Facilitating method development for reverse fill/flush flow modulation by using a tuneable auxiliary pressure source instead of a fixed bleed capillary.

The conventional reverse fill/flush flow modulation for comprehensive two-dimensional gas chromatography requires a bleed capillary column to be connected to the outlet of the modulator channel. The purpose of this capillary, which does not contain the stationary phase, is to provide pressure resistance to the modulator channel flow. In this way, the desired modulator volumetric flow can be achieved, and channel over-filling can be avoided. Normally, the length and the internal diameter of the bleed capillary are chosen so as to obtain the modulator flow that is close to the flow of the first separation column. Thus, for any chosen set of chromatographic conditions, the required dimensions of the bleed capillary can be completely different, making the two-dimensional gas chromatography method development tedious and generating additional costs in consumables and analyst time. In this work, a tuneable pressure source generating a suitable backpressure was used instead of the fixed bleed capillary which has the advantage of the possibility to freely adapt the pressure resistance and generate the required modulator channel flow for any conditions. This set-up has been evaluated and compared in terms of the impact on the modulation performance to the set-up involving a fixed bleed capillary demonstrating comparable performance.

Score Function for the Optimization of the Performance of Forward Fill/Flush Differential Flow Modulation for Comprehensive Two-Dimensional Gas Chromatography.

Modulation is the key element of the comprehensive 2D gas chromatography separation. Forward fill/flush flow modulation is cost effective, robust and suitable for analysis of a wide range of samples. Even though this modulation system is well known, studies regarding its optimization are sparse. In this work, based on hundreds of experiments involving multiple column sets and modulation conditions, an approach was proposed that permits to facilitate the choice of the forward fill/flush flow modulation parameters. A score function was developed that allows to predict the forward fill/flush flow modulation process efficiency as judged by the modulated peak shape. The score function was based on the physical rules for optimized and quantitative forward fill/flush flow modulation proposed in our previous work, which state that the sum of the fill and flush modulation distances should be close to the modulation channel length and that the ratio of the flush and fill distances should be sufficiently high for efficient channel flushing. The score function was embedded in a freely available tool in the form of a forward fill/flush flow modulation calculator, which allows the user either to quickly check the relevancy of the modulation operating conditions or to obtain a suggestion for optimal modulation parameters.

Advanced data preprocessing for comprehensive two-dimensional gas chromatography with vacuum ultraviolet spectroscopy detection.

Comprehensive two-dimensional gas chromatography with vacuum ultraviolet detection results in sizable data for which noise and baseline drift ought to be corrected. As the data is acquired from multiple channels, preprocessing steps have to be applied to the data from all channels while being robust and rather fast with respect to the significant size of the data. In this study, we have described advanced data preprocessing techniques for such data which were not available in the existing commercial software solutions and which were dedicated primarily to noise and baseline correction. Noise reduction was performed on both the spectral and the time dimension. For the baseline correction, a morphological approach based on iterated convolutions and rectifier operations was proposed. On the spectral dimension, much less noisy and reliable spectra were obtained. From a quantitative point of view, mentioned preprocessing steps significantly improved the signal-to-noise ratio for the analyte detection (circa six times in this study). These preprocessing methods were integrated into the plugim! platform (https://www.plugim.fr/).

Determination of vacuum ultraviolet detector response factors by hyphenation with two-dimensional comprehensive gas chromatography with flame ionization detection.

Two-dimensional comprehensive gas chromatography is an established technique, employed for the characterization of complex samples. Broadband vacuum ultraviolet absorption spectroscopy detection has recently attracted a lot of attention as it is a universal detection technique characterized by good selectivity but also ease of use and amenability to coupling with two-dimensional comprehensive gas chromatography. Vacuum ultraviolet spectroscopy is particularly interesting due to the possibility of performing spectral decomposition for species that coelute in gas chromatography analysis. This detector has quantitative capabilities, however not all species absorb vacuum ultraviolet radiation the same. Unfortunately, vacuum ultraviolet relative response factors for compounds are not always available. Methods to rapidly measure vacuum ultraviolet relative response factors and generate a large database that would allow calibration free quantitative analysis of complex mixtures are therefore of great interest. In this work, a universal methodology that permits rapid measurement of vacuum ultraviolet relative response factors is reported. It involves flow modulated two-dimensional comprehensive gas chromatography with dual vacuum ultraviolet and flame ionization detection. In this set-up, flame ionization detection is employed as a quantitative reference allowing to scale vacuum ultraviolet responses of investigated compounds. This approach was validated by flow measurements and by comparing relative response factors obtained for model compounds with literature data.

Quantitative performance of forward fill/flush differential flow modulation for comprehensive two-dimensional gas chromatography.

GC × GC is an advanced separation technique allowing to achieve quantitative and qualitative characterization of complex samples. In order to perform two-dimensional separation, the system must provide suitable peak modulation which will direct short impulses of first column flow towards the second column. Forward fill/ flush differential flow modulation is a cost effective and no cryogen requiring approach which allows modulation over a wide range of analytes with very different boiling points. However, optimization of the flow modulation process can be difficult to understand and quantification performance might be compromised if the parameters of the modulation process are not properly set. Modulated peak shape can be a good indication of the efficiency of the modulation process, however it is not sufficient to guarantee good quantification. Different average velocities in the beginning and the end of the thermally programmed GC run may cause different efficiency of the modulation process in various parts of the chromatogram. The purpose of this work is to investigate quantitative performance of the forward/fill flush modulation and delineate parameters that determine the effectiveness of the modulation process and its ability to properly reflect the quantitative composition of the investigated sample.

Gas chromatography vacuum ultraviolet spectroscopy: A review.

Accelerated technological progress and increased complexity of interrogated matrices imposes a demand for fast, powerful, and resolutive analysis techniques. Gas chromatography has been for a long time a 'go-to' technique for the analysis of mixtures of volatile and semi-volatile compounds. Coupling of the several dimensions of gas chromatography separation has allowed to access a realm of improved separations in the terms of increased separation power and detection sensitivity. Especially comprehensive separations offer an insight into detailed sample composition for complex samples. Combining these advanced separation techniques with an informative detection system such as vacuum ultraviolet spectroscopy is therefore of great interest. Almost all molecules absorb the vacuum ultraviolet radiation and have distinct spectral features with compound classes exhibiting spectral signature similarities. Spectral information can be 'filtered' to extract the response in the most informative spectral ranges. Developed algorithms allow spectral mixture estimation of coeluting species. Vacuum ultraviolet detector follows Beer-Lambert law, with the possibility of calibrationless quantitation. The purpose of this article is to provide an overview of the features and specificities of gas chromatography-vacuum ultraviolet spectroscopy coupling which has gained interest since the recent introduction of a commercial vacuum ultraviolet detector. Potentials and limitations, relevant theoretical considerations, recent advances and applications are explored.