Modeling the nonlinear behavior of a bioactive peptide in reversed-phase gradient elution chromatography.The thermodynamic behavior of octreotide, a cyclic octapeptide with important pharmaceutical functions, has been simulated under reversed-phase gradient elution conditions.  To this end, adsorption behavior was firstly investigated in isocratic conditions, under a variety of water/acetonitrile + 0.02% (v/v) trifluoroacetic acid (TFA) mixtures as mobile phase by using a Langmuir isotherm.  Adsorption isotherms were determined by means of the so-called Inverse Method (IM) with a minimum amount of peptide.  The linear solvent strength (LSS) model was used to find the correlation between isotherm parameters and mobile phase composition. 
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