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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 design of bioinspired systems for chemical sensing is an engaging line of research in machine olfaction. Developments in this line could increase the lifetime and sensitivity of artificial chemo-sensory systems. Such approach is based on the sensory systems known in live organisms, and the resulting developed artificial systems are targeted to reproduce the biological mechanisms to some extent. Sniffing behaviour, sampling odours actively, has been studied recently in neuroscience, and it has been suggested that the respiration frequency is an important parameter of the olfactory system, since the odour perception, especially in complex scenarios such as novel odourants exploration, depends on both the stimulus identity and the sampling method. In this work we propose a chemical sensing system based on an array of 16 metal-oxide gas sensors that we combined with an external mechanical ventilator to simulate the biological respiration cycle. The tested gas classes formed a relatively broad combination of two analytes, acetone and ethanol, in binary mixtures. Two sets of low-frequency and high-frequency features were extracted from the acquired signals to show that the high-frequency features contain information related to the gas class. In addition, such information is available at early stages of the measurement, which could make the technique suitable in early detection scenarios. The full data set is made publicly available to the community. 1 1 http://archive.ics.uci.edu/ml/datasets/Gas+sensor+array+under+flow+modulation . [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]

Siphonic roof drainage systems are an efficient method of removing rainwater rapidly from roofs. Siphonic roof drainage systems are designed to run full-bore, resulting in sub-atmospheric system pressures, higher driving heads and higher system flow velocities. Hence, siphonic roof drainage systems normally require far fewer downpipes, and the depressurised conditions also mean that much of the collection pipework can be routed at high level, thus reducing the extent of any underground pipework. But, they work properly at only one roof run-off rate and therefore suffer from sizing and operational problems that limit their performance. Climate change is creating situations where normal ranges of rainfall intensity are being frequently exceeded, and this may have an impact on the performance of siphonic roof drainage systems. A multiple parallel pipe siphonic roof drainage system appears to offer benefits and avoids sizing problems associated with current siphonic roof drainage systems. A movable cap covering the inlet to a small bank of parallel pipes has the potential to avoid noise associated with making and breaking siphonic action through flow modulation. Laboratory scale tests demonstrate the basic feasibility of the multiple parallel pipe system and indicate that handover of flow between pipes occurs smoothly and that the flow modulation cap functions reliably. This technology includes moving parts and smaller diameters (19 mm ID) than are currently accepted (32 mm ID) in the British Standards and product development will be required.Practical application: Original research detailing an innovative development of a multi-pipe siphonic roof drainage system. This provides a wide design flow rate range and flow modulation caps reduce noise significantly by avoiding priming failure. Potentially extends the technique to a smaller building size than with current siphonic systems and offers climate change resilience potential. [ABSTRACT FROM PUBLISHER]

Purpose: To evaluate endovascular repair of type II and III thoracoabdominal aortic aneurysms (TAAA) using the Multilayer Flow Modulator (MFM) in patients with contraindications for open surgery and fenestrated stent-grafts. Methods: In this prospective, multicenter, nonrandomized trial (EudraCT registration: 2009-013678-42; ClinicalTrials.gov identifier NCT01756911), 23 patients (19 men; mean age 75.8 years) with Crawford type II (43.5%) and III (56.5%) TAAA (mean diameter 6.5 cm) were treated with the MFM between April 2010 and February 2011. The primary efficacy outcome measure was stable aneurysm thrombosis with associated branch vessel patency at 12 months; the primary safety endpoint was 30-day and 12-month all-cause mortality. Results: The rate of technical success was 100%. In 20 patients with computed tomography scans at 12 months, the primary efficacy outcome was met in 15 patients. The rate of primary patency of covered branch vessels was 96% (53/55); 1 patient with 2 occluded visceral branches underwent successful surgical reintervention. Endoleaks were identified in 5 patients (3 attachment site and 2 at device overlap), 4 of whom underwent reintervention (3 additional MFMs and 1 stent-graft implanted). At 12 months, aneurysm diameter was stable in 18 of 20 patients; the mean ratio of residual aneurysm flow volume to total volume had decreased by 28.9%, and the mean ratio of thrombus volume to total lumen volume had increased by 21.3% (n=17). There were no cases of device migration, loss of device integrity, spinal cord ischemia, or aneurysm rupture. Conclusion: At 1 year, endovascular repair with the MFM appears to be safe and effective while successfully maintaining branch vessel patency. Follow-up is ongoing. [ABSTRACT FROM AUTHOR]

The present contribution is focused on the measurement of the analytical sensitivity attained in untargeted/targeted MS/MS experiments, performed using flow-modulator comprehensive 2D and 1D GC. The comprehensive 2D experiment was performed by diverting part of the high flow (circa 80%) to flush the accumulation loop (about 28 mL/min) to waste, to reduce the gas flow entering the ion source. 1D analyses were performed through: (i) unmodulated and (ii) single column applications. An equivalent temperature program was applied in the modulated and unmodulated analyses, while a faster one was employed in the single column one. In all application types, the (same) triple quadrupole instrument was operated in the full-scan and multiple reaction monitoring modes. A genuine sweet orange oil and the same sample spiked with 20 phytosanitary compounds were employed to reach the research objective. The results highlight the problems related to the flow modulation-MS combination. Specifically, it was found that sensitivity was on average three to four times higher in unmodulated and optimized single-column applications. [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]

Predicting the amount of time that a petroleum mixture has been exposed to weathering effects has applications in areas of environmental and other forensic investigations, such as aiding in determining the cause and intent of a fire. Historically, research on the evaporation rates of hydrocarbon mixtures has focused on forensic oil spill identification and predicting if a fresh sample could be weathered to give an observed composition in an aged sample. Relatively little attention has focused on approaching the problem from the other direction: estimating exposure time based on the observed composition of a weathered sample at a given time and assuming a prior composition. Here, we build upon our previous research into the weathering of model mixtures by extending our work to gasoline. Samples of gasoline with varying octane ratings and from several vendors were weathered under controlled conditions and their composition monitored over time by two-dimensional gas chromatography (GC × GC). A variety of chemometric models were explored, including partial least squares (PLS), nonlinear PLS (PolyPLS) and locally weighted regression (LWR). A hierarchical application of multivariate techniques was able to predict the time for which a sample had been exposed to evaporative weathering. Partial least squares discriminant analysis could predict whether a sample was relatively fresh (<12 h exposure time) or highly weathered (>20 h exposure time). Subsequent regression models for these classes were evaluated for accuracy using the root mean square error of prediction. LWR was the most successful, whereby fresh and highly weathered samples were predicted to within 30 min and 5 h of exposure, respectively. [ABSTRACT FROM AUTHOR]

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]

An experimental study of flame blowoff phenomenon in a bluff body stabilized flame confined in a cylindrical duct is presented. Blowoff equivalence ratios were determined for two approach velocities and three different upstream equivalence ratio profiles (uniform, inner, and outer fuel enrichment) in the absence and presence of imposed upstream velocity oscillations. The results were compared with those for the unconfined flame configuration as well. It is found that the blowoff equivalence ratios exhibit somewhat different trends for different approach velocities. For the uniform mixture profile, blowoff equivalence ratio first increases with increasing excitation frequency and then decreases at higher frequencies for the approach velocity of 5 m/s. For the 11 m/s approach velocity, the trend is different, and the blowoff equivalence ratio continuously increases with increasing excitation frequency. The blowoff equivalence ratios are higher for the confined flame configuration. An empirical correlation of the blowoff data for the uniform mixture profile is presented in terms of Damkohler, Reynolds, and Strouhal numbers. Finally, analysis of the CH* chemiluminescence signal as blowoff condition is approached shows emergence of low-frequency oscillations that are connected with intermittency of the localized flame weakening and/or extinction near the flame stabilization region. [ABSTRACT FROM AUTHOR]

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]

In standard critical care practice, cuff sphygmomanometry is widely used for intermittent blood pressure (BP) measurements. However, cuff devices offer ample possibility of modulating blood flow and pulse propagation along the artery. We explore underutilized arrangements of sensors involving cuff devices which could be of use in critical care to reveal additional information on compensatory mechanisms. In our previous work, we analyzed the response of the vasculature to occlusion perturbations by means of observations obtained non-invasively. In this study, our aim is to (1) acquire additional insights by means of invasive measurements and (2) based on these insights, further develop cuff-based measurement strategies. Invasive BP experimental data is collected downstream from the cuff in two patients monitored in the OR. It is found that highly dynamic processes occur in the distal arm during cuff inflation. Mean arterial pressure increases in the distal artery by 20 mmHg, leading to a decrease in pulse transit time by 20 ms. Previous characterizations neglected such distal vasculature effects. A model is developed to reproduce the observed behaviors and to provide a possible explanation of the factors that influence the distal arm mechanisms. We apply the new findings to further develop measurement strategies aimed at acquiring information on pulse arrival time vs. BP calibration, artery compliance, peripheral resistance, artery-vein interaction. [ABSTRACT FROM AUTHOR]

The reliability of cardiac output estimation by thermodilution during artificial ventilation was studied in anesthetized pigs at the right side of the heart. The estimates exhibited a cyclic modulation related to the ventilation. The amplitude of the modulation was independent of the level of positive end-expiratory pressure, ventilatory pattern and volemic loading of the animals. However, a non-constant phase relation existed between the ventilatory cycle and the modulation. Single observations at a fixed moment in the ventilatory cycle are therefore not appropriate for estimation of mean cardiac output nor for studying its relative changes. The averaging of estimates spread equally over the ventilatory cycle led to a much larger reduction in the deviation of the averages from the mean cardiac output than an averaging procedure of randomly selected estimates. The accuracy of estimation of mean cardiac output by two estimates equally spread in the ventilatory cycle was equal to the accuracy obtained by averaging five randomly selected estimates. Averaging four estimates, equally spread in the cycle, appeared to be the optimal procedure. For 89% of all averages an accuracy of 5% around the mean was obtained and for 99% an accuracy of +/- 10%. [ABSTRACT FROM AUTHOR]

• 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]