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

Abstract

Partial modulation via a pulse flow valve operated in the negative pulse mode is developed for highspeed one-dimensional gas chromatography (1D-GC), comprehensive two-dimensional (2D) gas chromatography (GC × GC), and comprehensive three-dimensional gas chromatography (GC 3 ). The pulse flow valve readily provides very short modulation periods, P M , 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 s ≥ 1.5) in a 200 ms window, providing a peak capacity, n c , of 14 at unit resolution (R s = 1.0). Additionally, the pulse width, p w , of the pulse flow valve "injection" relationship to peak width-at-base, w b , 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, 2 D, with 2 w b ranging from 7 to 12 ms, providing an exceptional 2 D peak capacity, 2 n c , of ∼12 using a modulation period (P M ) of 100 ms. Next, a 12 min separation of a diesel sample using a P M of 300 ms is presented. The 1 w b is ∼4 s, resulting in a 1 n c of ∼180, and 2 w b is ∼18 ms, resulting in a 2 n c of ∼17, thus achieving a n c,2D of ∼3000 in this rapid GC × GC diesel separation. Finally, GC 3 with time-of-flight mass spectrometry (TOFMS) detection using a P M of 100 ms applied between the 2 D and 3 D columns is reported. Narrow third dimension, 3 D, peaks with 3 w b of ∼15 ms were obtained, resulting in a GC 3 peak capacity, n c,3D , of ∼35 000 in a 45 min separation.

Latest Trends on the Future of Three-Dimensional Separations in Chromatography

“…The authors focused on the relative phase ratios of the columns in the different separation dimensions to maximize the peak capacity. Using partial modulation using a pulse flow valve operated in a negative pulse mode to create extremely narrow, local analyte concentration pulses, the same group obtained 3 D peaks with a peak width-at-base of 15 ms resulted in a GC × GC × GC peak capacity of about 35 000 in a 45 min separation . The gain in peak capacities, thus, demonstrated during the past few years is extremely promising.…”

“…Using partial modulation using a pulse flow valve operated in a negative pulse mode to create extremely narrow, local analyte concentration pulses, the same group obtained 3 D peaks with a peak width-at-base of 15 ms resulted in a GC × GC × GC peak capacity of about 35 000 in a 45 min separation. 16 The gain in peak capacities, thus, demonstrated during the past few years is extremely promising. Further gains in peak capacities can be expected as ongoing developments in GC × GC × GC instrumentation are made.…”

“…If a mixture features clear and dominant sample dimensions, as is the case in mineral oils, structured chromatograms can be obtained that facilitate qualitative analysis. A third GC dimension may be added to create comprehensive three-dimensional gas chromatography, − but the chemical selectivity may be enhanced further by adding different dimensions. For example, the online coupling of LC, − or supercritical fluid chromatography (SFC) − to GC × GC may enhance so-called “group-type” separations of different classes of compounds.…”

Comprehensive Two-Dimensional Gas Chromatography Hyphenated with a Vacuum Ultraviolet Spectrometer To Analyze Diesel—A Three-Dimensional Separation (GC × GC × VUV) Approach

“…1 However, component coelution still remains problematic in the chromatographic separation of natural crude oils and refined hydrocarbon products. Resolving coelution after multidimensional gas chromatographic separation is a challenging task and necessitates the development of additional multidimensional techniques, such as comprehensive threedimensional gas chromatography (GC × GC × GC) 2 and comprehensive two-dimensional gas chromatography hyphenated with field ionization mass spectrometry (GC × GC × FIMS). 3 The concept of separation via a multidimensional approach does not have to be limited to chromatographic techniques.…”

Quasi-Stop-Flow Modulation Strategy for Comprehensive Two-Dimensional Gas Chromatography

“…While advances in thermal modulation have been focused primarily on overcoming ease-of-use and cost of cryogenic fluid consumption, − advances in flow modulation have been driven by more diverse goals. These goals include reducing carrier gas flow rate for flow compatibility with contemporary mass spectrometers, − more freely increasing secondary dimension separation time using stop-flow techniques, , enhancing modulator performance or versatility with multiport microfluidic devices, − and high-speed analysis using fast-response valves, to name a few. − …”