Development of Ultra-Fast Modulation for Application in Multi-Dimensional Gas Chromatography
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A combination of four instrumental systems and one chemometric method are presented that improves the efficiency, resolving power (i.e. peak capacity/ peak capacity production), and lessens the typical time of multi-dimensional gas chromatography (MDGC) separation in a straightforward, easily interpretable manner. Application of partial modulation via a commercially available high speed pulse flow valve for two-dimensional gas chromatography (GC×GC) is shown to provide ultra-fast modulation with modulation periods (PM) as short as 50 ms. This technique performs a combination of vacancy chromatography and frontal analysis by an injection of carrier gas at the union of the first column (1D) and second column (2D). Each pulse disturbance in the analyte concentration profile as it exits the first column (1D) results in vacancy like data that is readily converted into a second separation (2D). A three-step process converts the raw data into a format equivalent to a traditional GC×GC separation chromatogram: 1. signal differentiation, 2. inversion of data, 3. baseline correction. The first instrumental system (GC×GC-Flame Ionization Detector (FID) with a PM of 500 ms, separating a 115-component mixture composed of a wide range of boiling points (36–372 °C) compounds with apparent peak widths on the 2D, 2Wb, ranged from 10 to 40 ms, producing a 2D peak capacity, 2nc, of ~ 20, and the total peak capacity, nc,2D, was 7200 or a peak capacity production of 1200 peaks/min. For a PM of 75 ms, separating a low boiling point 15-component mixture isothermally, apparent peak widths on the 2D, 2Wb, averaged 10 ms producing a 2D peak capacity, 2nc, of ~ 7.5, with a peak capacity production of 950 peaks/min. The second system incorporated a high temperature diaphragm valve modulator and a pulse valve flow modulator to create a three-dimensional gas chromatography system (GC3) with a peak capacity production of 1000 peaks/min which is a ~5 times increase in efficiency compared to other GC3 systems. The third instrumental design established capability with a time-of-flight mass spectrometer (TOF), a method was developed for GC×GC-TOF separation in which a concentration study was conducted with an 18-component mixture and a PM of 50 ms. The subsequent data was deconvoluted with multivariate curve resolution-alternating least squares (MCR-ALS) in order to obtain their identification via match values. The resulting MCR-ALS data was converted in a similar manner as before into GC×GC chromatograms. Lastly, the pulse valve flow modulator was demonstrated to conduct continuous gas sampling of a system via one dimensional (1D) chromatography. The method applies the partial modulation technique to create frontal analysis peaks that are then transformed into a 1D chromatogram of analytes from a dynamic system that present a novel method of continuous sampling.
- Chemistry