The beneficial effects of the synergy between two or more reagents were realized long time ago. The purpose of using a mixture of collectors was to increase both the recovery and selectivity. In this work, two thiol collectors, isopropyl xanthate (SIPX) and di-isobutyl dithiophosphinate (DTPI), having different chemical and functional properties, were used. The adsorption behaviour of these collectors from their mixtures was investigated at various SIPX:DTPI ratios and sequence of addition by cyclic voltammetry and adsorption experiments at pH 9.2. The results showed that both the ratio of collectors in these mixtures, and sequence of addition were important. The amount of total collector (SIPX and DTPI) adsorbed on chalcopyrite was measured for these various reagent mixtures and for single collectors. Two maxima were found. One was found for the 30:70 DTPI:SIPX suite in which the DTPI was added first. A second was found with the 50:50 SIPX:DTPI suite when the collectors were added together. These results revealed that the maximum synergistic effect of using mixture of SIPX and DTPI was strongly influenced by the ratio of the collectors in the mixture and particularly sequence of addition. (C) 2007 Elsevier Ltd. All rights reserved.