Depending on the requirements, the inside surface of the cylinder is treated by various methods. Irrespective of this, specialty gas cylinders are subjected to a comprehensive purge/evacuation cycle with the cylinders being heated during this procedure. This ensures removal of even traces of previously filled gases, vapors and especially moisture to a level that is below the limit of detection.
In special cases (e.g. mixtures with low corrosive components) the result of the purge process is checked by a moisture measurement. Only through such thorough and systematic cylinder pretreatment it is possible to prepare stable calibration gas mixtures.