The behaviour towards simultaneous oxidation by Cr(VI) in acidic environment of mixtures consisting of two structurally closely related thioethers (S-methylcysteine and DL-methionine) was tested, at 0.085 mol·l -1 H + and 298  0.1 K. The kinetic and mechanistic patterns of the two substrates when oxidized separately were already known and very similar. Based on that knowledge, the individual kinetic parameters (rate and equilibrium constants) were first computed. Theoretical predictive models

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... or the value of the observed rate constant of a mixture, based on the kinetic data from non-mixtures, are compared with experimental findings and subsequently an empirical calibration surface obtained from all experiments is discussed. Due to differences in the kinetic parameters of the two reactions, in all models the obtained surfaces are asymmetrical, and this opens the possibility to univocally determine the concentrations of both the thioethers without separation.