A systematic investigation of comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry with...

Dynamic pressure gradient modulation (DPGM) in full modulation mode is optimized for comprehensive two-dimensional (2D) gas chromatography (GC × GC) with time-of-fight mass spectrometry (TOFMS) detection to obtain high peak capacity separations and demonstrate broad applicability for complex samples. A pulse valve introduces an auxiliary carrier gas flow at a T-union connecting the first dimension (¹D) column to the second dimension (²D) column. At a sufficiently high auxiliary pressure (P_aux) the ¹D flow is temporarily stopped. Then, during each modulation period (P_M) the valve is turned off briefly, a period termed the pulse width (p_w), allowing the ¹D effluent to essentially be reinjected onto the ²D column for the modulated separations. Modifications to the modulator assembly are provided to improve performance. Method optimization is demonstrated for a 116-component test mixture by tuning the P_aux and the p_w. For a P_M = 2 s and ¹F of 0.10 ml/min, the optimal p_w and initial P_aux selected were 200 ms and 330.9 kPa (33 psig), respectively. The 30 min separation of the test mixture provided a ¹D peak capacity of ¹n_c = 330 and a ²D peak capacity of ²n_c = 15, hence an ideal 2D peak capacity n_c,2D = ¹n_c × ²n_c = 4950. Likewise, the 2D peak capacity corrected for undersampling of the ¹D separation was 4500 and corrected for both undersampling and sampling variation via statistical overlap theory was 4090. These results provide a 2-fold improvement in peak capacity relative to the previous DPGM study in full modulation mode for GC × GC-TOFMS. The optimized conditions were applied for a variety of applications: diesel fuel, derivatized cow serum, solid phase microextraction (SPME) of coffee headspace, and SPME of river water headspace. Additionally, the fraction of 2D separation space utilized (f_coverage), as defined by the minimum convex hull method, ranged from 0.60 to 0.85. We observed that any f_coverage correction to 2D peak capacity is highly sample dependent, since all samples, except for the diesel sample, were run with the same separation conditions, and yet the f_coverage ranged from 0.60 to 0.80.