ENAC has recently granted Carburos Metálicos the first accreditation as a reference material producer of gas mixtures, in accordance with the requirements established in the UNE-EN ISO 17034 standard. Thereby, Carburos Metálicos can produce nitrogen-based gas mixtures with certified propane, carbon monoxide, carbon dioxide and/or oxygen contents, in the ranges and uncertainties indicated in its Technical Annex.

Carburos Metálicos therefore becomes a producer of certified reference materials, CRM, in accordance with the ISO 6142-1:2015 standard, Gas analysis. Preparation of Gas Mixtures for Calibration Part 1: Gravimetric Method for Class I Mixtures, which, as its title suggests, uses the gravimetric reference method for characterizing the reference values of the components of the mixtures.

 

Distinctive value of the new accreditation compared to accredited calibration

Traditionally, before accreditation bodies had an accreditation scheme for reference materials producers, the way to ensure CRM traceability was based on being accredited as a calibration laboratory for the laboratory that determined the value of the certified property. So, both accreditations currently coexist.

Although the two accreditations qualify to provide traceability to the certified property, only the accreditation as a reference materials producer in accordance with ISO 17034 covers the production phases of the materials, their stability and homogeneity assessment and even the distribution service, ensuring the quality and reliability of all of them.

In summary, accreditations according to ISO/IEC 17025 (calibration laboratories) and ISO 17034 (reference material producers) differ in the following key points:

• Scope: Accreditation according to ISO 17034, unlike accreditation in calibration, covers all CRM production phases. The aim of these manufacturing steps is to achieve reference materials with the intended value of certified ownership and, moreover, to achieve the fundamental characteristics of a reference material, i.e. homogeneous and stable.
• Stability assurance: Accreditation according to ISO 17034 establishes requirements for assessing homogeneity and stability including monitoring during the validity period, allowing it to be used as a reliable reference over time. Calibration laboratories, on the other hand, only certify the condition of the calibrated object at the time of calibration, without offering guarantees on its future stability.
• Additional information: MRC certificates under ISO 17034 standard may include relevant information on their use, for example, the minimum sample size required or storage and handling conditions, aspects that are not included in calibration certificates.

In addition, in the specific case of gas mixtures, although both accreditations have a shared objective, that of providing metrological traceability to the gases used by users for calibrating their equipment, accreditation as a producer of reference material provides a distinctive value. Therefore, the ISO 17034 standard sets out requirements for producing the reference materials applicable in this case, in which the body carries out the reference material manufacturing process from the raw materials. By using gravimetry as a method of adding components to the bottle, the producer can minimize the uncertainties with respect to those that would be obtained by the chromatographic analysis that would be applied in calibration.