X-ray photoelectron spectroscopy and time of flight secondary ion mass spectrometry have been used to determine the specific effect of sulphite ions on the surface chemistry of copper-activated pyrite pre-treated with isobutyl xanthate in flotation experiments with nitrogen and air purging at pH 7. The results from these spectroscopic techniques illustrate that sulphite ions affect the surface chemistry of pyrite similarly whether nitrogen or air purged. It was found that sulphite ions interact with adsorbed collector species, as well as with the pyrite surface itself. A reduction in the adsorbed collector concentration and a commensurate increase in surface hydrophilicity explain the low flotation recovery of pyrite in the presence of sulphite. As expected, this effect was more pronounced in the flotation experiments with air purging. (C) 2003 Elsevier Science Ltd. All rights reserved.