Method to determine the true modulation ratio for comprehensive two-dimensional gas chromatography.

Abstract A new method is presented to determine the true modulation ratio, M R , from the measurable effective modulation ratio, M R *, in comprehensive two-dimensional gas chromatography, GC × GC, without the requirement for a detector at the end of the primary column. The method was developed through the investigation of modulator induced band broadening, as a function of 1 W b and the selected modulation period, P M , for simulated GC × GC data, by first defining primary column 1 D peak(s) and simulating the modulation process. Gaussian curve fitting is used to model each modulated secondary column separation peaklet, 2 D, in the unfolded GC × GC data to accurately determine the maxima of the peaklet distribution, followed by Gaussian curve fitting to the maxima to determine the effective 1 D peak profile and width, 1 W b *. The relationship between 1 W b and 1 W b * is studied as a function of the effective modulation ratio, M R *, which is 1 W b * divided by P M , in order to determine the true modulation ratio, M R , which is 1 W b divided by P M . We explore how peak sampling phase (in-phase and out-of-phase) plays a role in the relationship between M R and M R *. Experimental validation of the simulated results is also provided, to span a range of commonly implemented conditions with typical 1 W b (2–4.5 s) and P M (0.25–8 s). Use of M R 1 D peak ( M R * ≥ 1.2  M R ) corresponding to a loss in 1 D peak capacity, 1 n c  ≥ 20%. The new method relies upon mapping from M R * to M R , which is discussed in relation to peak capacity theories for GC × GC. It is found that optimizing 1 n c in GC × GC requires that 1 W b is minimized and must be sampled with a sufficiently short P M (1–2 s) to minimize modulator induced band broadening and a subsequent reduction in the effective 1 D peak capacity.