Pulsed Flow Modulation for High-Speed GC Using a Pressure-Tunable Column Ensemble

Abstract

A computer-driven pressure controller is used to deliver pressure pulses to the junction point of two series-coupled columns using different stationary-phase chemistries. The column ensemble consists of a trifluoropropylmethyl polysiloxane column followed by a dimethyl polysiloxane column. Each pressure pulse causes a differential change in the carrier gas velocities in the two columns, which lasts for the duration of the pulse. A pressure pulse is used to selectively increase the separation of a component pair that is separated by the first column but coelutes from the series-coupled ensemble. If both components are on the same column when the pulse is applied, a small change in the ensemble separation occurs. If one component of the pair is on the first column and the other component is on the second column, a pressure pulse can result in a much larger change in the ensemble separation for the component pair. A model with a spreadsheet algorithm is used to predict the effects of a pressure pulse on the trajectories of component bands on the column ensemble. The effect of the initiation time of a pressure pulse is investigated for a two-component mixture that coelutes from the column ensemble. For the case where the entire pressure pulse occurs when one of the components is on the first column and the other component is on the second column, the peak separation from the ensemble increases nearly linearly with the product of the pressure pulse amplitude and the pulse duration. Peak shape artifacts are observed if the pressure pulse occurs when a solute band is migrating across the column junction point.

Ultra‐fast essential oil characterization by capillary GC on a 50 μm ID column

“…The fast GC-TOFMS (time-of-flight MS) analysis of a grapefruit essential oil, using a 14 m6180 lm capillary column ensemble, which was temperature programmed at 50 K/min, was reported recently [4]. The analysis of the volatile essential oil fraction was completed within 200 s; however, the chromatogram contained severely overlapping peaks, and the authors relied on pressure tuning and mass-spectral deconvolution to identify and quantify individual components.…”

Rapid analysis of food products by means of high speed gas chromatography

“…The latter reports essential information relative to each application, which will not be repeated in this section (more details may be derived by directly consulting the reference). In the field of narrow-bore column fast GC research, a total of 18 essential oil applications are reported [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]; Table 1 also reports the use of a short conventional column in fast GC essential oil analysis [9], while eight are focussed on fatty acid methyl ester (FAME) analysis [44][45][46][47][48][49][50][51]; single works regard triglycerides [52] and an alcoholic beverage [53]. More detailed information will be provided hereafter for some of the most representative high-speed GC examples.…”

High-speed analysis of residual solvents by flow-modulation gas chromatography

“…The pneumatic valve is operated by a 50-55 psig compressed air source (1 psi = 6894.76 pa), connected through an electronically-actuated solenoid valve (Model GH3412, Precision Dynamics, Phoenix, AZ, USA). The configuration of the system is described in greater detail in [6]. Ballast chamber pressure is controlled by an electronic pressure controller (MKS Model 640 A, MKS Instruments, Andover, MA).…”

“…A flow-modulation technique has been described in detail by Sacks et al [3][4][5][6], and has been applied to complex mixtures such as chlorinated pesticides and essential oils [7][8][9]. This technique is performed by programming the carrier gas pressure at the junction point of a series-coupled (tandem) ensemble of capillary columns that exhibit differing selectivity for the target compounds to be analyzed.…”

“…Components that are separated by the first column in the ensemble, but then co-elute from the second column, can be separated by the column pair if the valve is opened briefly when the band for one of the components has crossed the column junction point but the band for the other component is still in the first column. Pressure pulses at the junction of the column ensemble have been shown to be useful for increasing the separation between components without adversely affecting the separation of other components in the mixture [6][7][8][9]. Using series-coupled capillary columns with pressure switching techniques and fast oven temperature programming, it is possible to achieve resolution of 36 commonly analyzed organic volatile compounds in an analysis time of 12 min.…”