Accumulating resampling (modulation) in comprehensive two-dimensional capillary GC (GC x GC).

During each sampling period, an accumulating resampler (modulator) in comprehensive 2-D chromatography accumulates all eluite from the first-dimension column and reinjects the whole or a portion of the accumulated material into the second-dimension column. The detrimental effect of the resampling on peak capacity of a 2-D separation comes from the broadening of the peaks along the first-dimension due to the resampling itself and due to the subsequent peak reconstruction. Sampling density (rho(S)) of resampling is the number of sampling periods per standard deviation of a peak at the outlet of the first-dimension column. It is shown that a simple formula describes the peak broadening as a function of rho(S) at any (even practically too low or too high) rho(S), for the peaks of any (not necessarily Gaussian) shape, for a wide class of peak reconstruction techniques, and for any 2-D separation (GC x GC, LC x LC, etc.). In capillary GC x GC, optimal rho(S) (rho(S,Opt)) depends on the type of the peak reconstruction and on the degree of the gas decompression along the second-dimension column. When reconstructing using linear interpolation, rho(S,Opt) = 0.7 at large and rho(S,Opt) = 0.5 at small gas decompression. The choice of exact optimal conditions is not critical. Thus, two-fold departure of actual rho(S) from rho(S,Opt) in either direction (under- or oversampling) causes only 10% drop in the net peak capacity of GC x GC. The quantitative effect of a much greater undersampling is also evaluated.