Long-term test to determine the stability of gas mixtures: methodology to ensure the system consistency and stability for gas mixture preparation.

Laura Gagni, Società Italiana Acetilene e Derivati – SIAD’ [i.e. “- SIAD”] (IT)

It is presented the results of a long-term stability study, 15 years, using the following binary gases mixtures: sulfur dioxide 150 ppm; benzene 15 ppb; nitrogen dioxide 50 ppm; hydrogen 2%; nitric oxide 1 and 10 ppm; carbon monoxide 2 ppm; oxygen 1200 ppm and 5%; propane 10 ppm; nitrous oxide 2 ppm; carbon dioxide 350 ppm.
For each mixture, a batch of five cylinders of the same concentration were prepared. The mixtures were analyzed periodically, both by comparing their concentration and versus other mixtures that, in the meantime, have been produced.
The study allows achieving the following results:
– provide information on mixtures stability over a long period;
– evaluate the fluctuations of the production system over a long period.
In the gas mixtures production systems, its consistency over time is ensured by:
– internal procedures;
– external audits;
– comparison with metrological gas mixture.
External audits check the quality system while the comparison certifies the compatibility of the mixtures evaluated.
The methodology proposed will add long-term internal studies to keep under control the whole production cycle in a more comprehensive manner; this methodology will also lead to know the system fluctuations parameter. This latter figure emerges from the periodic comparison of the “historic” batch when compared with the mixtures produced over time. In this comparison are, in fact, involved both the “historic” batch, the new mixtures and the analysis system during the time. Even if the results of the “new” gas mixtures are compatible with international standards, it is to assess whether in the uncertainty budget of the mixture, should also be included the additional contribution due to the long period oscillation of the system.

Pen Profile

Laura Gagni was born in Bergamo, Italia. She studied at the Politecnico di Milano and obtained Master’s Degree in Chemical Engineer in 2011. Since 2012 she has been employed in the research and Specialty Gas Department of SIAD in Osio Sopra, Bergamo. Since 2013, she is Quality and Metrology Responsible of the SIAD accredited Centre N°143 and Certified Reference Material Producer RMP N°143.

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