Development of Ultrafast Separations Using Negative Pulse Partial Modulation To Enable New Directions in Gas Chromatography.

Partial modulation via a pulse flow valve operated in the negative pulse mode is developed for high-speed one-dimensional gas chromatography (1D-GC), comprehensive two-dimensional (2D) gas chromatography (GC × GC), and comprehensive three-dimensional gas chromatography (GC). The pulse flow valve readily provides very short modulation periods, P, demonstrated herein at 100, 200, and 300 ms, and holds significant promise to increase the scope and applicability of GC instrumentation. The negative pulse mode creates an extremely narrow, local analyte concentration pulse. The reproducibility of the negative pulse mode is validated in a 1D-GC mode, where a pseudosteady-state analyte stream is modulated, and 8 analytes are baseline resolved (resolution, R ≥ 1.5) in a 200 ms window, providing a peak capacity, n, of 14 at unit resolution ( R = 1.0). Additionally, the pulse width, p, of the pulse flow valve "injection" relationship to peak width-at-base, w, resolution between peaks and detection sensitivity are studied. To demonstrate the applicability to GC × GC, a high-speed separation of a 20-component test mixture of similar, volatile analytes is shown. Analytes were separated on the second-dimension column, D, with w ranging from 7 to 12 ms, providing an exceptional D peak capacity, n, of ∼12 using a modulation period ( P) of 100 ms. Next, a 12 min separation of a diesel sample using a P of 300 ms is presented. The w is ∼4 s, resulting in a n of ∼180, and w is ∼18 ms, resulting in a n of ∼17, thus achieving a n of ∼3000 in this rapid GC × GC diesel separation. Finally, GC with time-of-flight mass spectrometry (TOFMS) detection using a P of 100 ms applied between the D and D columns is reported. Narrow third dimension, D, peaks with w of ∼15 ms were obtained, resulting in a GC peak capacity, n, of ∼35 000 in a 45 min separation.