Analyzing crude oils from the Junggar Basin(NW China) using comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry(GC×GC-TOFMS)

As a new technology of analyzing crude oils, comprehensive two-dimensional gas chromatography cou- pled with time-of-flight mass spectrometry （GCxGC- TOFMS） has received much research attention. Here we present a case study in the Junggar Basin of NW China. Results show that the hydrocarbons, including saturates and aromatics, were all well-separated without large co- elution, which cannot be realized by conventional one-dimensional GC-MS. The GC×GC technique is especially effective for analyzing aromatics and low-to-middle- molecular-weight hydrocarbons, such as diamondoids. The geochemical characteristics of crude oils in the study area were investigated through geochemical parameters extracted by GC×GC-TOFMS, improving upon the understanding obtained by GC-MS. Thus, the work here represents a new successful application of GC×GC- TOFMS, showing its broad usefulness in petroleum geochemistry.

Effective Qubit Emerging from the Nanoheterointerface Two-Dimensional Electron Gas Photodynamics

An “Eigenstate Adjustment Autonomy” Model, permeated by the Nanosystem’s Fermi Level Pinning along with its rigid Conduction Band Discontinuity, compatible with pertinent Experimental Measurements, is being employed for studying how the Functional Eigenstate of the Two-Dimensional Electron Gas (2DEG) dwelling within the Quantum Well of a typical Semiconductor Nanoheterointerface evolves versus (cryptographically) selectable consecutive Cumulative Photon Dose values. Thus, it is ultimately discussed that the experimentally observed (after a Critical Cumulative Photon Dose) Phenomenon of 2DEG Negative Differential Mobility allows for the Nanosystem to exhibit an Effective Qubit Specific Functionality potentially conducive to (Telecommunication) Quantum Information Registering.

Identification of petroleum aromatic fraction by comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry

Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry(GC×GC-TOFMS) is commercially available in the 1990s,with the characteristics of large peak capacity,high resolution,high sensitivity,etc.However,its application to the petroleum and geological analyses is just emerging in China and overseas.In this research,the analytical method for petroleum aromatic fraction using GC×GC-TOFMS is set up,via the choice of the column system and optimization of setting parameters,such as temperature programming,modulation time,hot pulse time,flow rate of carrier gas,data acquisition rate and data processing.The results indicate that different polar compounds of aromatic fraction distribute as bands on structured GC×GC chromatogram.Within each band,homologous compounds appear as a roof-tile structure based on the number of substituent residues.The aromatic compounds are identified and characterized according to the GC×GC chromatogram and mass spectra.According to the polarity and the number of rings,aromatic compounds are spatially present on one chromatogram,which directly reflects the distribution characteristics of complex compounds of aromatic hydrocarbons.In addition,quantitative analysis is favored as some overlapped peaks on traditional GC-MS chromatogram have been separated completely on GC×GC.Some heterocyclic atom aromatic compounds at trace level can be clearly identified using this method,for polarity differences from other interfered aromatic compounds.The development of this method and chromatogram recognition offer petroleum geologists a practical example for the application performance of GC×GC-TOFMS.

Comparison of geochemical parameters derived from comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry and conventional gas chromatography-mass spectrometry

The saturated and aromatic hydrocarbon fractions of crude oil samples have been analyzed by using comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry （GCxGC-TOFMS） and conventional gas chro- matography-mass spectrometry （GC-MS）. In order to investigate the consistency and discrepancy of the obtained data from the two instruments, some petroleum geochemical parameters have been compared. A comparison of 23 geochemical parameters indicates that 10 parameters are comparable from the two instruments with less than 5% deviations. Therefore, GCxGC-TOFMS is equivalent to conventional GC-MS in some geochemical parameter acquisitions. However, the other 13 parameters are discrepant, including gammacerane / αβ-hopane, Ts/Tm, 2-ethyl-naphthalene / 1-ethyl-naphthalene （ENR）, （2, 6-dimethyl-naphthalene ＋2,7-dimethyl-naphthalene） / 1,5-dimethyl-naphthalene （DNR）, etc. Furthermore, compared to GCxGC-TOFMS, some low concentration compounds could not be detected by the conventional GC-MS, which results in the missing of related geochemical data. Normally, this is caused by the limited separation power and peak capacity of the conventional GC column. Besides, the co-eluting peak integrations are also affected significantly due to the incomplete separation of the compounds. Some low concentration compounds might not be detected because of the interference from the baseline noise or from other substances. GCxGC-TOFMS prevails in compound separation against the conventional GC-MS by avoiding co-elution, which achieves more accurate and precise peak area measurement with the presence of a true baseline. So petroleum geochemical parameters obtained from the GCxGC-TOFMS GCxGC-TOFMS may become one of the most effective analytical are more reliable than those from the conventional GC-MS tools for the oil and gas geochemical study.

Qualitative Analysis of A Sulfur-fumigated Chinese Herbal Medicine by Comprehensive Two-Dimensional Gas Chromatography and High-Resolution Time of Flight MassSpectrometry Using Colorized Fuzzy Difference Data Processing

To investigate the chemical transformation of volatile compounds in sulfur-fumigated Radix Angelicae Sinensis. A comprehensive two-dimensional gas chromatography (GCxGC) and high-resolution time-of-flight mass spectrometry (HR-TOF/MS) with colorized fuzzy difference (CFD) method was used to investigate the effect of sulfur-fumigation on the volatile components from Radix Angelicae Sinensis. Twenty-five compounds that were found in sun-dried samples disappeared in sulfur-fumigated samples. Seventeen volatile components including two sulfur-containing compounds were newly generated for the first time in volatile oils of sulfur-fumigated Radix Angelicae Sinensis. The strategy can be successfully applied to rapidly and holistically discriminate sun-dried and sulfur-fumigated Radix Angelicae Sinensis. GCxGC-HR-TOF/MS based CFD is a powerful and feasible approach for the global quality evaluation of Radix Angelicae Sinensis as well as other herbal medicines.

Gas Chromatographic Method for Identification and Quantification of Commonly Used Residual Solvents in Pharmaceuticals Products

Background: Impurities are not expected in the final pharmaceutical products. All impurities should be regulated in both drug substances and drug products in accordance with pharmacopeias and ICH guidelines. Three different types of impurities are generally available in the pharmaceutical’s product specification: organic impurities, inorganic impurities, and residual solvents. Residual solvents are organic volatile chemicals used or generated during the manufacturing of drug substances or drug products. Purpose: The aim of this study is to develop a cost-effective gas chromatographic method for the identification and quantification of some commonly used solvents—methanol, acetone, isopropyl alcohol (IPA), methylene chloride, ethyl acetate, tetrahydrofuran (THF), benzene, toluene, and pyridine—in pharmaceutical product manufacturing. This method will be able to identify and quantify the multiple solvents within a single gas chromatographic procedure. Method: A gas chromatography (GC) equipped with a headspace sampler and a flame ionization detector, and a column DB 624, 30-meter-long × 0.32-millimeter internal diameter, 1,8 μm-thick, Brand-Agilent was used to develop this method. The initial GC oven temperature was 40°C and held for 5 minutes. It was then increase to 80˚C at a rate of 2˚C per minute, followed by a further increase to 225˚C at a rate of 30˚C per minute, with a final hold at 225˚C for 10 minutes. Nitrogen was used as a carrier gas at a flow rate of 1.20 mL per minute. Dimethyl sulfoxide (DMSO) was selected as sample solvent. Results: The developed method is precise and specific. The percent RSD for the areas of six replicate injections of this gas chromatographic method was within 10.0 and the recovery result found within 80.0% to 120.0%.

Determination of 14 Organophosphorus Pesticide Residues in Mutton by Gel Permeation Chromatography-Gas Chromatography-Mass Spectrometry(GPC-GC-MS)

[Objectives]This study was conducted to purify mutton samples by gel permeation chromatography(GPC).[Methods]Fourteen organophosphorus pesticide residues in samples were qualitatively and quantitatively analyzed by gas chromatography-mass spectrometry(GC-MS)in selective ion scanning mode(SIM).[Results]The organophosphorus pesticide standard solutions showed good linearity in the mass concentration range of 0.1-10.0μg/ml with correlation coefficients(r)not lower than 0.999,and the detection limits(S=3 N)ranged from 0.01 to 0.05 mg/kg.The average recovery values were in the range of 80.2%-99.7%,with relative standard deviations(RSDs,n=3)in the range of 1.8%-6.3%,at the addition levels of 0.5,1.0 and 2.0 mg/kg.[Conclusions]The method is simple,sensitive and accurate,and can be used for the determination of organophosphorus pesticide residues in mutton.

Un raveling the acetals as ageing markers of Chinese Highland Qingke Baijiu using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry combined with metabolomics approach

Objectives:The ageing process has a significant impact on the aroma of Chinese Baijiu,which could strengthen the desirable flavor characteristics and reduce the undesirable ones.The aim of this study was to observe the in itiation of mean in gful cha nges in volatile fracti on and locate the ageing markers during ageing storage of Chinese Highland Qingke Baijiu.Materials and Methods:Samples of Chinese Qingke Baijiu were aged for 0,1,2,3,4,5,6,7,8,9,10,and 11 mon ths before an alysis.The samples were isolated by liquid-liquid extraction and then analyzed by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry.The acquired data were processed by untargeted and targeted metabolomics approach to locate the ageing markers.Results:The untargeted metabolomics analysis(hierarchical clustering analysis,HCA)shows that the chemical composition of Qingke Baijiu presents a statistically sigrdficant deviation from the reference scenario after 5 mon ths.Subsequently,supervised statistics analysis(orthogo nal partial least squares discrimination analysis)was performed to locate the markers,which changed sigrdficantly during ageing.Fifteen markers were located,and seven of them were acetals.Notably,1,1-diethoxy-propane,1,1-diethoxy-butane,and 1,1-diethoxy-3-methyl-butane are important contributors to the flavor of Chinese Baijiu.The identified markers were applied for the untargeted metabolomics(HCA),and the results revealed that these markers could divide the Qingke Baijiu into two ageing stages,0-5 months and 6-11 months.Conclusion:The results suggest that it is a valuable tool for monitoring the changes of volatile compounds and locating the age markers in Chinese Baijiu.

Influence of Al Composition on Transport Properties of Two-Dimensional Electron Gas in Al_xGa_(1-x)N/GaN Heterostructures

Magnetotransport properties of two-dimensional electron gases （2DEG） in AlxGa1-x N/GaN heterostructures with different Al compositions are investigated by magnetotransport measurements at low temperatures and in high magnetic fields. It is found that heterostructures with a lower Al composition in the barrier have lower 2DEG concentration and higher 2DEG mobility.

Offline two-dimensional liquid chromatography coupled with ion mobility-quadrupole time-of-flight mass spectrometry enabling fourdimensional separation and characterization of the multicomponents from white ginseng and red ginseng

Inherent complexity of plant metabolites necessitates the use of multi-dimensional information to accomplish comprehensive profiling and confirmative identification.A dimension-enhanced strategy,by offline two-dimensional liquid chromatography/ion mobility-quadrupole time-of-flight mass spectrometry(2 D-LC/IM-QTOF-MS)enabling four-dimensional separations(2 D-LC,IM,and MS),is proposed.In combination with in-house database-driven automated peak annotation,this strategy was utilized to characterize ginsenosides simultaneously from white ginseng(WG)and red ginseng(RG).An offline 2 DLC system configuring an Xbridge Amide column and an HSS T3 column showed orthogonality 0.76 in the resolution of ginsenosides.Ginsenoside analysis was performed by data-independent high-definition MSE(HDMSE)in the negative ESI mode on a Vion?IMS-QTOF hybrid high-resolution mass spectrometer,which could better resolve ginsenosides than MSEand directly give the CCS information.An in-house ginsenoside database recording 504 known ginsenosides and 58 reference compounds,was established to assist the identification of ginsenosides.Streamlined workflows,by applying UNIFI?to automatedly annotate the HDMSEdata,were proposed.We could separate and characterize 323 ginsenosides(including 286 from WG and 306 from RG),and 125 thereof may have not been isolated from the Panax genus.The established 2 D-LC/IM-QTOF-HDMSEapproach could also act as a magnifier to probe differentiated components between WG and RG.Compared with conventional approaches,this dimensionenhanced strategy could better resolve coeluting herbal components and more efficiently,more reliably identify the multicomponents,which,we believe,offers more possibilities for the systematic exposure and confirmative identification of plant metabolites.

Establishing a protein expression profile database for the normal human pituitary gland using two-dimensional high-performance liquid chromatography combined with LTQ-Orbitrap mass spectrometry

In this study, we selected adult normal pituitary gland tissues from six patients during operations for pituitary microadenomas via the transsphenoidal approach for extended normal pituitary tissue resection around the tumor, and analyzed the protein expression of human normal pituitary using two-dimensional high-performance liquid chromatography combined with LTQ-Orbitrap mass spectrometry proteomics technology. The ten most highly expressed proteins in normal human pituitary were： alpha 3 type VI collagen isoform 5 precursor （abundance among tall pituitary proteins 1.30%）, fibrinogen beta chain preproprotein （0.99%）, vimentin （0.73%）, prolactin （0.69%）, ATP synthase, H~ transporting and mitochondrial F1 complex beta subunit precursor （0.52%）, keratin I （0.49%）, growth hormone （0.45%）, carbonic anhydrase I （0.40%）, heat shock protein 90 kDa I （0.31%）, and annexin V （0.30%）. Based on the biological function classifications of these proteins, the top three categories by content were neuroendocrine proteins （abundance among all pituitary proteins, 40.1%）, catalytic and metabolic proteins （28.3%）, and cell signal transduction proteins （9.8%）. Based on cell positioning classification, the top three categories were cell organelle （24.5%） membrane （20.8%）, and cytoplasm （13.0%）. Based on biological process classification, the top three categories of proteins are involved in physiological processes （42.9%）, cellular processes （40.4%）, and regulation of biological processes （9.1%）. Our experimental findings indicate that a protein expression profile database of normal human pituitary can be precisely and efficiently established by proteomics technology.

Two-dimensional electron gas characteristics of InP-based high electron mobility transistor terahertz detector

The samples of InxGa（1-x）As/In（0.52）Al（0.48）As two-dimensional electron gas（2DEG）are grown by molecular beam epitaxy（MBE）.In the sample preparation process,the In content and spacer layer thickness are changed and two kinds of methods,i.e.,contrast body doping andδ-doping are used.The samples are analyzed by the Hall measurements at 300 Kand 77 K.The InxGa1-xAs/In0.52Al0.48As 2DEG channel structures with mobilities as high as 10289 cm^2/V·s（300 K）and42040 cm^2/V·s（77 K）are obtained,and the values of carrier concentration（Nc）are 3.465×10^12/cm^2 and 2.502×10^12/cm^2,respectively.The THz response rates of In P-based high electron mobility transistor（HEMT）structures with different gate lengths at 300 K and 77 K temperatures are calculated based on the shallow water wave instability theory.The results provide a reference for the research and preparation of In P-based HEMT THz detectors.

Formation of two-dimensional electron gas at AlGaN/GaN heterostructure and the derivation of its sheet density expression

Models for calculating the sheet densities of two-dimensional electron gas （2DEG） induced by spontaneous and piezoelectric polarization in A1GaN/GaN, A1GaN/A1N/GaN, and GaN/A1GaN/GaN heterostructures are provided. The detailed derivation process of the expression of 2DEG sheet density is given. A longstanding confusion in a very widely cited formula is pointed out and its correct expression is analyzed in detail.

The low-temperature mobility of two-dimensional electron gas in AlGaN/GaN heterostructures

To reveal the internal physics of the low-temperature mobility of two-dimensional electron gas （2DEG） in Al- GaN/GaN heterostructures, we present a theoretical study of the strong dependence of 2DEG mobility on Al content and thickness of AlGaN barrier layer. The theoretical results are compared with one of the highest measured of 2DEG mobility reported for AlGaN/GaN heterostructures. The 2DEG mobility is modelled as a combined effect of the scat- tering mechanisms including acoustic deformation-potential, piezoelectric, ionized background donor, surface donor, dislocation, alloy disorder and interface roughness scattering. The analyses of the individual scattering processes show that the dominant scattering mechanisms are the alloy disorder scattering and the interface roughness scattering at low temperatures. The variation of 2DEG mobility with the barrier layer parameters results mainly from the change of 2DEG density and distribution. It is suggested that in AlGaN/GaN samples with a high Al content or a thick AlGaN layer, the interface roughness scattering may restrict the 2DEG mobility significantly, for the AlGaN/GaN interface roughness increases due to the stress accumulation in AlGaN layer.

Influence of a two-dimensional electron gas on current-voltage characteristics of Al_(0.3)Ga_(0.7) N/GaN high electron mobility transistors

The J-V characteristics of AltGa1 tN/GaN high electron mobility transistors（HEMTs） are investigated and simulated using the self-consistent solution of the Schro dinger and Poisson equations for a two-dimensional electron gas（2DEG） in a triangular potential well with the Al mole fraction t = 0.3 as an example.Using a simple analytical model,the electronic drift velocity in a 2DEG channel is obtained.It is found that the current density through the 2DEG channel is on the order of 10^13 A/m^2 within a very narrow region（about 5 nm）.For a current density of 7 × 10^13 A/m62 passing through the 2DEG channel with a 2DEG density of above 1.2 × 10^17 m^-2 under a drain voltage Vds = 1.5 V at room temperature,the barrier thickness Lb should be more than 10 nm and the gate bias must be higher than 2 V.

High-mobility two-dimensional electron gases at oxide interfaces:Origin and opportunities

Our recent experimental work on metallic and insulating interfaces controlled by interfacial redox reactions in SrTiO3-based heterostructures is reviewed along with a more general background of two-dimensional electron gas （2DEG） at oxide interfaces. Due to the presence of oxygen vacancies at the SrTiO3 surface, metallic conduction can be created at room temperature in perovskite-type interfaces when the overlayer oxide ABO3 has Al, Ti, Zr, or Hf elements at the B sites. Furthermore, relying on interface-stabilized oxygen vacancies, we have created a new type of 2DEG at the heterointerface between SrTiO3 and a spinel γ-Al2O3 epitaxial film with compatible oxygen ion sublattices. This 2DEG exhibits an electron mobility exceeding 100000 cm2·V-1·s-1, more than one order of magnitude higher than those of hitherto investigated perovskite-type interfaces. Our findings pave the way for the design of high-mobility all-oxide electronic devices and open a route toward the studies of mesoscopic physics with complex oxides.

First-principles study on improvement of two-dimensional hole gas concentration and confinement in AlN/GaN superlattices

Using first-principles calculations based on density functional theory,we have systematically studied the influence of in-plane lattice constant and thickness of slabs on the concentration and distribution of two-dimensional hole gas(2 DHG)in AlN/GaN superlattices.We show that the increase of in-plane lattice constant would increase the concentration of 2 DHG at interfaces and decrease the valence band offset,which may lead to a leak of current.Increasing the thickness of AlN and/or decreasing the thickness of GaN would remarkably strengthen the internal field in GaN layer,resulting in better confinement of 2 DHG at AlN/GaN interfaces.Therefore,a moderate larger in-plane lattice constant and thicker AlN layer could improve the concentration and confinement of 2 DHG at AlN/GaN interfaces.Our study could serve as a guide to control the properties of 2 DHG at Ⅲ-nitride interfaces and help to optimize the performance of p-type nitride-based devices.

Thermodynamic criterion for searching high mobility two-dimensional electron gas at KTaO_(3)interface

Two-dimensional electron gases(2 DEGs)formed at the interface between two oxide insulators present a promising platform for the exploration of emergent phenomena.While most of the previous works focused on SrTiO_(3-)based 2 DEGs,here we took the amorphous-ABO_(3)/KTaO_(3)system as the research object to study the relationship between the interface conductivity and the redox property of B-site metal in the amorphous film.The criterion of oxide-oxide interface redox reactions for the B-site metals,Zr,Al,Ti,Ta,and Nb in conductive interfaces was revealed:the formation heat of metal oxide,ⅢH_(f)^(o),is lower than-350 kJ/(mol O)and the work function of the metalΦis in the range of 3.75 eV<Φ<4.4 eV.Furthermore,we found that the smaller absolute value ofⅢH_(f)^(o)and the larger value ofΦof the B-site metal would result in higher mobility of the two-dimensional electron gas that formed at the corresponding amorphous-ABO_(3)/KTaO_(3)interface.This finding paves the way for the design of high-mobility all-oxide electronic devices.

The kinetic magnetoelectric effect in laterally boundary-confined ballistic two-dimensional hole gases

A theoretical investigation is presented on the characteristics of the kinetic magnetoelectric effect in laterally boundary-confined ballistic two-dimensional hole gases. It was shown that, though the momentum-dependent effective magnetic fields felt by charge carriers due to the spin-orbit interaction are in-plane orientated in such systems, both in-plane polarized and normal polarized nonequilibrium spin polarization densities could be electrically induced by the kinetic magnetoelectric effect, and the induced nonequilibrium spin polarizations exhibit some interesting characteristics. The characteristics we found indicate that there may be some possible relation between this effect and some recent experimental findings.

A comparison of the transport properties of bilayer graphene,monolayer graphene,and two-dimensional electron gas

We studied and compared the transport properties of charge carriers in bilayer graphene, monolayer graphene, and the conventional semiconductors （the two-dimensional electron gas （2DEG））. It is elucidated that the normal incidence transmission in the bilayer graphene is identical to that in the 2DEG but totally different from that in the monolayer graphene. However, resonant peaks appear in the non-normal incidence transmission profile for a high barrier in the bilayer graphene, which do not occur in the 2DEG. Furthermore, there are tunneling and forbidden regions in the transmission spectrum for each material, and the division of the two regions has been given in the work. The tunneling region covers a wide range of the incident energy for the two graphene systems, but only exists under specific conditions for the 2DEG. The counterparts of the transmission in the conductance profile are also given for the three materials, which may be used as high-performance devices based on the bilayer graphene.