全二维气相色谱-飞行时间质谱对催化裂化汽油的定性与定量分析

采用全二维气相色谱-飞行时间质谱(GC×GC-TOF MS)对催化裂化汽油全馏分进行了定性与定量分析,建立了相应的分析方法.结果表明,汽油族组成中的烷烃、烯烃、环烷烃、芳烃在全二维点阵谱图中呈分区域、带状的分布特点.GC×GC-TOF MS根据催化裂化汽油组分内分子的沸点及极性差异对其进行两个维度分离,极大地避免了普通色谱法分析过程中沸点相似化合物共流的弊端,实现催化裂化汽油组分的精确分离和准确定性分析.通过引入响应因子,修正了不同性质的烃类在电离源上电离效率的差异,使得TOF对催化裂化汽油族组成的定量结果与普通气相色谱法的定量结果的相关性较好,且应用GC×GC-TOF MS方法获得了催化裂化汽油更为精确的族组成信息.GC×GC-TOF MS为催化裂化汽油精确表征提供了一种有效方法.     

全二维气相色谱/飞行时间质谱(GC×GC/TOFMS)用于烟叶中挥发、半挥发性碱性化合物的组成研究

建立了烟叶中挥发性、半挥发性碱性化合物组成研究的全二维气相色谱/飞行时间质谱(GC×GC/TOFMS)分析方法, 并用所建立的方法对香料烟中碱性化合物进行了表征. 对比了一维气相色谱和全二维色谱方法用于烟叶碱性组分组成分析的效果. 一维色谱质谱方法共鉴定出45种碱性化合物. 用所建立的全二维气相色谱方法, 采用TOFMS谱图库检索结合全二维特有的包含结构信息的二维谱图, 通过族分离和结构谱图鉴定, 鉴定出了香料烟中挥发性、半挥发性碱性组分共92种. 包括吡咯类化合物6种, 吡啶类化合物39种, 吡嗪类化合物10种, 苯胺类化合物11种, 喹啉类化合物11种, 吲哚类4种和其他类化合物11种. 同时对不同类别的化合物在二维气相色谱上的分布模式进行了研究. 研究结果表明, 全二维色谱飞行时间质谱的高分辨率和特有的定性手段适合于烟叶这类复杂植物体系的化学组成研究.     

Projection of multidimensional GC data into alternative dimensions—exploiting sample dimensionality and structured retention patterns

Comprehensive multidimensional gas chromatography (GC×GC) is a powerful separation technique. One of the features of this technique is that it offers separations with more apparent structure than that offered by conventional one-dimensional GC (1-D GC). While some previous studies have alluded to this structure, and used structured retention patterns for some simple classifications, the topic of structured retention in GC×GC has not been studied in any great detail. Using the separation of fatty acid methyl esters (FAME) on both nonpolar/polar and polar/nonpolar column sets, the interaction between the separation dimensions and the sample dimensions is explored here. The GC×GC separation of a series of compounds is presented as a projection of the sample from sample space, a p-dimensional space with dimensions defined by the dimensionality of the sample, into separation space: for GC×GC, a two-dimensional plane passing through the sample space in an orientation defined by the separation conditions. Using this conceptual model and some a priori knowledge of the sample, it is shown how the image of the sample in the separation space can be used to construct an image of the sample in alternate dimensions, such as second dimension retention factor (²k) vs. chain length in the case of FAME. These projections into alternate dimensions should facilitate the interpretation of the complex patterns found within the GC×GC chromatogram for the identification and classification of compounds.     

气相色谱近年的发展

简要阐述了近几年气相色谱(GC)的发展和特点。GC是一个成熟的技术,广泛地应用于各个领域,近几年GC的发展除了继续研究新的固定相和高性能的毛细管色谱柱之外,主要在全二维气相色谱(GC×GC)、快速GC、便携式GC仪和微型GC仪几个方面。近几年新研究的GC固定相主要集中在常温离子液体和各种环糊精的衍生物。现在GC研究者趋向于使用商品化的GC毛细管柱,而商品化的GC毛细管柱应用最多的是以含5%苯基的聚甲基硅氧烷为固定相的色谱柱。GC×GC发展迅猛,特别是关于调制器的研究,已开发出十多种调制模式,并广泛地应用于各个领域。为了适应大量样品的分析和现场分析,研究和开发了多种快速GC方法和仪器以及便携式GC仪。为了仪器的小型化和专属性检测,μGC仪的研究也稳步地发展起来。     

Proper Tuning of Comprehensive Two‐Dimensional Gas Chromatography (GC×GC) to Optimize the Separation of Complex Oil Fractions

Comprehensive two‐dimensional gas chromatography (GC×GC) is an utterly suitable separation technique for the analysis of complex samples, such as oil fractions. Once the two columns and the operating conditions are properly tuned, the technique is able to provide a detailed characterization of such materials. Some considerations applying to the tuning of a GC×GC system for a specific separation are presented and discussed. The authors present a number of different column sets and conditions which allow the separation of a non‐aromatic hydrocarbon solvent, a kerosene, the light end of a crude oil, and an olefinic fraction, respectively. The highly structured GC×GC chromatograms, together with chemical knowledge about the samples, provide a much more comprehensive characterization of the samples than hitherto possible.     

A Robust Thermal Modulator for Comprehensive Two-Dimensional Gas Chromatography

In comprehensive two-dimensional gas chromatography (GC×GC), two capillary columns are connected in series through an interface known as a “thermal modulator”. This device transforms effluent from the first capillary column into a series of sharp injection-like chemical pulses suitable for high-speed chromatography on the second column. Dramatic increases in the resolving power, sensitivity, and speed of the gas chromatograph result. This paper describes the development of a robust and reliable thermal modulator for GC×GC.     

Determination of Oxygenates in Gasoline by GC×GC

Comprehensive two‐dimensional gas chromatography (GC×GC) has been applied to the quantitation of oxygenates in reformulated gasoline. Target oxygenates were C₁–C₄ alcohols, tert‐pentanol, methyl tert‐butyl ether (MTBE), diisopropyl ether (DIPE), ethyl tert‐butyl ether (ETBE), and tert‐amyl methyl ether (TAME). These were separated from the gasoline matrix using a volatility‐based selectivity in the first chromatographic dimension, followed by a mixed‐phase polarity/shape selectivity in the second dimension. The high resolving power of this stationary phase combination completely separated all oxygenates except DIPE, ETBE, and TAME, which exhibited coelution with other nonpolar gasoline components. Oxygenates quantitation was achieved with the use of an internal standard, an FID detector, and calibration curves. Quantitation results are in good agreement with ASTM and EPA standard methods. When coupled with our previous method for BTEX and aromatics, a single GC×GC method can now quantitate MTBE, alcohols, BTEX, and aromatics in a one‐hour analysis.     

Comparison of Thermal Sweeper and Cryogenic Modulator Technology for Comprehensive Gas Chromatography

The two current technologies for achieving comprehensive gas chromatography (GC×GC) – the thermal sweeper and the cryogenic modulator – are compared in an interlaboratory study using a multicomponent semi‐volatile aromatic compound sample. The same column set (phases, film thickness, dimensions of columns) and conditions of oven temperature program were used. Carrier gas flow settings however were different for the data reported here. The thermal sweeper has a longer overall length due to the extra ca. 30 cm length of narrow bore tubing used for the modulator/accumulator section. Data reveal that the two methods behave in an analogous manner in respect of delivering GC×GC results, with key peak parameters of peak widths and symmetry measures showing good correlation. Retention time dissimilarity on the first dimension columns in the two systems arises from different flow rates used, however the second column retention is similar, and this is due to the resulting different elution temperatures that peaks elute on the first dimension in each system. Overall, the two approaches to GC×GC appear to produce equivalent results within the scope of the application studied. Each system does have its experimental limitations; the thermal sweeper has what may be called a ‘thick film effect’, where at high temperature it can be difficult to sufficiently trap the migrating bands in the accumulator column, and the pulsing of solutes in the cryogenic system may suffer from a ‘thick wall effect’ if a column with too thick a wall dimension is used at low oven temperature.     

Comprehensive two-dimensional gas chromatography (GC×GC) in environmental analysis and monitoring

Compared to conventional one-dimensional gas chromatography (1D-GC), comprehensive two-dimensional gas chromatography (GC×GC) offers increased peak capacity, improved resolution and enhanced mass sensitivity. In addition, it generates structured two-dimensional (2-D) chromatograms, which aids in the identification of compound classes. Sample preparation procedures can often be minimized, or even eliminated in some cases, due to the superior separating power offered by the technique. All of these advantages make GC×GC a very powerful tool in environmental analysis involving the determination of trace levels of toxic compounds in complex matrices. This review paper summarizes and examines the historical and recent GC×GC applications in environmental analysis and monitoring.     

生物制药研究中的多维色谱

对全二维气相色谱(GC×GC)、全二维液相色谱(HPLC×HPLC)、多维毛细管电泳等多维分离技术在生物制药研究中的应用进行了综述,其中对作者所在研究组在全二维气相色谱应用于中药及固相萃取-液相色谱联用分析系统等方面的工作做了重点介绍。由所综述的生物制药研究得出结论：多维分离方法以其高分辨、快速、自动化等特点已经在生物制药领域显示出它的巨大优势,并将发挥更大的作用。     

Modified semi-rotating cryogenic modulator for comprehensive two-dimensional gas chromatography

A previously constructed semi-rotating cryogenic modulator was modified for comprehensive two-dimensional gas chromatography (GC×GC). The retention time repeatability was improved by replacing the modulator control program unit with a new system. Peak widths obtained with the modified modulator were comparable with those obtained with the previous modulator and other modulator types. The modulator was easy to construct and it can be installed in any commercial GC system. The constructed GC×GC–FID system and data obtained by gas chromatography–mass spectrometry (GC–MS) were used for identification of unknowns in forest aerosol samples. Figure A semi-rotating cryogenic modulator in which modulation is based on two-step cryogenic trapping with continuously flowing carbon dioxide has been developed for comprehensive two-dimensional gas chromatography     

Quantitative Aspects of Comprehensive Two-Dimensional Gas Chromatography (GC×GC)

A software program was developed to enable the quantification of the complex 3D-data sets as produced by GC×GC. Using this software, it was demonstrated that the detectability limit of GC×GC in our study is 18 times better than that of ‘normal’ capillary gas chromatography (CGC). This enhancement is due to the signal increase produced by the thermal modulation effect. The relative standard deviation of 0.9% as measured on a test mixture was excellent. Furthermore, a comparison was made for the group-type separation of heavy gas oils between the hyphenation of LC and GC (LC-GC) and GC×GC. Although these separations are different in nature, the agreement of the results of both methods was very good. The results of GC×GC may even be more accurate, since, different from CGC, even in the most complex chromatograms the baseline in the second dimension chromatograms is always present.     

The role of sample preparation in multidimensional gas chromatographic separations for non‐targeted analysis with the focus on recent biomedical,food, and plant applications

In this review, we consider and discuss the affinity and complementarity between a generic sample preparation technique and the comprehensive two‐dimensional gas chromatography process. From the initial technical development focus (e.g., on the GC×GC and solid‐phase microextraction techniques), the trend is inevitably shifting toward more applied challenges, and therefore, the preparation of the sample should be carefully considered in any GC×GC separation for an overreaching research. We highlight recent biomedical, food, and plant applications (2016–July 2020), and specifically those in which the combination of tailored sample preparation methods and GC×GC–MS has proven to be beneficial in the challenging aspects of non‐targeted analysis. Specifically on the sample preparation, we report on gas‐phase, solid‐phase, and liquid‐phase extractions, and derivatization procedures that have been used to extract and prepare volatile and semi‐volatile metabolites for the successive GC×GC analysis. Moreover, we also present a milestone section reporting the early works that pioneered the combination of sample preparation techniques with GC×GC for non‐targeted analysis.     

Enhancing the Limit of Detection for Comprehensive Two‐Dimensional Gas Chromatography (GC×GC) using Bilinear Chemometric Analysis

The chemometric method referred to as the generalized rank annihilation method (GRAM) is used to improve the precision, accuracy, and resolution of comprehensive two‐dimensional gas chromatography (GC×GC) data. Because GC×GC signals follow a bilinear structure, GC×GC signals can be readily extracted from noise by chemometric techniques such as GRAM. This resulting improvement in signal‐to‐noise ratio (S/N) and detectability is referred to as bilinear signal enhancement. Here, GRAM uses bilinear signal enhancement on both resolved and unresolved GC×GC peaks that initially have a low S/N in the original GC×GC data. In this work, the chemometric method of GRAM is compared to two traditional peak integration methods for quantifying GC×GC analyte signals. One integration method uses a threshold to determine the signal of a peak of interest. With this integration method only those data points above the limit of detection and within a selected area are integrated to produce the total analyte signal for calibration and quantification. The other integration method evaluated did not employ a threshold, and simply summed all the data points in a selected region to obtain a total analyte signal. Substantial improvements in quantification precision, accuracy, and limit of detection are obtained by using GRAM, as compared to when either peak integration method is applied. In addition, the GRAM results are found to be more accurate than results obtained by peak integration, because GRAM more effectively corrects for the slight baseline offset remaining after the background subtraction of data. In the case of a 2.7‐ppm propylbenzene synthetic sample the quantification result with GRAM is 2.6 times more precise and 4.2 times more accurate than the integration method without a threshold, and 18 times more accurate than the integration method with a threshold. The limit of detection for propylbenzene was 0.6 ppm (parts per million by mass) using GRAM, without implementing any sample preconcentration prior to injection. GRAM is also demonstrated as a means to resolve overlapped signals, while enhancing the S/N. Four alkyl benzene signals of low S/N which were not resolved by GC×GC are mathematically resolved and quantified.     

全二维气相色谱在食品风味化学成分分析中的应用

食品风味是评价食品品质特征的重要指标。食品风味物质分析通常采用一维气相色谱或气相色谱-质谱联用法,但由于某些食品风味成分组成和基质复杂,无法用一维气相色谱将其完全分离。全二维气相色谱将分离机理不同而又相互独立的两根色谱柱以正交方式组合,显著提升了色谱分离能力和分析速度,可满足食品中风味化学成分的二次分离。该文综述了全二维气相色谱技术在未经二次加工的食用农产品(如水果、蔬菜和肉类)和经过二次加工的食品(如乳制品、饮品和调味品)中风味化学成分分析中的应用,展现了全二维气相色谱技术的特点,并为食品风味的解析提供参考。     

Separation and screening of short-chain chlorinated paraffins in environmental samples using comprehensive two-dimensional gas chromatography with micro electron capture detection

Short-chain chlorinated paraffins (SCCPs) are highly complex technical mixtures with thousands of isomers and numerous homologs. They are classified as priority candidate persistent organic pollutants under the Stockholm Convention for their persistence, bioaccumulation, and toxicity. Analyzing SCCPs is challenging because of the complexity of the mixtures. Chromatograms of SCCPs acquired using one-dimensional (1D) gas chromatography (GC) contain a large characteristic “peak” with a broad and unresolved profile. Comprehensive two-dimensional GC (GC×GC) shows excellent potential for separating complex mixtures. In this study, GC×GC coupled with micro electron capture detection (μECD) was used to separate and screen SCCPs. The chromatographic parameters, including the GC column types, oven temperature program, and modulation period, were systematically optimized. The SCCP congeners were separated into groups using a DM-1 column connected to a BPX-50 column. The SCCP congeners in technical mixtures were separated according to the number of chlorine substituents for a given carbon chain length and according to the number of carbon atoms plus chlorine atoms for different carbon chain lengths. A fish tissue sample was analyzed to illustrate the feasibility of the GC×GC–μECD method in analyzing biological samples. Over 1,500 compounds were identified in the fish extract, significantly more than were identified using 1D GC. The detection limits for five selected SCCP congeners were between 1 and 5 pg/L using the GC×GC method, and these were significantly lower than those achieved using 1D GC. This method is a good choice for analysis of SCCPs in environmental samples, exhibiting good separation and good sensitivity. Graphical Abstract

Chromatograms of a technical C10–C13 SCCP mixture with a 55 % (w/w) chlorine content obtained using a gas chromatography–electron capture detection (ECD) and b GC×GC–μECD     

Application of solid-phase micro-extraction and comprehensive two-dimensional gas chromatography (GC×GC) for flavour analysis

Summary Headspace solid-phase micro-extraction (HS SPME), comprehensive two-dimensional GC (GC×GC), and flame ionization detection (FID) have been examined for their suitability and compatibility for rapid sampling, separation, and detection of garlic flavour volatiles. This approach (HS-SPME-GC×GC-FID) is distinctly superior to use of one-dimensional GC, i. e., HS-SPME-GC-FID. Direct comparison of the experimental results showed that a 10–50-fold increase in sensitivity is obtained, separating power is substantially enhanced, and the peak capacity is up to ten times higher. As a consequence, much more detailed flavour analysis can be performed; this results in better information about the aroma-active compounds.     

Design and Implementation of Comprehensive Gas Chromatography with Cryogenic Modulation

Comprehensive gas chromatography is the realization of true continuous multidimensional (dual column) gas chromatography. The key requirement in the comprehensive GC experiment is that the second dimension analysis is completed in a rapid time‐frame compared to the elution of components in the first dimension, and that the two coupled dimensions represent ‘orthogonal’ analyses towards the analytes to be separated. The former normally necessitates pulsing of contiguous segments of each chromatographic band from the first to the second dimensions. The two dimensions should be in fluid communication. The comprehensive GC×GC experiment passes all the column flow from the first column to the second column, leading to no sample loss, but this also requires a suitable method for time‐ or zone‐compression of the band to be pulsed to the second column. The final pulse should be narrow, and should be delivered to the second column quickly. A simple procedure can achieve this using the cryogenic modulator that has been recently described by this group. The system uses a cryogenic trap which can be moved away from the cooled zone of the column faster than 10 ms. A fast‐acting pneumatic ram achieves this performance. The cooled column heats up to the prevailing oven temperature within 10–15 ms. Molecules as volatile as C5 alkanes or small aromatics will be fully retained by the trap within the period of modulation used for GC×GC. The technique is simple to implement and requires no special column connections. Using a gas chromatograph which allows control of external events and can acquire from a detector at 50 Hz or faster, and a timing controller for modulation, the comprehensive result can easily and effectively be achieved.     

A New Pulsed Flow Modulation GC × GC–MS with Cold EI System and Its Application for Jet Fuel Analysis

We designed and operated a new system of pulsed flow modulation (PFM) two dimensional comprehensive gas chromatography (GC × GC) mass spectrometry (MS). This system is based on the combination of PFM–GC × GC with a quadrupole mass spectrometer of GC–MS via a supersonic molecular beams interface and its fly-through Cold EI ion source and applied this system for the analysis of JP8 jet fuel. PFM is a simple GC × GC modulator that does not consume cryogenic gases while providing tunable second GC × GC column injection time for enabling the use of quadrupole based mass spectrometry regardless its limited scanning speed. We analyzed JP8 jet fuel with our new PFM–GC × GC–MS with Cold EI system and found that as the second dimension GC elution time is increased the observed molecular ion mass is reduced. This unique observation that helped in improved sample compounds identification under co-elution conditions was enabled via having abundant molecular ions in Cold EI for all the fuel compounds. We named this type of analysis as PFM–GC × GC × MS. We found and discuss in this paper that PFM–GC × GC–MS with Cold EI combines improved separation of GC × GC with Cold EI benefits of tailing-free ultra-fast ion source response time and enhanced molecular ions and mass spectral isomer and isotope information for the provision of increased sample identification information.