Nitrogen and ammonia plasma containment tubes of quartz and fused alumina (Al2O3) are evaluated in terms of the oxygen contamination contributed during gallium nitride film growth by RPE-CVD. In-situ gas and plasma monitoring, and material characterisation (UV-Vis transmission measurements, X-ray diffraction and SIMS) were used to determine the contaminant chemistries for the plasmas maintained in these containment tubes. Oxygen contamination using a quartz tube is shown to be unavoidable. Al 2O3 based tubes used with an ammonia plasma also supply unacceptably high levels of oxygen for GaN growth. However, we show that alumina containment tubes may be conditioned in a nitrogen plasma, so that an aluminium nitride protective layer limits the oxygen contamination.