Effect of column combinations on two-dimensional separation in comprehensive two-dimensional gas chromatography: estimation of orthogonality and exploring of mechanism.

With the analysis of Chinese liquor Moutai as an example, the effect of different column combinations was studied on two-dimensional separation in comprehensive two-dimensional gas chromatography (GCxGC). A method to optimize column combinations was developed for achieving maximum orthogonality. Using a geometric approach to factor analysis, the degree of separation orthogonality was quantitatively estimated. The parameters evaluated include peak spreading angle, retention correlation, and practical peak capacity. When using the "reversed-type" column combinations (a polar column as the first dimension and a non- or less polar one as the second dimension), correlation coefficient was lower than or equal to 0.221, the spreading angle was higher than or equal to 77 degrees , and more than 92% of the theoretical peak capacity was reasonably used. For Moutai liquor mainly consisting of some polar compounds, the HP-Innowax+DB1701 column combination was optimal. In addition, through the test of Grob mixture and McReynolds constant, the mechanism of solute-stationary phase interactions was disclosed in details, which validated the estimation of GCxGC orthogonality in a molecular level.