Transfer of CO2, N2O and CH4 to butyl rubber (polyisobutylene) septa during storage

Abstract

Greenhouse gases are more sampled than ever because of environmental interests. Gas samples are often inserted into vials with gas tight butyl rubber septa before concentration analysis. Little is known on the global transfer property of butyl rubber septa for CO₂, N₂O and CH₄. Sorption kinetics were measured by injecting CO₂, N₂O or CH₄ into glass vials with either one of four butyl rubber septa types and stored during 90 days. CO₂ and N₂O concentrations decreased during storage depending upon septa type and initial concentration, with the highest linear rate being 0.023 for CO₂ and 0.0015 mg L⁻³ day⁻¹ for N₂O. When a low concentration was injected, CH₄ concentration changes over time were small and did not differ between septa types. Sorption isotherms were measured using nine concentrations and stored during 45 days. CO₂ sorption isotherms ranged from 0 to 3.7 × 10⁻³ m³m⁻² and N₂O from 0.3 to 1.4 × 10⁻³ m³m⁻². Examples of errors associated with the use of these butyl rubber septa are given.