Gray butyl rubber stoppers contain zinc in the form of zinc-oxide. Choosing a suitable stopper material is very essential for studies related to denitrification coupled to methane oxidation. In some cases stoppers are replaced with sterile PTFE mininertvalves or PTFE-faced grey butyl rubber stoppers, for containment of voltiles.
Gray butyl rubber stopper was used to seal the serum vials for isotopic analyses of CH4, during an experimental study done to determine the concentration and carbon isotopic composition of dissolved methane in porewaters. It may also be used to seal aluminium tubes containing growth media, used for assaying conditions for carbon monoxide oxidation by Clostridium thermoaceticum and Clostridium formicoaceticum.