Abstract: The gas chromatographic retention indices can be used to qualify some organic compounds. A new topological index based on distance matrix and branch vertex of the atoms in a molecule is proposed by defining equilibrium electronegativity of atoms in the molecule and coloring atoms in the molecular graph with equilibrium electronegativity, which appears unique to the molecular structures and has excellent structural selectivity. The multivariate linear equations of gas chromatographic retention indices are as follows: I(Squalane)=23.97842N1-3.86562N2+0.787379N3+42.33061, R=0.9922, n=70, S=13.70405, F=1396.601; I(SE-30)=23.83937N1-3.5687N2+0.939876N3+22.11952, R=0.9919, n=37, S=11.96088, F=668.8781; where the N1, N2 and N3 are a group of topological indices; n, R, S and F are sample number, regression coefficient, residual standard deviation and F-statistic value, respectively. The calculated results by the formulae indicate that the average relative deviations between calculated values and experimental data of gas chromatographic retention indices of alkane series on both squalane(column temperature 50 ℃) and SE-30 (column temperature 80 ℃) were all 1.31% and the errors were within experimental deviations. The equations can express well the change rule of the relative gas chromatographic retention indices of alkane series.

Key words: atom, quantitative structure-retention relationship , equilibrium electronegativity, gas chromatographic retention index, topological index, alkane