. After blending, post run calculations are performed to estimate the expected concentration of the candidate standard. The candidate standard is then confirmed by instrument analysis against NIST Traceable standards. The result of the analysis is compared to the expected concentration from the post run calculations and if the two results are statistically equal, the post run calculated value is used to name the mix as a primary standard. Upon request, a primary standard can certified as NIST Traceable and a certificate of analysis will be prepared indicating that the balance was calibrated in accordance with ISO 6142 and that the analysis was conducted as a direct comparison between the candidate gas mixture and a NIST SRM or its recognized equivalent. The use of SRM materials provides an unbroken chain of measurements directly against a NIST gas standard. This unbroken chain of measurements is the only acceptable method of establishing traceability of a gas analysis to the National Institute of Standards and Technology.
Certified Standard: Certified gas mixtures are prepared by either gravimetric, volumetric or partial pressure methods. Component concentration is established with instrument analysis using Global Calibration Gases primary lab standards as reference materials.