A systematic investigation of comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry with dynamic pressure gradient modulation for high peak capacity separations

Dynamic pressure gradient modulation (DPGM) in full modulation mode is optimized for comprehensive two-dimensional (2D) gas chromatography (GC x 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 (D-1) column to the second dimension (D-2) column. At a sufficiently high auxiliary pressure (P-aux) the D-1 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 D-1 effluent to essentially be reinjected onto the D-2 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 F-1 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 D-1 peak capacity of (1)n(c) = 330 and a 2D peak capacity of (2)n(c) = 15, hence an ideal 2D peak capacity n(c,2D) = x (2)n(c) = 4950. Likewise, the 2D peak capacity corrected for undersampling of the D-1 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 x 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. (C) 2020 Elsevier B.V. All rights reserved.