Set Of Columns Research Articles

Quantification of trace fatty acid methyl esters in diesel fuel by using multidimensional gas chromatography with electron and chemical ionization mass spectrometry.

Measurement of contamination of marine and naval diesel fuels (arising from product mixing or adulteration) with biodiesel or fatty acid methyl esters can be problematic, especially at very low levels. A suitable solution for this task for trace amounts of individual fatty acid methyl esters with resolution and quantification can be achieved by using a multidimensional gas chromatographic approach with electron and chemical ionization mass spectrometric detection. A unique column set comprising a 100 m methyl-siloxane nonpolar first dimension column and high-temperature ionic liquid column in the second dimension enabled identification of individual fatty acid methyl esters at below the lowest concentrations required to be reported in a diesel fuel matrix. Detection limits for individual fatty acid methyl esters compounds ranged from 0.5 to 5.0 mg/L, with excellent linearity up to 5000 mg/L and repeatability of the method from 1.3 to 3.2%. The method was applied to the analysis of diesel fuel samples with suspected biodiesel contamination. Contamination at 568 mg/L was calculated for an unknown sample and interpretation of the results permitted the determination of a likely source of the contamination.

Acoustic responses of the composite sandwich plates with lattice truss core to the subsonic turbulent boundary layer

Acoustic responses of composite sandwich plates with lattice truss core to the subsonic turbulent boundary layer are investigated. The lattice truss core is composed of four sets of orthogonal stiffeners, two sets of oblique rods and one set of vertical columns, which establishes a significant transfer path of the reactive loadings. Bending and axial motion of the vertical columns makes a great impact on the power spectral density (PSD) of the transverse displacements for the sandwich plates with lattice truss core. The convective region of the high subsonic turbulent boundary layer pressure fluctuation spectra is the predominant vibrational source in the wide frequency bands, which makes the skin plate effectively radiate sound power into the mean air flow and the trim plate transmit sound waves into the static air by wavenumber conversion. Radiated acoustic power of skin plate is much larger than transmitted sound power of the trim plate and the sandwich plates can attenuate wave propagation of the airflow turbulent wall-pressure. The principal energy of the turbulent boundary layer wall-pressure for the water flow with a low speed can be transformed into the vibrational and acoustic energy of the sandwich plates in the low frequency band, to great extent.

LAKE 2.0: a model for temperature, methane, carbon dioxide and oxygen dynamics in lakes

Abstract. A one-dimensional (1-D) model for an enclosed basin (lake) is presented, which reproduces temperature, horizontal velocities, oxygen, carbon dioxide and methane in the basin. All prognostic variables are treated in a unified manner via a generic 1-D transport equation for horizontally averaged property. A water body interacts with underlying sediments. These sediments are represented by a set of vertical columns with heat, moisture and CH4 transport inside. The model is validated vs. a comprehensive observational data set gathered at Kuivajärvi Lake (southern Finland), demonstrating a fair agreement. The value of a key calibration constant, regulating the magnitude of methane production in sediments, corresponded well to that obtained from another two lakes. We demonstrated via surface seiche parameterization that the near-bottom turbulence induced by surface seiches is likely to significantly affect CH4 accumulation there. Furthermore, our results suggest that a gas transfer through thermocline under intense internal seiche motions is a bottleneck in quantifying greenhouse gas dynamics in dimictic lakes, which calls for further research.

A New Approach for the Characterization of Organic Residues from Stone Tools Using GC×GC-TOFMS

Headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS) have traditionally been used, in combination with other analyses, for the chemical characterization of organic residues recovered from archaeological specimens. Recently in many life science fields, comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS) has provided numerous benefits over GC-MS. This study represents the first use of HS-SPME-GC×GC-TOFMS to characterize specimens from an experimental modern reference collection. Solvent extractions and direct analyses were performed on materials such as ivory, bone, antlers, animal tissue, human tissue, sediment, and resin. Thicker film column sets were preferred due to reduced column overloading. The samples analyzed by HS-SPME directly on a specimen appeared to give unique signatures and generally produced a higher response than for the solvent-extracted residues. A non-destructive screening approach of specimens may, therefore, be possible. Resin and beeswax mixtures prepared by heating for different lengths of time appeared to provide distinctly different volatile signatures, suggesting that GC×GC-TOFMS may be capable of differentiating alterations to resin in future studies. Further development of GC×GC-TOFMS methods for archaeological applications will provide a valuable tool to uncover significant information on prehistoric technological changes and cultural behavior.

Batch pervaporative fermentation with coupled membrane and its influence on energy consumption in permeate recovery and distillation stage

In the ethanol production process from sugarcane molasses, the distillation process is a high-energy demand stage. The distillation energy efficiency is strongly associated with the alcoholic fermentation performance in the process. The final ethanol concentration in the alcoholic wines has a direct impact on consumption of thermal energy in ethanol separation. In this paper, ethanol production with a H-SBMF (Hybrid-Simple Batch Membrane Fermenter) using PDMS (polydimethylsiloxane) pervaporation membrane was modelled and simulated, in order to determine its influence on energy consumption in distillation. Steam in distillation and electrical energy needs in permeate recovery were mainly influenced by membrane adaptation. The H-SBMF achieved a higher ethanol production in the range of 10–13% compared to the conventional batch fermenter, and an increase in productivity of 150%. The distillation system consisted of two sets of columns: the ethanol recovery column and the rectification column. The permeate recovery system (i.e. vacuum and compression) was regarded in order to evaluate the electrical energy requirement, and the thermal energy demand was evaluated. A decrease in steam consumption was evidenced by the adaptation of the membrane to the fermenter. Higher energy efficiencies were achieved in distillation with larger membrane areas, achieving almost 17% steam reduction.

Motion of a wheel on snow

A model of a snow layer represented by a continuous set of columns whose deformations are described by the nonlinear model of an ideal elastoplastic continuous medium with viscous properties is proposed. Under the action of a rigid wheel on snow, the field of shear stresses is specified by the law of dry friction. Prom the equations of motion describing the plane-parallel motion of the wheel, there are determined a zone of contact of the wheel with snow, the steady motions of the wheel, and a mode of slipping the wheel. The numerical results are given in tables and figures. These results are obtained by solving the nonlinear equations of motion containing definite integrals with variable integration limits.

Continuum in MDGC Technology: From Classical Multidimensional to Comprehensive Two-Dimensional Gas Chromatography.

Recent advances in multidimensional gas chromatography (MDGC) comprise methods such as multiple heart-cut (H/C) analysis and comprehensive two-dimensional gas chromatography (GC × GC); however, clear approaches to evaluate the MDGC results, choice of the most appropriate method, and optimized separation remain of concern. In order to track the capability of these analytical techniques and select an effective experimental approach, a fundamental approach was developed utilizing a time summation model incorporating temperature-dependent linear solvation energy relationship (LSER). The approach allows prediction of optimized analyte distribution in the 2D space for various MDGC approaches employing different experimental variables such as column lengths, temperature programs, and stationary phase combinations in order to evaluate separation performance (apparent (1)D, (2)D, total number of separated peaks, and orthogonality) for simulated MDGC results. The methodology applied LSER to generate results for nonpolar-polar and polar-nonpolar 2D column configurations for separation of 678 compounds in an oxidized kerosene-based jet fuel sample. Three-dimensional plots were generated in order to illustrate the dependency of separation performance on (2)D column length and number of injections for different stationary phase combinations. With a given limit of analysis time, a MDGC approach to obtain an optimized total separated peak number for a particular column set was proposed depending on (1)D and (2)D analyte peak distribution. This study introduces fundamental concepts and establishes approaches to design effective GC × GC or multiple H/C systems for different column combinations, to provide the best overall separation outcomes with the highest separated peak number and/or orthogonality.

Scalable Completion of Nonnegative Matrix with Separable Structure

Matrix completion is to recover missing/unobserved values of a data matrix from very limited observations. Due to widely potential applications, it has received growing interests in fields from machine learning, data mining, to collaborative filtering and computer vision. To ensure the successful recovery of missing values, most existing matrix completion algorithms utilise the low-rank assumption, i.e., the fully observed data matrix has a low rank, or equivalently the columns of the matrix can be linearly represented by a few numbers of basis vectors. Although such low-rank assumption applies generally in practice, real-world data can process much richer structural information. In this paper, we present a new model for matrix completion, motivated by the separability assumption of nonnegative matrices from the recent literature of matrix factorisations: there exists a set of columns of the matrix such that the resting columns can be represented by their convex combinations. Given the separability property, which holds reasonably for many applications, our model provides a more accurate matrix completion than the low-rank based algorithms. Further, we derives a scalable algorithm to solve our matrix completion model, which utilises a randomised method to select the basis columns under the separability assumption and a coordinate gradient based method to automatically deal with the structural constraints in optimisation. Compared to the state-of-the-art algorithms, the proposed matrix completion model achieves competitive results on both synthetic and real datasets.

Group-type characterization of crude oil and bitumen. Part I: Enhanced separation and quantification of saturates, aromatics, resins and asphaltenes (SARA)

Compositional analysis of crude oils is very important along the entire value chain of the oil industry, from upstream to midstream and downstream operations. An essential step of this analysis is to separate crude oil into fractions of saturate hydrocarbon (saturates), aromatic hydrocarbon (aromatics), resins, and asphaltenes (SARA). Though a number of methods have been developed for SARA separation, traditional methods involve significant drawbacks that include, but are not limited to, inconsistent results among labs and methods, extensive cross-contamination, and poor analytical precision. Here, we report on a novel automated multi-dimensional high performance liquid chromatography (AMD-HPLC) approach to enhance group-type characterization of crude oil or bitumen. The AMD-HPLC system is fully automated and developed based on a combination of adsorption and partition chromatography. It is equipped with a cyano column and a silica column. Each set of SARA columns is connected in series via multi-position valves that allow a given column to be inserted “in” or to be bypassed “out” of the flow path of the mobile phase at pre-set times in the process. In practice, a bitumen or oil sample of 0.02g is dissolved in a solvent mixture of 15% methanol, 15% acetone, and 70% chloroform, and injected into the instrument. The sample is fractionated into the four groups by selective retention through interactions with the solvent mobile phases and the column substrates. The instrument then resets and is ready to start the next run. The entire analysis cycle requires about 60min per run, including system re-conditioning. Based on its wide application at our laboratory, the AMD-HPLC is characterized by high efficiency, elimination of cross-contamination, and high reproducibility – when compared to traditional methods.

Effect of Biofouling on the Performance of Amidoxime-Based Polymeric Uranium Adsorbents

The Marine Science Laboratory at the Pacific Northwest National Laboratory evaluated the impact of biofouling on the performance or uranium adsorbents. A surface-modified polyethylene adsorbent fiber provided by Oak Ridge National Laboratory, AF adsorbent, was tested in either the presence or absence of light to simulate deployment in shallow or deep marine environments. Samples of the adsorbent fiber were exposed to seawater as loose fibers packed with glass beads in columns and as >10-cm-long braids of fiber placed in a flume that provided a continuous flow representative of natural ocean currents. Exposure tests (42 days) in column and flume settings showed that biofouling resulted in decreased uranium uptake by the adsorbent fiber. Uranium uptake was reduced by up to 30%, in the presence of simulated sunlight, which also increased biomass accumulation and altered the microbial community composition on the fibers. These results suggest that deployment below the photic zone would mitigate the effects of...

In Silico Modeling of Hundred Thousand Experiments for Effective Selection of Ionic Liquid Phase Combinations in Comprehensive Two-Dimensional Gas Chromatography.

The selection of the best column sets is one of the most tedious processes in comprehensive two-dimensional gas chromatography (GC × GC) where a multitude of choices of column sets could be employed for an individual sample analysis. We demonstrate analyte/stationary phase dependent selection approaches based on the linear solvation energy relationship (LSER), which is a reliable concept for the study of interaction mechanisms and retention prediction with a large database pool of columns and compounds. Good correlations between our predicted results, with experimental results reported in the literature, were obtained. The developed approaches were applied to the simulation of 157 920 individual experiments in GC × GC, focusing on the application of 30 nonionic liquid and 111 ionic liquid (IL) stationary phases for separation of some example sets of model compounds present in practical samples. The best column sets for each sample separation could then be extracted according to maximizing orthogonality, which estimates the quality of separation.

Larger voids in mechanically stable, loose packings of 1.3 μm frictional, cohesive particles: Their reconstruction, statistical analysis, and impact on separation efficiency

Lateral transcolumn heterogeneities and the presence of larger voids in a packing (comparable to the particle size) can limit the preparation of efficient chromatographic columns. Optimizing and understanding the packing process provides keys to better packing structures and column performance. Here, we investigate the slurry-packing process for a set of capillary columns packed with C18-modified, 1.3μm bridged-ethyl hybrid porous silica particles. The slurry concentration used for packing 75μm i.d. fused-silica capillaries was increased gradually from 5 to 50mg/mL. An intermediate concentration (20mg/mL) resulted in the best separation efficiency. Three capillaries from the set representing low, intermediate, and high slurry concentrations were further used for three-dimensional bed reconstruction by confocal laser scanning microscopy and morphological analysis of the bed structure. Previous studies suggest increased slurry concentrations will result in higher column efficiency due to the suppression of transcolumn bed heterogeneities, but only up to a critical concentration. Too concentrated slurries favour the formation of larger packing voids (reaching the size of the average particle diameter). Especially large voids, which can accommodate particles from>90% of the particle size distribution, are responsible for a decrease in column efficiency at high slurry concentrations. Our work illuminates the increasing difficulty of achieving high bed densities with small, frictional, cohesive particles. As particle size decreases interparticle forces become increasingly important and hinder the ease of particle sliding during column packing. While an optimal slurry concentration is identified with respect to bed morphology and separation efficiency under conditions in this work, our results suggest adjustments of this concentration are required with regard to particle size, surface roughness, column dimensions, slurry liquid, and external effects utilized during the packing process (pressure protocol, ultrasound, electric fields).

Group-type characterization of crude oil and bitumen. Part II: Efficient separation and quantification of normal-paraffins iso-paraffins and naphthenes (PIN)

The SARA (saturates, aromatics, resins, and asphaltenes) separation and quantification have been widely used for characterizing the composition of crude oil and bitumen. The saturate hydrocarbons are the most valuable fraction of the oil industry and contain vital geochemical information for determining the origin and formation of petroleum fluids and for assessing the hydrocarbon potential and sedimentary environment of source rocks. It is therefore necessary to further separate the saturate fraction into normal paraffins, iso-paraffins and naphthenes (PIN fractions). Nevertheless, the convenient approach of PIN separation has never been reported on in the literature. Here, we present an efficient method that allows us to further separate the saturate fraction of crude oil or bitumen into PIN fractions through the automated multi-dimensional high performance liquid chromatography system (AMD-HPLC). In essence, the system is equipped with a “PIN1” column (Silicon: S115) packed with a 5.4Å molecular sieve and a “PIN2” column (Silicon: 50%S115+50%S130) packed with a 6.2Å molecular sieve. Each set of columns is connected in a series via multi-position valves that allow a given column to be inserted “in” or to be by-passed “out” of the flow path of the mobile phase at pre-set times in the process. When use iso-octane and n-octane or their mixture as mobile phases, the system separates the saturate hydrocarbon into PIN fractions simply through three steps under a temperature range of 25–140°C. An entire PIN analysis cycle takes nearly 60min, including system re-conditioning. The separated PIN fractions can be quantified using either gravimetric method or evaporative light scattering detector (ELSD) technique. Experimental results exhibit excellent qualitative and quantitative capability.

Construction of the minimal dominating set in the design of Wi-Fi-network

Currently, wireless technology is becoming the preferred, and in some cases the only possible for the information communication devices. If you need coverage of a large space with a complex configuration arises the need to efficiently host multiple Wi-Fi emitters, providing a stable connection with each possible location of the receiver signals. Suppose we have a model that allows to determine the coverage of a stable connection Wi-Fi emitter at a given spatial point. Then the problem of locating Wi-Fi emitters can be formulated as determining a discrete set of locations of transducers satisfying the condition. Otherwise, it is necessary to determine the positions of all the emitters that completely cover a given area, and the number of emitters should be minimal. In this formulation it is the task of the lowest coverage – the problem of finding the smallest set of columns of the matrix, "covering" all of her lines. To develop methods for solving a problem of the smallest covering usually resort to its matrix interpretation, which reduces to the problem of the smallest dominating set of a graph. From the point of view of the formulation of the problem of the smallest covering two cases are possible configuration of the coverage area of the surrounding space Wi-Fi emitters: 1. without variable. Its peculiarity is that the coverage area is completely defined by the location of the emitter. It is possible in the case where the coverage area of the symmetric or the orientation of the directivity diagram of the radiation is fixed. In this case it is possible to build a graph associated with the set of locations of emitters in which each point of placement are associated with adjacent vertices. In this formulation we arrive at the problem of the smallest dominating set of a graph. 2. Variable. It takes place in the case when the diagram of radiation is directed, and the coverage area may vary depending on the orientation of the emitter. That is, the actual emitter can be deployed in an infinite number of different provisions, but the limb covered points significantly limits the number of different orientations. In this case, each point position of the transmitter can be put into correspondence with several matrix rows and cover each point will correspond to exactly one column.

Conventional and enantioselective gas chromatography with microfabricated planar columns for analysis of real-world samples of plant volatile fraction

Within a project exploring the application of lab-on-chip GC to in-field analysis of the plant volatile fraction, this study evaluated the performance of a set of planar columns (also known as microchannels, MEMS columns, or microfabricated columns) of different dimensions installed in a conventional GC unit. Circular double-spiral-shaped-channel planar columns with different square/rectangular sections up to 2m long were applied to the analysis of both essential oils and headspace samples of a group of medicinal and aromatic plants (chamomile, peppermint, sage, rosemary, lavender and bergamot) and of standard mixtures of related compounds; the results were compared to those obtained with reference narrow-bore columns (l:5m, dc:0.1mm, df:0.1μm). The above essential oils and headspaces were first analyzed quali-and quantitatively with planar columns statically coated with conventional stationary phases (5%-phenyl-polymethylsiloxane and auto-bondable nitroterephthalic-acid-modified polyethylene glycol), and then submitted to chiral recognition of their diagnostic markers, by enantioselective GC with a planar columns coated with a cyclodextrin derivative (30% 6I–VII-O-TBDMS-3I–VII-O-ethyl-2I–VII-O-ethyl-β-cyclodextrin in PS-086). Column characteristics and analysis conditions were first optimized to obtain suitable retention and efficiency for the samples investigated. The planar columns tested showed performances close to the reference conventional narrow-bore columns, with theoretical plate numbers per meter (N/m) ranging from 6100 to 7200 for those coated with the conventional stationary phases, and above 5600 for those with the chiral selector.

Constraining the oceanic barium cycle with stable barium isotopes

The distribution of barium (Ba) concentrations in seawater resembles that of nutrients and Ba has been widely used as a proxy of paleoproductivity. However, the exact mechanisms controlling the nutrient-like behavior, and thus the fundamentals of Ba chemistry in the ocean, have not been fully resolved. Here we present a set of full water column dissolved Ba (DBa) isotope (δ137BaDBa) profiles from the South China Sea and the East China Sea that receives large freshwater inputs from the Changjiang (Yangtze River). We find pronounced and systematic horizontal and depth dependent δ137BaDBa gradients. Beyond the river influence characterized by generally light signatures (0.0 to +0.3‰), the δ137BaDBa values in the upper water column are significantly higher (+0.9‰) than those in the deep waters (+0.5‰). Moreover, δ137BaDBa signatures are essentially constant in the entire upper 100 m, in which dissolved silicon isotopes are fractionated during diatom growth resulting in the heaviest isotopic compositions in the very surface waters. Combined with the decoupling of DBa concentrations and δ137BaDBa from the concentrations of nitrate and phosphate this implies that the apparent nutrient-like fractionation of Ba isotopes in seawater is primarily induced by preferential adsorption of the lighter isotopes onto biogenic particles rather than by biological utilization. The subsurface δ137BaDBa distribution is dominated by water mass mixing. The application of stable Ba isotopes as a proxy for nutrient cycling should therefore be considered with caution and both biological and physical processes need to be considered. Clearly, however, Ba isotopes show great potential as a new tracer for land–sea interactions and ocean mixing processes.

Direct Measurement of Trace Elemental Mercury in Hydrocarbon Matrices by Gas Chromatography with Ultraviolet Photometric Detection.

We introduce a technique for the direct measurement of elemental mercury in light hydrocarbons such as natural gas. We determined elemental mercury at the parts-per-trillion level with high precision [<3% RSD (n = 20 manual injection)] using gas chromatography with ultraviolet photometric detection (GC-UV) at 254 nm. Our approach requires a small sample volume (1 mL) and does not rely on any form of sample preconcentration. The GC-UV separation employs an inert divinylbenzene porous layer open tubular column set to separate mercury from other components in the sample matrix. We incorporated a 10-port gas-sampling valve in the GC-UV system, which enables automated sampling, as well as back flushing capability to enhance system cleanliness and sample throughput. Total analysis time is <2 min, and the procedure is linear over a range of 2-83 μg/m(3) [correlation coefficient of R(2) = 0.998] with a measured recovery of >98% over this range.

Strengthening under Load: Experimental and Numerical Research

The paper presents experimental and numerical research of strengthening of columns under load using welded plates. Three sets of three columns each were tested. All columns were 3 m long. The load from loading cylinders was transmitted through knife-edge bearings, which ensured pinned boundary condition perpendicular to the weaker axis. Set (A) comprised columns with welded T shaped cross-section. Set (B) comprised columns with welded monosymmetric I shaped cross-section. Both sets (A) and (B) had been loaded monotonically until collapse occurred. Set (C) contained columns with T shaped cross-section with the same dimensions as the columns in set (A). The columns from set (C) were first loaded to 70 kN. The force was being held constant and the second flange was being welded to the web under load. After the welding process was finished and the specimen cooled, the column was loaded to failure. The average forces at collapse of column sets (A), (B) and (C) were 143 kN, 308 kN and 323 kN, respectively. It was unexpected that the columns strengthened under load (C) had higher average resistance than the columns welded without preload (B). It could be caused by the residual stress and distortion caused by welding. The study includes the results of finite element models of the problem created in ANSYS software. The results from the experiments and numerical simulations were compared.

A theoretical investigation of the diatom cell size reduction–restitution cycle

An individual based model for the life cycle of diatoms (DiaLCM) has been developed to investigate the combined effects of the cell cycle and the cell size reduction–restitution cycle (SRRC) of this important marine phytoplankton group. Growth, grazing mortality and sinking are considered as size-dependent processes. The model is tested against laboratory results and reproduces the typical saw tooth pattern of mean population size as the result of the SRRC. The development of cell-size distribution patterns, their dependence on the environment and their influence on the ecosystem is investigated in a one-dimensional water column setting, where the diatoms face competition by a bulk phytoplankton species. Using a perpetual-year forcing, we find that the SRRC introduces interannual variability with periods of diatoms dominance interrupted by dominance of other phytoplankton. We find that inter- and intraspecific competition explains several of the observed characteristics in size frequency distributions, in particular the relatively narrow cell size spectra. In agreement with observations modeled auxosporulation events are rare with low numbers of auxospores.

Displacement phenomena in lectin affinity chromatography.

The work described here examines displacement phenomena that play a role in lectin affinity chromatography and their potential to impact reproducibility. This was achieved using Lycopersicon esculentum lectin (LEL), a lectin widely used in monitoring cancer. Four small identical LEL columns were coupled in series to form a single affinity chromatography system with the last in the series connected to an absorbance detector. The serial affinity column set (SACS) was then loaded with human plasma proteins. At the completion of loading, the column set was disassembled, the four columns were eluted individually, the captured proteins were trypsin digested, the peptides were deglycosylated with PNGase F, and the parent proteins were identified through mass spectral analyses. Significantly different sets of glycoproteins were selected by each column, some proteins appearing to be exclusively bound to the first column while others were bound further along in the series. Clearly, sample displacement chromatography (SDC) occurs. Glycoproteins were bound at different places in the column train, identifying the presence of glycoforms with different affinity on a single glycoprotein. It is not possible to see these phenomena in the single column mode of chromatography. Moreover, low abundance proteins were enriched, which facilitates detection. The great advantage of this method is that it differentiates between glycoproteins on the basis of their binding affinity. Displacement phenomena are concluded to be a significant component of the separation mechanism in heavily loaded lectin affinity chromatography columns. This further suggests that care must be exercised in sample loading of lectin columns to prevent analyte displacement with nonretained proteins.