with frontal analysis (FA), the d e -dadsorpb i s o t h m d insulin on the composition of mobile phase in reversed phase liquidchromatography(RPLC) has been inwdgated. ' Ibi9 is elso a good example to empIoy the stoirhiometric dkpkmed theory (SDT) for i n * dute adsorpbion in physical &*j . six ldnasofmobllephrse in RPLC Wem anployed to study the eat& 011 the elution curves and adsorption isdherns of insulin. llle key ~o f t h k p a p e r a r e : ( 1 ) ' I b e s t a b i l l t y o f~d u e t o d e l a y time after p-, the organic sdveut cwcentrstian, the kind and the concentration of ion-peiring agent in mobile phase wen found toaffectbotb elutioo QVM and adsorptionisdherm vergser i d y . (2) To obtain a valid and ComparaMe result. the Campositloo dthe mobile paaSe employed in FA must be as same as to that in usual RPLC of either analytical d e or prepdive purtate these obtained adforption isotherm. 'Ibe q r e s i o n for sdute adsorption from sdution ofthe SDT wa3 found to have a better elu-cidafkmtotheimulinadsorpti~frommobUe~inRpu3r. pose. (3) Lengmuir Equation and the SDT m employed to hni-Keywords phase liguid C -(RPLC), did-liquid system, stoichiometric displacement theory (SDT) , adsarption mechanism, adsorption isotherm, fmntal adysie (FA), insulin *