Abstract: The retention values of eight organic solutes(i)(benzene,tetrachloromethane,chloroform,dichloromethane,ethyl acetate,tetrahydrofuran,acetone and methyl ethyl ketone)in stationary solution of urea(j)+sodium perchlorate (k)+formamide (s) at 298.15 Khave been measured by a gas-liquid chromatographic method(GLC).The McMillan-Mayer's solution theory,in which all the thermodynamic excess properties of multi-component solution can be expressed by a virial expansion,was used to relate the excess Gibbs free energy of the system to a series of pairs,triplet and higher order interaction parameters. An equation for expressing the relationship between the interaction parameters and the specific retention volume(V_g)of GLCwas obtained,that RTln [V_g(s+j)/V_g(s+j+k)]=2vg_ikm_k+3v²g_ikkm_k+6vg_ijkm_jm_kwhere V_g(s+j)and V_g(s+j+k)are the specific retention volumes of organic solutes (i) in multi-component stationary solution of s+j and s+j+k respectively.gik is the pair interaction parameters between i and k, g_ikkand g_ijkare the triplet interaction parameters of i-k-k and i-j-k.The values of g_k,g_ijkikkj,m_kand V_gdata to the equation given above. Some information about the solute(i)-solute(k) interaction in formamide and the effect of urea on g_ik have been discussed,For all solutes of i,g_ik>0,that means the interaction of i and k makes a positive contribution to G_i^EIn the presence of urea,the g_ikvalues become more positive than those in the absence of urea,which enhance the salting-out effect on the noneiectrolyte solutes.For the values of triplet interaction parameters,g_ijk<0,and the contribution of g_ikkto G_i^Ecan be neglected.

Key words: Gibbs free energy interaction parameter, Gas liquid chromatography, Organic solute, Quaternary mixture