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Highlights • New method for the analysis of exhaled breath VOCs by TD-GC × GC-FID/qMS. • Optimisation of flow modulation and dual detection alongside clinical requirements. • Addresses key challenges of using GC × GC for large-scale breath metabolomics. Abstract Precision medicine has spurred new innovations in molecular pathology leading to recent advances in the analysis of exhaled breath as a non-invasive diagnostic tool. Volatile organic compounds (VOCs) detected in exhaled breath have the potential to reveal a wealth of chemical and metabolomic information. This study describes the development of a method for the analysis of breath, based on automated thermal desorption (TD) combined with flow modulated comprehensive two-dimensional gas chromatography (GC×GC) with dual flame ionisation and quadrupole mass spectrometric detection (FID and qMS). The constrained optimisation and analytical protocol was designed to meet the practical demands of a large-scale multi-site clinical study, while maintaining analytical rigour to produce high fidelity data. The results demonstrate a comprehensive method optimisation for the collection and analysis of breath VOCs by GC×GC, integral to the standardisation and integration of breath analysis within large clinical studies. [ABSTRACT FROM AUTHOR]

The present research is focused on the use of a triple quadrupole mass spectrometer (QqQ MS) coupled with flow modulated comprehensive two-dimensional gas chromatography (FM GC × GC) for a multilevel elucidation of biodegradation potentiality of natural marine microbial populations during a bioremediation (biostimulation) treatment. The crude oil used for the evaluation of the bioremediation process, namely Dansk Blend Pier E1, represents a very complex sample. Hence, in order to understand the metabolic activity of microbial populations during the bioremediation process, a GC × GC system was used. The high separation power has allowed a detailed characterization of the different chemical families; moreover, thanks to the high acquisition frequency of the QqQ MS spectrometer, both full scan and multiple reaction monitoring (MRM) data were acquired in the same run. By using this system, both qualitative analysis of untargeted hydrocarbons mixture (crude oil) and qualitative analysis of biomarker compounds, present in low amount and often hindered under the bulk of the sample (i.e. adamantanes, diamantanes, steranes and hopanes), were performed simultaneously. The bioremediation capability of biostimulated bacteria was evaluated at four (T 4 ), eight (T 8 ) and fourteen (T 14 ) days. Progressive degradation of linear, branched, and aromatic hydrocarbons, adamantanes, and diamantanes has been showed, whereas, results underline the lack of any kind of activity against steranes, and hopanes. [ABSTRACT FROM AUTHOR]

The present paper is focused on the use of a vacuum ultraviolet absorption spectrometer (VUV) for gas chromatography (GC), within the context of flow modulated comprehensive two-dimensional gas chromatography (FM GC × GC). The features of the VUV detector were evaluated through the analysis of petrochemical and fatty acids samples. Besides responding in a predictable fashion via Beer’s law principles, the detector provides additional spectroscopic information for qualitative analysis. Virtually all chemical species absorb and have unique gas phase absorption features in the 120–240 nm wavelength range monitored. The VUV detector can acquire up to 90 full range absorption spectra per second, allowing its coupling with comprehensive two-dimensional gas chromatography. This recent form of detection can address specific limitations related to mass spectrometry ( e.g., identification of isobaric and isomeric species with very similar mass spectra or labile chemical compounds), and it is also able to deconvolute co-eluting peaks. Moreover, it is possible to exploit a pseudo-absolute quantitation of analytes based on pre-recorded absorption cross-sections for target analytes, without the need for traditional calibration. Using this and the other features of the detector, particular attention was devoted to the suitability of the FM GC × GC-VUV system toward qualitative and quantitative analysis of bio-diesel fuel and different kinds of fatty acids. Satisfactory results were obtained in terms of tailing factor (1.1), asymmetry factor (1.1), and similarity (average value 97%), for the FAMEs mixtures analysis. [ABSTRACT FROM AUTHOR]

The performances of forward flow fill and flush (FFF) and of reverse flow fill and flush (RFF) in flow modulated comprehensive two-dimensional gas chromatography (GC × GC) using the same volume of the sampling channel have been studied and compared. Sample models include a reference mixture of hydrocarbons at low concentration, a petroleum reformate product and the essential oil of Rosa damascena Miller. The latter samples contain solutes in different concentrations but some up to 30% allowing to study overloading phenomena in detail. For solutes injected at low quantity, the performance of FFF and RFF is similar. For solutes present in a sample at high quantity, RFF guarantees less broadening and spreading resulting in better quantitation. [ABSTRACT FROM AUTHOR]

The main objective of the herein described research was focused on performing satisfactory flow modulation (FM), in comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC–MS), using an MS-compatible second-dimension gas flow of approx. 4 mL min −1 . The FM model used was based on that initially proposed by Seeley et al. [3] . The use of limited gas flows was enabled through fine tuning of the FM parameters, in particular the duration of the re-injection (or flushing) process. Specifically, the application of a long re-injection period (i.e., 700 ms) enabled efficient accumulation-loop flushing with gas flows of about 4 mL min −1 . It was possible to apply such extended re-injection periods by using different restrictor lengths in the connections linking the modulator to the auxiliary pressure source. FM GC × GC–MS applications were performed on a mixture containing C 9–10 alkanes, and on a sample of essential oil. GC × GC–MS sensitivity was compared with that attained by using conventional GC–MS analysis, in essential oil applications. It was observed that signal intensities were, in general, considerably higher in the FM GC × GC–MS experiments. [ABSTRACT FROM AUTHOR]

The present research is based on the development and use of a flow-modulation (FM) comprehensive two-dimensional gas chromatography–quadrupole mass spectrometry (GC × GC–qMS) method for the determination of recently-highlighted (by the Scientific Committee on Consumer Safety) fragrance allergens (54) in cosmetics. FM GC × GC–qMS conditions were finely tuned to generate flow conditions (≈7 mL min −1 ) compatible with the qMS system used. Six-point calibration curves, over the range 1, 5, 10, 20, 50, 100 mg L −1 , were constructed for the 54 target allergens, with satisfactory linearity observed in all cases. Absolute quantification was performed by using extracted ions; target analyte identification was performed through measurement of ion ratios (qualifier/quantifier), full-scan MS database matching and the use of linear retention indices. Additional analytical figures of merit subjected to measurement were intra-day repeatability, accuracy at the 25 and 5 mg L −1 levels, and limits of detection and quantification. The number of data points per peak, along with mass spectral skewing, was also subjected to evaluation. Finally, the FM GC × GC–qMS method was used not only for the quantification of target allergens in five commercial perfumes, but also for general qualitative profiling. [ABSTRACT FROM AUTHOR]

Comprehensive two-dimensional gas chromatography (GC×GC) modulators normally transfer primary column effluent to the head of the secondary column as a series of sharp pulses. Such pulses are produced with time-varying temperature gradients in thermal modulation or with time-varying flow patterns in flow modulation. Thermal modulators produce narrow peaks at optimal flow rates, but require large amounts of consumables or a highly engineered heating/cooling system. Flow modulators involve simpler hardware and no additional consumables. However, flow modulators require a large increase in secondary column flow or transfer only a small portion of the primary effluent to the secondary column. This study examines a new method of producing GC×GC separations with a flow modulator. Instead of injecting narrow pulses, the modulator transfers primary effluent to the secondary column in the form of an intricate injection pattern. The detector signal is deconvoluted and converted to a two-dimensional chromatogram. The high duty cycle of the technique (>50%) leads to deconvoluted peaks with twenty times greater intensity than those produced by conventional modulation with a Deans switch modulator. Pattern modulation can be produced without requiring elevated carrier flows. This study evaluates the efficacy of pattern modulation GC×GC by analyzing a standard mixture of 43 oxygenated organic compounds and an E85 fuel sample. [ABSTRACT FROM AUTHOR]

The present research is focused on the use and evaluation of a novel helium ionization detector, defined as barrier discharge ionization detector (BID), within the context of (low-)flow modulation comprehensive two-dimensional gas chromatography (FM GC × GC). The performance of the BID device was compared to that of a flame ionization detector (FID), under similar FM GC × GC conditions. Following development and optimization of the FM GC × GC method, the BID was subjected to fine tuning in relation to acquisition frequency and discharge flow. Moreover, the BID performance was measured and compared to that of the FID, in terms of extra-column band broadening, sensitivity and dynamic range. The comparative study was carried out by using standard compounds belonging to different chemical classes, along with a sample of diesel fuel. Advantages and disadvantages of the BID system, also within the context of FM GC × GC, are critically discussed. In general, the BID system was characterized by a more limited dynamic range and increased sensitivity, compared to the FID. Additionally, BID and FID contribution to band broadening was found to be similar under the operational conditions applied. Particular attention was devoted to the behaviour of the FM GC × GC-BID system toward saturated and aromatic hydrocarbons, for a possible future use in the field of mineral-oil food contamination research. [ABSTRACT FROM AUTHOR]

The present research is focused on the development of a flow-modulated comprehensive two-dimensional gas chromatography–triple quadrupole mass spectrometry (FM GC × GC–MS/MS) method for the determination of classes of aromatic organic sulphur compounds (benzothiophenes, dibenzothiophenes, and benzonaphthothiophene) in heavy gas oil (HGO). The MS/MS instrument was used to provide both full-scan and multiple-reaction-monitoring (MRM) data. Linear retention index (LRI) ranges were used to define the MRM windows for each chemical class. Calibration solutions (internal standard: 1-fluoronaphthalene) were prepared by using an HGO sample, depleted of S compounds. Calibration information was also derived for the thiophene class (along with MRM and LRI data), even though such constituents were not present in the HGO. Linearity was satisfactory over the analyzed concentration range (1–100 mg/L); intra-day precision for the lowest calibration point was always below 17%. Accuracy was also satisfactory, with a maximum percentage error of 3.5% (absolute value) found among the S classes subjected to (semi-)quantification. The highest limit of quantification was calculated to be 299 μg/L (for the C1-benzothiophene class), while the lowest was 21 μg/L (for the C4-benzothiophene class). [ABSTRACT FROM AUTHOR]

The present research is specifically based on the use of greatly-reduced gas flows, in flow-modulator (FM) comprehensive two-dimensional gas chromatography systems. In particular, focus of the present research is directed to FM devices characterized by an accumulation stage, and a much briefer re-injection step. It has been widely accepted that the operation of such FM systems requires high gas flows (≥20 mL/min), to re-inject the gas-phase contents of sample (or accumulation) loops, onto the second column. On the contrary, it will be herein demonstrated that much lower gas flows (≈ 6–8 mL/min) can efficiently perform the modulation step of re-injection. The possibility of using such improved operational conditions is given simply by a fine optimization of the processes of accumulation and re-injection. The application of lower gas flows not only means that second-dimension separations are carried out under better analytical conditions, but, even more importantly, greatly reduces problems which arise when using mass spectrometry (i.e., sensitivity and instrumental pumping capacity). [ABSTRACT FROM AUTHOR]

Highlights: [•] A high-speed Deans switch has been constructed using commercially available components. [•] The Deans switch was optimized for use as a low duty cycle GC×GC modulator. [•] The modulator produces narrow pulses without requiring large secondary column flows. [ABSTRACT FROM AUTHOR]

Abstract: Comparison of conventional one-dimensional gas chromatography (1D-GC) and comprehensive two-dimensional gas chromatography (GC×GC) shows that the detector signal in GC×GC is significantly enhanced. The value of this enhancement depends on the operating parameters, such as the modulation time and the non-modulated (1D column) and corresponding modulated (2D column) peak widths. Determination of the enhance factors in flow modulated GC×GC for separation of hydrocarbon samples using flame ionization detection (FM GC×GC-FID) was studied. A term named detector response enhance factor (DREF) has been designed to express the value of the signal enhancement. Two methods were used to calculate DREF: (i) employing 2D peak height, and (ii) using a theoretical approach. Comparison of FM GC×GC-FID and 1D-GC-FID method illustrates that the DREF increases from 10 to 33 times, in 1–6s modulation time intervals. [Copyright &y& Elsevier]

Abstract: Flow-modulated comprehensive two-dimensional gas chromatography with simultaneous monitoring of the separation by flame ionization (GC×GC-FID) and quadrupole mass spectrometric (GC×GC-qMSD) detection was studied for the analysis of gasoline and kerosene samples. The acquisition frequency of the FID was 100Hz and of the qMSD 18Hz for the mass range m/z 40–300. The instrumental set-up is such that both one-dimensional (GC-FID and GC-qMSD) and two-dimensional separations using the same working conditions can be performed. Gasoline and kerosene samples were analyzed on the column combination HP-5MS (1D)+HP INNOWax (2D). Three modulated peaks were obtained for each hydrocarbon present above 0.1% with ca. 300ms peak width at the base using 6 s modulation times. Modulated peaks in GC×GC-FID were thus characterized by ca. 30 points while those in GC×GC-qMSD method by 6–8 points only. The FID speed is sufficient for reliable quantitative analysis, while the qMSD scan speed is perfectly appropriate for identification purposes. Moreover, in the GC×GC-qMSD method considerably improved quality of uncorrected spectra was obtained, arising from the enhanced separation over one-dimensional GC-MSD analysis. Spectral match qualities of up to 98% were found. [Copyright &y& Elsevier]

Abstract: The present manuscript is focused on the evaluation of a novel high-speed triple quadrupole mass spectrometer (QqQ MS), carried out under extreme GC conditions, namely those generated by a flow-modulated (FM) comprehensive two-dimensional GC (GC×GC) system. The novel QqQ MS system is capable of operation under high speed conditions, in both full-scan (maximum scan speed: 20,000amu/s) and multiple reaction monitoring (MRM) modes. Moreover, the QqQ MS instrument can generate simultaneous full scan/MRM data, also in a very rapid manner. An FM GC×GC–MSMS method was developed for the simultaneous full-scan qualitative analysis of untargeted essential oil compounds, and MRM quali/quantitative analysis of targeted ones, namely three preservatives [o-phenylphenol (OPP), butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA)]. The QqQMS system generated a sufficient number of data points per peak, for both qualitative and quantitative purposes. The degree of sensitivity, reached through the MRM analysis, widely exceeded current-day regulations. Method validation, related to the MRM analysis, was performed considering retention time, peak area and ion ratio repeatability, limits of detection and quantification, and accuracy. Additionally, a spearmint essential oil was spiked with 5 phytosanitary compounds at the 1ppb level, and analysed through an MRM-only GC×GC–MSMS application. Emphasis was devoted not only on sensitivity (satisfactory for all the contaminants), but also on the importance of precursor ion selection, and of the GC×GC separation process. Finally, sensitivity was compared between the MRM and SIM modes, in scan/MRM, MRM, scan/SIM and SIM analyses, performed on a mixture of 22 phytosanitary products, at a concentration level in the 50–150ppb range. [Copyright &y& Elsevier]

Abstract: The present investigation is focused on the development of a flow-modulator (FM) comprehensive 2D GC (GC×GC)-quadrupole mass spectrometry (qMS) approach, for the analysis of fatty acids. A recently developed flow modulator interfaced an apolar–polar column set, and was used for the first time with a mass spectrometer. Method development was achieved by using a standard mixture, containing fatty acid methyl esters (FAMEs). The total run time was approx. 40min, thus relatively rapid. The optimized FM GC×GC–qMS method was applied to marine and biological FAMEs. Validation parameters such as intra-day and inter-day repeatability, limits of identification (mass spectral quality was evaluated at various FAME concentrations), and quantification were measured. Peak assignment was performed using pure standard compounds (when available), linear retention indices (LRIs), a dedicated FAME MS database, and specific bidimensional chromatogram positions. The MS database contained one-dimensional LRI information, exploited as a filter during the MS database search procedure. A good agreement was observed between database LRI values, and those calculated on the twin-column set. The FM GC×GC–qMS method can be considered as a valid counterpart, with respect to cryogenically modulated GC×GC, in the fatty acid field of research. [Copyright &y& Elsevier]

Abstract: The present investigation is focused on a simple flow modulator (FM), for comprehensive two-dimensional gas chromatography (GC×GC). The interface is stable at high temperatures, and consists of a metallic disc (located inside the GC oven) with seven ports, which are connected to an auxiliary pressure source via two branches, to the first and second dimension, to a waste branch (linked to a needle valve) and to an exchangeable modulation loop (2 ports). The ports are connected via micro-channels, etched on one of the inner surfaces of the disc. Modulation is achieved using a two-way electrovalve, connected on one side to the additional pressure source, and to the two metal branches, on the other. An FM enantio-GC×polar-GC method (using a flame ionization detector) was optimized (a 40-μL loop was employed), for the analysis of essential oils. As an example, an application on spearmint oil is shown; the method herein proposed was subjected to validation. Finally, an FM GC×GC diesel experiment was carried out, using an apolar–polar column combination, to demonstrate the effectiveness of the modulator in the analysis of a totally different sample-type. [Copyright &y& Elsevier]

Abstract: Ionic liquid stationary phases were tested for one dimensional gas chromatography–mass spectrometry (GC–MS) and comprehensive two dimensional gas chromatography (GC×GC) of fatty acid methyl esters from algae. In comparison with polyethylene glycol and cyanopropyl substituted polar stationary phases, ionic liquid stationary phases SLB-IL 82 and SLB-IL 100 showed comparable resolution, but lower column bleeding with MS detection, resulting in better sensitivity. The selectivity and polarity of the ionic liquid phases are similar to a highly polar biscyanopropyl-silicone phase (e.g. HP-88). In GC×GC, using an apolar polydimethyl siloxane×polar ionic liquid column combination, an excellent group-type separation of fatty acids with different carbon numbers and number of unsaturations was obtained, providing information that is complementary to GC–MS identification. [Copyright &y& Elsevier]

Abstract: Comprehensive two-dimensional gas chromatography (GC×GC) offers an interesting tool for profiling bacterial fatty acids. Flow modulated GC×GC using a commercially available system was evaluated, different parameters such as column flows and modulation time were optimized. The method was tested on bacterial fatty acid methyl esters (BAMEs) from Stenotrophomonas maltophilia LMG 958T by using parallel flame ionization detector (FID)/mass spectrometry (MS). The results are compared to data obtained using a thermal modulated GC×GC system. The data show that flow modulated GC×GC-FID/MS method can be applied in a routine environment and offers interesting perspectives for chemotaxonomy of bacteria. [Copyright &y& Elsevier]

Abstract: Flow modulation of methane-doped carrier gas is used to visualize the second dimension hold-up time in GC×GC continuously throughout the run. This provides an internal reference of hold-up time and presents a straightforward means of examining retention in each dimension of GC×GC. Retention factors on similar and dissimilar column pairs are examined. Stationary phase bleed is shown to be retained by the second dimension column. [Copyright &y& Elsevier]

Abstract: Pulsed flow modulation (PFM) is based on higher flow rate time compression of the first GC column effluent, which prior to the injection into the second column is stored for a few seconds in a standard fused silica wide bore transfer line. We constructed the PFM device with two standard 1/16in. brass compression fittings with the insertion of the two columns inside the wide bore 0.53mm i.d. fused silica storage transfer line for the elimination of dead volumes. This simple arrangement provides a combination of flexibility in the length of the sample storage transfer line hence comprehensive two-dimensional gas chromatography (GC×GC) cycle time, inert sample path and full elimination of cooling gas consumption. A record short second column injection time of 20ms is demonstrated. Practical injection times are the sample collection time (such as 4s) divided by the second to first column flow rate ratio (such as 20/0.7), which is typically around 150ms. Due to the low cost of the device it can also be considered for use with non comprehensive time segmented GC×GC to remove a few accidental coelutions. PFM-GC×GC excels with high second column capacity due to the use of 0.32mm i.d. columns with high flow rates as the second dimension GC×GC column. As a result, PFM-GC×GC can have up to two orders of magnitude higher second column sample capacity and linear dynamic range for improved reduction of adverse matrix interference effects due to column overloading. [Copyright &y& Elsevier]

Abstract: A new approach of flow modulation comprehensive two-dimensional gas chromatography–mass spectrometry (GC×GC–MS) with supersonic molecular beam (SMB) and a quadrupole mass analyzer is presented. Flow modulation uniquely enables GC×GC–MS to be achieved even with the limited scan speed of quadrupole MS, and its 20ml/min column flow rate is handled, splitless, by the SMB interface. Flow modulation GC×GC–SMB–MS shares all the major benefits of GC×GC and combines them with GC–MS including: (a) increased GC separation capability; (b) improved sensitivity via narrower GC peaks; (c) improved sensitivity through reduced matrix interference and chemical noise; (d) polarity and functional group sample information via the order of elution from the second polar column. In addition, GC×GC–SMB–MS is uniquely characterized by the features of GC–MS with SMB of enhanced and trustworthy molecular ion plus isotope abundance analysis (IAA) for improved sample identification and fast fly-through ion source response time. The combination of flow modulation GC×GC with GC–MS with SMB (supersonic GC–MS) was explored with complex matrices such as diesel fuel analysis and pesticide analysis in agricultural products. [Copyright &y& Elsevier]

• A novel low-duty cycle flow modulator (FM) has been evaluated • Focus was devoted to the advisable operational conditions of the FM • Two different GC × GC column sets were used • A fast FM GC × GC-ToFMS method was developed for the analysis of cosmetic allergens The present research is focused on the preliminary evaluation, in particular in relation to the advisable operational conditions, of a novel low duty cycle flow modulator. In such a respect, a fast comprehensive two-dimensional gas chromatography-mass spectrometry method is herein proposed. Applications on a C 7 -C 30 series of alkanes, 64 fragrance allergens (plus 2 internal standards), and 5 perfumes, were carried out by using two different column sets, low-polarity + medium-polarity and low-polarity + low-polarity. In both cases, the first column was of dimensions 10 m × 0.25 mm ID × 0.25 µm d f , while the second one was of dimensions 1 m × 0.10 mm ID × 0.10 µm d f. A modulation period of 700 ms, with a re-injection period of 80 ms, was used in order to obtain a higher duty cycle (measured to be approx. 0.04). Absolute quantification of the allergens was carried out by using two internal standards, namely 1,4-dibromobenzene and 4,4'-dibromobiphenyl. In terms of limits of quantification the instrumental response was characterized by a wide variability, ranging between 9 ppb and 5.4 ppm for both column sets. A total number of 97 fragrance allergens were identified and quantified in five commercial perfumes. [ABSTRACT FROM AUTHOR]

• Low flow conditions are employed with flow modulation. • Dynamic pressure gradient modulation in full modulation mode is utilized. • Fully modulated peaks provide enhanced signal and low limit of detection. • The evaluation of the quality of the data using chemometric tools is provided. • Decomposition of poorly resolved analytes at low concentration was successful. Dynamic pressure gradient modulation (DPGM) is investigated for comprehensive two-dimensional gas chromatography (GC × GC) with time-of-flight mass spectrometry (TOFMS) detection. With DPGM, a commercial pneumatic "pulse" valve is opened to introduce a suitably high auxiliary gas pressure at a T-junction connecting the first dimension (1D) and second dimension (2D) columns during the modulation period (P M), temporarily stopping the 1D flow. The valve is then closed for the duration of a pulse width (p w) to "re-inject" temporally focused 1D eluate onto the 2D column for separation. This flow modulation technique is observed to be compatible with TOFMS detection using a 2D flow rate of 4 ml/min for the separation of a 90-component test mixture. A 25 min separation window using a P M = 1 s and p w = 200 ms for full modulation (and 100% duty cycle) provided an average 1 W b = 4.5 s and 2 W b = 130 ms for a 2D peak capacity of n c,2D = 2700 (100 peaks per min). The detector response enhancement factor (DREF) serves as a metric for the enhanced sensitivity of the modulated relative to the unmodulated 1D peaks, with DREFs ranging between 10 and 20 and about a 5-fold improvement in signal-to-noise ratio (S / N). The bilinear "quality" of the GC × GC data is studied using the chemometric method parallel factor analysis (PARAFAC). Since PARAFAC requires sufficiently trilinear data, the reproducibility of the 2D peak shape for a given analyte is confirmed using lack-of-fit (LOF) and percent variation (R 2) metrics. The limit-of-detection (LOD) for the representative analyte hexadecane is determined using PARAFAC, providing an LOD of 0.7 ppb (±0.03 ppb) for three replicates. Seven heavily overlapped analytes are also fully resolved by PARAFAC down to the part-per-million (ppm) concentration level, producing reproducible spectra with a majority of spectral match values (MV) over 800 (RSD ≤ 7.1%). This study provides promising results for DPGM as a flow modulation technique compatible with GC × GC-TOFMS, providing high sensitivity data suitable for chemometric analysis. [ABSTRACT FROM AUTHOR]

A fluidic device called the multi-mode modulator (MMM) has been developed for use as a comprehensive two-dimensional gas chromatography (GC x GC) modulator. The MMM can be employed in a wide range of capacities including as a traditional heart-cutting device, a low duty cycle GC x GC modulator, and a full transfer GC x GC modulator. The MMM is capable of producing narrow component pulses (widths <50ms) while operating at flows compatible with high resolution chromatography. The sample path of modulated components is confined to the interior of a joining capillary. The joining capillary dimensions and the position of the columns within the joining capillary can be optimized for the selected modulation mode. Furthermore, the joining capillary can be replaced easily and inexpensively if it becomes fouled due to sample matrix components or column bleed. The principles of operation of the MMM are described and its efficacy is demonstrated as a heart-cutting device and as a GC x GC modulator., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The present paper contains research data relative to an approach herein defined as flow-modulation (FM) low-pressure comprehensive two-dimensional gas chromatography, abbreviated as "GC×LP GC". The abbreviation LP is positioned before the second GC abbreviation because LP conditions were generated across a mega-bore second-dimension column (10m×0.53mm ID), it being connected to a quadrupole mass spectrometer (qMS). Flow modulation was performed with MS-compatible gas flows (7-8mL/min), following recent research work [7]; using such an approach, the main disadvantage of flow modulation, specifically the generation of excessively high second-dimension flows, is avoided. A further noteworthy aspect of the investigation was the use of a long accumulation loop (e.g., 51cm), a modification that greatly improved the general post-modulation peak shape quality. FM GC×LP GC-qMS applications on pure standard compounds, as well as on milk and fish oil fatty acid methyl esters, are shown and discussed., (Copyright © 2014 Elsevier B.V. All rights reserved.)