Direct surface analysis by infrared spectroscopy is a useful technique for detection of xanthate species on sulphide minerals, However, infrared detection limits require xanthate dosages that are often one or two orders of magnitude higher than are used in practice. This paper presents an alternative approach to the analysis of collectors on mineral surfaces. A novel gas-phase infrared technique (HAGIS) has been applied to the indirect analysis of ethylxanthate on lead, zinc and copper sulphide mineral surfaces and also on flotation products from copper-zinc and lead-zinc ores at xanthate concentrations which are comparable to those used in the mineral processing industry. HAGIS relies on the detection of the gas-phase species generated by the thermal decomposition of xanthates adsorbed on mineral surfaces. In this study, the primary decomposition products generated under an air atmosphere include carbonyl sulphide (COS), carbon dioxide (CO2), carbon disulphide (CS2) and ethanol. The amounts of these species were compared with product distributions observed for the decomposition of known ethylxanthate complexes. Correlations between the decomposition species provide evidence for the speciation of the collector in the flotation product. The decomposition species can be readily detected from xanthate dosages that are much lower than are the detection limits of traditional, direct surface analysis techniques.