Patent ID: 7107818

Claim:
A method for detecting substances or mixtures of substances within a sample in an apparatus for comprehensive two-dimensional gas-chromatographic analysis, comprising the steps of: subjecting the sample to a first separation within a first capillary column; modulating in time the effluents from the first column by subdividing said effluents from the first column into adjacent fractions and by then sending each fraction into a second capillary column, said modulation of the effluents being periodic, with a first modulation frequency of the sample f 1 ; separating each of the fractions in said second capillary column; detecting, at the end of said second capillary column, the effluents by means of periodic sampling by discrete time points at a second frequency f 2 ; and generating said first frequency f 1 of modulation and said second frequency f 2 of sampling in such a way that said first frequency f 1 coincides with, or is a multiple or submultiple of, said second frequency f 2 and said sampling by discrete points will be in phase with said modulation of the effluents from said first column.