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The solid-state-modulator is a consumable-free thermal modulator, used within the context of comprehensive two-dimensional gas chromatography. Its consumable-free nature is guaranteed by the presence of a thermal-electric cooler device located between two heated chambers, everything located outside the gas chrpmatograph oven. The aim of the present research is to evaluate the solid-state-modulator modulation performance in relationship to different modulation capillary geometries. For this purpose, two coated modulation capillaries with the same length, but with different internal diameters (0.25 and 0.18 mm) were used. The effects of gas linear velocity, modulator temperature, and modulation period were evaluated in several applications involving standard alkanes and a sample of diesel fuel. Fundamental gas chromatography parameters (peaks widths, resolution) were measured under the different experimental conditions. Detailed information is provided on gas flow optimization, with particular emphasis on the efficiency of chromatography band reinjection onto the second-dimension column. The results obtained from the present investigation highlight how the modulation capillary characteristics have a great impact on the overall comprehensive two-dimensional gas chromatography separation. Specifically, considering the results herein attained, the use of a 0.18 mm ID × 0.18 μm df modulation column is advisable compared to a 0.25 mm ID × 0.25 μm df one.

A single-channel comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry (GCxGC-qMS) system was developed using a recently introduced solid-state thermal modulator. By modulation on a special column, extremely light hydrocarbons down to C2 can be successfully modulated without use of any cryogens. Paired with a polar secondary dimension column, a hybrid primary dimension column was developed to provide complete two-dimensional separation of all target volatile organic compounds (VOCs) from C2 to C12. This single-channel GCxGC-qMS system is used to analyze VOC standards containing 57 PAMS and 64 TO-15 gas mixtures, as well as real-world samples. This study demonstrates that a low resource GCxGC-qMS system may serve as a feasible tool for routine VOCs monitoring.

We introduce an information rich analytical approach called parallel comprehensive two-dimensional gas chromatography (2GC × 2GC). This parallel chromatography approach splits injected samples into two independent two-dimensional column ensembles and provides two GC × GC separations by using contra-directional thermal modulation. The first-dimension (1D) and second-dimension (2D) columns are connected using planar three-port microchannel devices, which are supplied with supplementary flow via two pressure controller modules. Precise carrier gas flow control at the junction of the 1D and 2D columns permits independent control of flow conditions in each separation column. The 2GC × 2GC approach provides two entirely independent GC × GC separations for each injection. Analysis of hop (Humulus lupulus L.) essential oils is used to demonstrate the capability of the approach. The analytical performance of each GC × GC separation in the 2GC × 2GC experimentis comparable to individual GC × GC separation with matching column configurations. The peak capacity of 2GC × 2GC is about 2 times than that of single GC × GC system. The dual 2D chromatograms produced by this single detector system provide complementary separations and additional identification information by harnessing different selectivity provided by the four separation columns.

Comprehensive two-dimensional gas chromatography (GC×GC) based on flow-modulation (FM) is gaining increasing attention as an alternative to thermal modulation (TM), the recognized GC×GC benchmark, thanks to its lower operational cost and rugged performance. An accessible, rational procedure to perform method translation between the two platforms would be highly valuable to facilitate compatibility and consequently extend the flexibility and applicability of GC×GC. To enable an effective transfer, the methodology needs to ensure preservation of the elution pattern, separation power, and sensitivity. Here, a loop-type thermal modulation system with dual detection (TM-GC×GC-MS/FID) used for the targeted analysis of allergens in fragrances is selected as reference method. Initially, six different columns configurations are systematically evaluated for the flow-modulated counterpart. The set-up providing the most consistent chromatographic separation (20 m x 0.18 mm dc x 0.18 μm df + 1.8 m x 0.18 mm dc x 0.18 μm df) is further evaluated to assess its overall performance in terms of sensitivity, linearity, accuracy, and pattern reliability. The experimental results convincingly show that the method translation procedure is effective and allows successful transfer of the target template metadata. Additionally, the FM-GC×GC-MS/FID system is suitable for challenging applications such as the quantitative profiling of complex fragrance materials.

Designing a high-performance a micro-fabricated thermal modulator ( $\mu $ TM) is critical for realizing a portable comprehensive microscale 2-D gas chromatography ( $\mu $ GC $\times \mu $ GC) system. However, there is little fundamental understanding of the physics governing two-stage thermal modulation. Toward that goal, we perform finite element and analytical modeling based on convection-diffusion equations and obtain excellent match with experimental results. We demonstrate that unlike bench-top TMs, species are not immobile during the trapping phase of modulation. A 10% decrease in time-constant of the first stage improves peak capacity of $\mu $ GC $\times \mu $ GC, full-width-at-half-height of the modulated peak proportionately, and reduces breakthrough by ~70%. Due to the high cost of micro-fabrication, it is prohibitively expensive to perform such studies experimentally. Performing design optimizations numerically using such models could lead to the realization of portable $\mu $ GC $\times \mu $ GC systems and low-cost bench-top $\mu $ TMs. We conclude by suggesting some possible improvements to our $\mu $ TM design. [2016-0296]

The present research is based on the use of a recently developed comprehensive two-dimensional gas chromatography thermal modulator, which is defined as solid-state modulator. The transfer device was installed on top of a single gas chromatography oven, while benchtop low-resolution time-of-flight mass spectrometry was used to monitor the compounds exiting the second analytical column. The solid-state modulator was first described by Luong et al. in 2016, and it is a moving modulator that does not require heating and cooling gases to generate comprehensive two-dimensional gas chromatography data. The accumulation and remobilization steps occur on a trapping capillary, this being subjected to thermoelectric cooling and micathermic heating. In this study, the effects of the gas linear velocity on the modulation performance were evaluated by using two different uncoated trapping capillaries, viz., 0.8 m × 0.25 mm id and 0.8 m × 0.20 mm id. Solid-state modulator applications were carried out on a standard solution containing n-alkanes (C9, C10, C12 ), and on a sample of diesel fuel. The results indicated that the type of trapping capillary and gas velocity have a profound effect on modulation efficiency.

Comprehensive two-dimensional liquid chromatography (LC × LC) allows for substantial gains in theoretical peak capacity in the field of liquid chromatography. However, in practice, theoretical performance is rarely achieved due to a combination of undersampling, orthogonality, and refocusing issues prevalent in many LC × LC applications. This is intricately linked to the column dimensions, flow rates, and mobile-phase compositions used, where, in many cases, incompatible or strong solvents are introduced in the second-dimension ( 2D) column, leading to peak broadening and the need for more complex interfacing approaches. In this contribution, the combination of temperature-responsive (TR) and reversed-phase (RP) LC is demonstrated, which, due to the purely aqueous mobile phase used in TRLC, allows for complete and more generic refocusing of organic solutes prior to the second-dimension RP separation using a conventional 10-port valve interface. Thus far, this was only possible when combining other purely aqueous modes such as ion exchange or gel filtration chromatography with RPLC, techniques which are limited to the analysis of charged or high MW solutes, respectively. This novel TRLC × RPLC combination relaxes undersampling constraints and complete refocusing and therefore offers novel possibilities in the field of LC × LC including temperature modulation. The concept is illustrated through the TRLC × RPLC analysis of mixtures of neutral organic solutes.

The applicability of comprehensive two-dimensional gas chromatography (GC×GC) using a single-stage thermal modulator was explored for the analysis of honeybush tea (Cyclopia spp.) volatile compounds. Headspace solid phase micro-extraction (HS-SPME) was used in combination with GC×GC separation on a non-polar × polar column set with flame ionisation (FID) detection for the analysis of fermented Cyclopia maculata, Cyclopia subternata and Cyclopia genistoides tea infusions of a single harvest season. Method optimisation entailed evaluation of the effects of several experimental parameters on the performance of the modulator, the choice of columns in both dimensions, as well as the HS-SPME extraction fibre. Eighty-four volatile compounds were identified by co-injection of reference standards. Principal component analysis (PCA) showed clear differentiation between the species based on their volatile profiles. Due to the highly reproducible separations obtained using the single-stage thermal modulator, multivariate data analysis was simplified. The results demonstrate both the complexity of honeybush volatile profiles and the potential of GC×GC separation in combination with suitable data analysis techniques for the investigation of the relationship between sensory properties and volatile composition of these products. The developed method therefore offers a fast and inexpensive methodology for the profiling of honeybush tea volatiles. Graphical abstract Surface plot obtained for the GC×GC-FID analysis of honeybush tea volatiles.

Longitudinal on-column thermal modulation for comprehensive two-dimensional liquid chromatography is introduced. Modulation optimization involved a systematic investigation of heat transfer, analyte retention, and migration velocity at a range of temperatures. Longitudinal on-column thermal modulation was realized using a set of alkylphenones and compared to a conventional valve-modulator employing sample loops. The thermal modulator showed a reduced modulation-induced pressure impact than valve modulation, resulting in reduced baseline perturbation by a factor of 6; yielding a 614-fold improvement in signal-to-noise. A red wine sample was analyzed to demonstrate the potential of the longitudinal on-column thermal modulator for separation of a complex sample. Discrete peaks in the second dimension using the thermal modulator were 3055% narrower than with the valve modulator. The results shown herein demonstrate the benefits of an active focusing modulator, such as reduced detection limits and increased total peak capacity. Refereed/Peer-reviewed

Experiments in the development of two prototype interfaces for comprehensive multidimensional gas chromatography (GC x GC) have demonstrated some interesting aspects of the interface design that must be considered as researchers try to develop better interface technologies based upon thermal modulation. Studies of injection band structure from cryotrap-based and sorbent-based interfaces demonstrated the effects of cooling times and applied heating pulses on the performance of the interfaces. Additionally, effects of non-optimised positioning of the cryogen addition point for cryogenic interfaces are discussed. Results from direct measurements of Silco-steel cooling times correlated well with breakthrough tails seen in single-stage cryotraps, suggesting that tubing with smaller thermal mass (hence faster cooling times) should perform better when incorporated into the system.

Article, Analytical sciences : the international journal of the Japan Society for Analytical Chemistry. 17(8):991-994 (2001)

Electroabsorption spectra have been measured for undoped C 60 thin films at 80 and 300 K in the spectral range 1.76 to 5 eV. Absorption and thermal modulation spectra have also been obtained. The electronic energy levels of C 60 are reviewed, and the electroabsorption spectra are discussed in terms of the Stark effect on energy levels of A g , H g and T u symmetries.

Comprehensive three-dimensional gas chromatography (GC') is demonstrated using modified GC x GC apparatus. A new thermal modulation scheme employing a single moving heater to operate two thermal modulators is introduced. Considerations of the bandwidth/ resolution tradeoff of GC 3 show that high-speed tertiary columns would make GC3 practical, with modest loss of underlying GC x GC peak capacity.

Un modulateur thermique, utilise comme interface pour le couplage extraction avec un fluide supercritique ― chromatographie a fluide supercritique, est presente et teste. Le modulateur est chauffe a l'aide d'un courant electrique

Differential extended X-ray absorption fine structure (DiffEXAFS) is a novel technique for the study of small atomic strains. Here the development of this technique to the measurement of thermally induced strain is presented. Thermal DiffEXAFS measurements have been performed on alpha-Fe and SrF(2), yielding alpha = (11.6 +/- 0.4) x 10(-6) K(-1) and (19 +/- 2) x 10(-6) K(-1), respectively. These are in good agreement with accepted values, proving the viability of the technique. Analysis has revealed sensitivity to mean atomic displacements of 0.3 fm.

We have developed temperature-pulse microscopy in which the temperature of a microscopic sample is raised reversibly in a square-wave fashion with rise and fall times of several ms, and locally in a region of approximately 10 μm in diameter with a temperature gradient up to 2°C/μm. Temperature distribution was imaged pixel by pixel by image processing of the fluorescence intensity of rhodamine phalloidin attached to (single) actin filaments. With short pulses, actomyosin motors could be activated above physiological temperatures (higher than 60°C at the peak) before thermally induced protein damage began to occur. When a sliding actin filament was heated to 40–45°C, the sliding velocity reached 30 μm/s at 25 mM KCl and 50 μm/s at 50 mM KCl, the highest velocities reported for skeletal myosin in usual in vitro assay systems. Both the sliding velocity and force increased by an order of magnitude when heated from 18°C to 40–45°C. Temperature-pulse microscopy is expected to be useful for studies of biomolecules and cells requiring temporal and/or spatial thermal modulation.

Thermal modulation spectroscopic techniques have been developed to study the optical properties of copper complexes of spermine and spermidine. Both pure and mixed solutions of the complexes were used to prepare films on special substrate heaters. Measurement techniques were developed to obtain approximately quantitative estimates of the composition of the mixed films from the modulation spectra. It is concluded that modulation spectroscopy is an appropriate tool for obtaining quantitative information on biologically important compounds. The spectra at 77 K and 300 K were significantly different.

Measurements are described of the effects of applied electric fields on the delocalised exciton spectra which comprise the direct absorption edge in 2H-MoS2 (77 K). The field-modulated transmission spectrum is predominantly due to thermal modulation of the illuminated crystal, but when this is reduced, field ionisation of the exciton states is observed at predicted field strengths. Es werden Messungen der Einfusse eines auseren elektrischen Feldes auf die Spektren delokalisierter Exzitonen, die die direkte Absorptionskante in 2H-MoS2 (77 K) einschliesen, beschrieben. Das feldmodulierte Transmissionsspektrum wird hauptsachlich durch die thermische Modulation des belichteten Kristalls hervorgerufer., wenn jedoch diese reduziert wird, wird Feldionisierung der Exzitonenzustande bei den vorhergesagten Feldstarken beobachtet.

The thermally modulated reflectance spectrum of gold has been measured over the range 1.8-3.2 eV, at 107 and 323K. A shift of +0.050+or-0.004 eV in the position of the principal peak at 2.5 eV in the Delta epsilon i spectrum has been observed as the temperature decreases, which is in agreement with the shift observed in wavelength modulated spectra. A corresponding shift of -0.075 eV in the subsidiary peak at 2.95 eV has also been observed. The results are discussed in the light of Christensen and Seraphin's (1971) band calculations and a possible alternative transition assignment suggested for the peak at 2.95 eV.

Studies of the low field (Hrms