Recertification is available for gas standards. Gas standards can be expensive and tend to be stored in the lab for months, if not years, so it is wise to have the composition recertified by a qualified vendor. For gas standards purchased from Restek, request recertification directly from Linde Gases (1-800-932-0624) or Airgas (1-800-331-4953). For gas standards purchased from vendors other than Restek, it is necessary to contact the vendor who manufactured the mixture.
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