Effect of first-dimension column film thickness on comprehensive two-dimensional gas chromatographic separation

In comprehensive two-dimensional gas chromatography (GC x GC), samples experience two-dimensional separation implemented by a modulator which helps preserve the first-dimension separation and facilitates the second-dimension separation by periodically collecting, focusing and launching the material from the primary column onto the secondary column with a different stationary phase. Column overloading in GC x GC is a considerable problem, aggravated by the fact that two columns are involved. Broad first-dimension peaks of an analyte help produce smaller fractions of the analyte in the second-dimension, reducing the chance of secondary column overloading. One of the means to generate broad peaks in the first-dimension is to use thick film primary columns. A series of primary columns of various film thickness were tested in the study, and the results indicate that when other conditions are kept constant, 1 microm film columns often provide better resolution in both first and second-dimension but at the expense of a much longer separation time; 0.1 microm is clearly inadequate for GC x GC separation; 0.5 and 0.25 microm film columns seem to be the best compromises.     

Comprehensive two-dimensional gas chromatography with isotope dilution time-of-flight mass spectrometry for the measurement of dioxins and polychlorinated biphenyls in foodstuffs. Comparison with other methods

A comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC x GC-TOF-MS) experimental setup was tested for the measurement of seven 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs), ten 2,3,7,8-substituted polychlorinated dibenzofurans (PCDFs), four non-ortho-polychlorinated biphenyls (PCBs), eight mono-ortho-PCBs, and six indicator PCBs (Aroclor 1260) in foodstuff samples. A 40m RTX-500 (0.18mm I.D., 0.10 microm df) was used as the first dimension (1D) and a 1.5 m BPX-50 (0.10mm I.D., 0.10 microm df) as the second dimension (2D). The GC x GC chromatographic separation was completed in 45 min. Quantification was performed using 13C-label isotope dilution (ID). Isotope ratios of the selected quantification ions were checked against theoretical values prior to peak assignment and quantification. The dynamic working range spanned three orders of magnitude. The lowest detectable amount of 2,3,7,8-TCDD was 0.2 pg. Fish, pork, and milk samples were considered. On a congener basis, the GC x GC-ID-TOF-MS method was compared to the reference GC-ID high resolution mass spectrometry (HRMS) method and to the alternative GC-ID tandem-in-time quadrupole ion storage mass spectrometry (QIST-MS/MS). PCB levels ranged from low picogram (pg) to low nanogram (ng) per gram of sample and data compared very well between the different methods. For all matrices, PCDD/Fs were at a low pg level (0.05-3 pg) on a fresh weight basis. Although congener profiles were accurately described, RSDs of GC x GC-ID-TOF-MS and GC-QIST-MS/MS were much higher than for GC-ID-HRMS, especially for low level pork and milk. On a toxic equivalent (TEQ) basis, all methods, including the dioxin-responsive chemically activated luciferase gene expression (DR-CALUX) assay, produced similar responses. A cost comparison is also presented.     

Search criteria and rules for comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry analysis of airborne particulate matter

Direct thermal desorption-gas chromatography-time-of-flight mass spectrometry (DTD-GC-TOFMS) and comprehensive two-dimensional (2D) gas chromatography-time-of-flight mass spectrometry (GC x GC-TOFMS) was applied for characterisation of semi-volatile organic compounds (SVOC) in fine particulate matter (PM), with a diameter of up to 2.5 microm (PM2.5), from ambient air in Augsburg, Germany. DTD-GC-TOFMS measurements on the SVOC in PM2.5 are done on a daily basis (time series over several years). The data will be used in an epidemiological study questioning the influence of SVOC in PM2.5 on ambient aerosol related health effects. The outcome of the first measurements periods is that the organic inventory in the ambient aerosol can undergo drastic fluctuations, e.g. due to meteorological influences or specific emission sources. This includes also the large fraction of chromatographically not resolved peaks (unresolved carbonaceous matter (UCM)). The UCM fraction contains about 70% of the SVOC mass in PM2.5. GC x GC-TOFMS is a suited technique to study the nature of the yet unidentified compounds forming the UCM. The considerably increased chromatographic resolution in GC x GC allows separation of many UCM compounds while the TOFMS supplies mass spectral data of all separated compounds. However, the data sets are getting enormously complex. In a typical PM2.5 sample from Augsburg more than 15,000 peaks can be detected. Thus, it is important to classify the observed GC x GC peaks by rational means. A classification procedure based on GC x GC retention times and the fragmentation patterns is suggested. With a preliminary classification procedure it is already possible to group compounds with some certainty into substance classes. After some further development, this approach can be used for classifying GC x GC data, e.g. for environmental and epidemiological studies.     

Fast analysis of decabrominated diphenyl ether using low-pressure gas chromatography-electron-capture negative ionization mass spectrometry

This paper reports the applicability of low-pressure gas chromatography-mass spectrometry operated in electron-capture negative ionization mode (LP-GC-ECNI-MS) for the analysis of decabrominated diphenyl ether (BDE-209). Particular attention was paid to find optimal injector and oven conditions for minimal thermal degradation of BDE-209. The analytical characteristics were compared for LP-GC columns (10 m x 0.53 mm) with different film thicknesses (d(f) 0.15 microm versus 0.25microm) and for a conventional GC column (15 m x 0.25 mm, 0.10 microm d(f)). Short residence times (6.5 and 9.8 min) of BDE-209 were found for the LP-GC systems with 0.15 and 0.25microm d(f), respectively, resulting in a low elution temperature and minimal degradation. Additionally, baseline separation of 22 polybrominated diphenyl ether (PBDE) congeners (major components of PBDE technical mixtures) was possible in less than 12 min using the LP-GC-ECNI-MS system with 0.15microm d(f). The optimized method was applied for the determination of PBDEs in Belgian indoor dust samples. The obtained concentrations of BDE-209 (range 8-292 ng/g dry weight) were in the same range or lower than concentrations in dust from other European countries.     

Development and evaluation of gold-centered monolayer protected nanoparticle stationary phases for gas chromatography

The current status for the development of novel open-tubular gas chromatography (GC) stationary phases consisting of thin films of gold-centered monolayer protected nanoparticles (MPNs) is reported. Dodecanethiol MPNs, in which the monolayer is dodecanethiol linked to the gold nanoparticle, have shown great promise as a GC stationary phase with efficient columns having been produced in a variety of capillary i.d.'s with stationary phase film depths ranging from 10 to 60 nm, +/-2 nm at a given film depth. Stationary phase operational parameters are discussed including maximum operating temperature, sample capacity, and stationary phase lifetime and robustness. An overview of the general method employed for column production is also included. The sample capacity was determined for a 2.5 m, 250 microm i.d. column with a stationary phase film thickness of 40 nm, at 50 degrees C using anisole (k' = 1.86) as the probe analyte. The sample capacity was experimentally found to be 2.3 ng under these conditions, similar to values reported for thicker, polymer stationary phases. The efficiency of the dodecanethiol MPN stationary phase was determined with a 100 microm i.d. capillary and found to have a reduced plate height hmin value of 0.95 for octane (k' = 0.68). Areas of application illustrated and discussed utilizing the dodecanethiol MPN stationary phase include complementary separations such as two-dimensional GC (GC x GC), potential utilization within a model system for a micro-fabricated GC (microGC), as well as efficient single dimension high-speed separations. Initial development of polar stationary phases utilizing 4-chlorobenzenethiol MPNs and 4-(trifluoromethyl)benzenethiol MPNs is discussed. Included is a selectivity comparison of the retention behavior of the 4-chlorobenzenethiol MPN stationary phase and the dodecanethiol MPN stationary phase.     

Characterization and utilization of a novel triflate ionic liquid stationary phase for use in comprehensive two-dimensional gas chromatography

A novel triflate (trifluoromethylsulfonate) ionic liquid (IL) thin film (0.08 microm) stationary phase was implemented for use within the second column of a comprehensive GC x GC configuration. The first column in the configuration had a 5% phenyl/95% dimethyl polysiloxane (DMPS) stationary phase with a 0.4 microm film. The DMPS x IL column configuration was used to separate a mixture of 32 compounds of various chemical functional classes. The GC x GC results for the IL column were compared with a commercially available polar column (with a 0.1 microm PEG stationary phase film) used as the second column instead. Additional studies focused on the rapid and selective separation of four phosphorous-oxygen (P-O) containing compounds from the 32-compound matrix: dimethyl methylphosphonate (DMMP), diethyl methylphosphonate (DEMP), diisopropyl methylphosphonate (DIMP), and triethyl phosphate (TEP). van't Hoff plots (plots of ln k vs. 1/T) demonstrated the difference in retention between the P-O containing compounds (with DMMP reported in detail) and other classes of compounds (i. e., 2-pentanol and n-dodecane as representative) using either the IL column or the commercial PEG column. The selectivity (alpha) of the triflate IL column and the commercially available PEG column were also compared. The IL column provided significantly larger selectivities between DMMP and the other two compounds (2-pentanol and n-dodecane) than the commercial PEG column. The alpha for DMMP relative to n-dodecane was 3.0-fold greater for the triflate IL column, and the alpha for DMMP relative to 2-pentanol was 1.7-fold greater for the triflate IL column than for the PEG column.     

色谱与色谱/质谱法相结合分析热裂解汽油C9馏分

采用毛细管气相色谱-氢火焰离子化检测器（CGC-FID）和气相色谱-质谱法(GC/MS)分析了热裂解汽油C9 馏分的组成。实验使用PONA毛细管气相色谱柱(100 m×0.25 mm i.d.×0.5 μm),根据烃类化合物在PONA柱上的保留规律,以正构烷烃标样保留值作为碳数分布依据,定量分析了裂解汽油C9 馏分中烃类化合物的碳数分布和单体烃含量;用GC/MS联用技术和CGC保留值定性法相结合对裂解汽油C9 馏分中相对含量大于0.2%的39种化合物进行了定性。     

Qualitative evaluation of thermal desorption-programmable temperature vaporization-comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry for the analysis of selected halogenated contaminants

The separation of 38 toxic and predominant polychlorinated biphenyl (PCB) congeners, 11 persistent halogenated pesticides, 1 brominated biphenyl (BB), and 8 polybrominated diphenyl ethers (PBDEs) has been optimized using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC x GC-TOFMS). A thermal desorption-programmable temperature vaporization (TD-PTV) step was used for the injection. Different column sets were investigated, and a 100% dimethylpolysiloxane (15 m x 0.25 mm i.d. x 0.25 microm film thickness) narrowbore capillary column coupled to a high temperature (8% phenyl)-polycarborane-siloxane (2 m x 0.10 mm i.d. x 0.10 microm film thickness) microbore column set was selected. Of the 58 compounds investigated, only one pair of PCBs was not resolved. All other analytes were either baseline separated into the chromatographic plane or were virtually separated using the deconvolution capability of the TOFMS.     

Flow regime at ambient outlet pressure and its influence in comprehensive two-dimensional gas chromatography

With method development in one-dimensional GC already being a tedious task, developing GC x GC methods is even more laborious. The majority of the present GC x GC applications are derived from previously optimised 1D-GC methods, from which especially the carrier gas flow settings are copied. However, in view of the high pressure inside the first-dimension column (high flow resistance of the narrow-bore second-dimension column), diffusion in the first column is much slower than in 1D-GC. Proper optimisation of the column combination and the carrier gas flow can considerably improve separations in GC x GC. To assist in the process of selecting column dimensions and flow rate optimization, we have developed a computer programme, based on Excel, that enables quick and simple calculation for all types of column combinations. The programme merely needs column dimensions and carrier gas type as input parameters and calculates all resolution and velocity parameters of the GC x GC separation by using flow rate and plate height equations. From the calculations a number of interesting conclusions can be drawn. As an example, the calculations clearly show that the majority of column combinations reported up till now have been operated at a far from optimal flow -- and, consequently, a far from optimal resolution. Probably even more important is the conclusion that the majority of column combinations used so far, i.e. those with 100 microm I.D. second-dimension columns, are not necessarily the best choice for GC x GC.     

辛硫磷和氯氰菊酯的大口径毛细管气相色谱定量分析研究

 对辛硫磷和氯氰菊酯的复配农药——２０％辛氯乳油进行了气相色谱定量分析的研究。以甲基对硫磷为内标,使用大口径毛细管柱,采用快速程序升温、高载气流速等手段,解决了辛硫磷高温易分解与氯氰菊酯色谱流出温度高的矛盾。在相同的色谱条件下对二者进行定量分析,变异系数分别为０．６７％和１．０％。方法简便、快速、准确。     

Determination and quantification of sulfadiazine and trimethoprim in swine tissues using liquid chromatography with ultraviolet and mass spectrometric detection

High-performance liquid chromatographic procedures with ultraviolet detection were developed for the quantitative determination of sulfadiazine (SDA) and trimethoprim (TMP) in swine tissues (kidney, liver, muscle, fat and fat + skin). In addition, high-performance liquid chromatography with atmospheric pressure chemical ionization mass spectrometry was used for the confirmation of the identity of the analytes of interest. Chromatographic separation was achieved on a Spherisorb ODS-2 column (250 x 4.6 mm id, dp 5 microns). The mobile phase for SDA analysis consisted of 1% acetic acid in water-acetonitrile (85 + 15, v/v). For TMP analysis a 80 + 15 + 5 (v/v/v) mixture of 0.25% triethylammonium acetate in water, acetonitrile and methanol was used as the eluent. Sulfamerazine and ormethoprim were used as the internal standards for SDA and TMP analysis, respectively. For the isolation of the compounds of interest from biological samples, a liquid-liquid extraction with acetone and ethyl acetate, followed by a clean-up using a solid-phase extraction column (aminopropyl and benzenesulfonic acid for SDA, benzenesulfonic acid for TMP) was performed. Calibration graphs were prepared for all tissues and linearity was achieved over the concentration ranges tested (50-1000 ng g-1 for SDA, r > or = 0.9979; 25-500 ng g-1 for TMP, r > or = 0.9994). The method was validated at the maximum residue level (MRL, 100 ng g-1 for SDA and 50 ng g-1 for TMP), at half the MRL and at double the MRL for both SDA and TMP. The accuracy and precision (expressed as the within-day repeatability) were found to be within the required ranges for each specific concentration. The quantification limits were 50 ng g-1 for SDA and 25 ng g-1 for TMP. The limits of detection were below one half the MRLs. Both methods were selective for the determination of SDA and TMP. Biological samples (kidney, liver, muscle, fat and fat + skin) from pigs that received a commercial SDA-TMP preparation with the feed for five consecutive days (dose rate: 25 mg SDA and 5 mg TMP kg body weight-1 day-1) were analyzed using the described methods. The quantitative results were used to calculate a withdrawal time (12 days) to reach residue levels below the respective MRLs. This calculation was performed according to the recommendations of the European Agency for the Evaluation of Medicinal Products (EMEA/CVMP/036/95).     

Ultra-fast essential oil characterization by capillary GC on a 50 microm ID column

A 5 m x 50 microm capillary column with 0.05 microm stationary phase film thickness, with a calculated efficiency of almost 20,000 plates per metre (under optimum conditions), was used for very fasthigh resolution GC analysis of lime essential oil. The total analysis time of this volatile essential oil was less than 90 s. Fast GC is shown to be appropriate for essential oil quality assurance analysis, and quantitative results of key components are comparable with those obtained by using conventional GC analysis. The fast GC analysis is approximately 33 times faster than the conventional GC method.     

Determination of petroleum contamination in shellfish using solid phase micro-extraction with gas chromatography-mass spectrometry

Headspace solid phase micro-extraction (HS-SPME) has been applied as a sampling technique for the determination of petroleum contamination in shellfish using capillary gas chromatography-mass spectrometry (GC-MS). A poly(dimethylsiloxane) fused silica fibre (100 microm thickness) was found to be satisfactory for the extraction of a range of aliphatic hydrocarbons (HCs) from homogenised shellfish tissues. The SPME conditions, including temperature, salt content, extraction time and desorption temperature, were optimised for a range of aliphatic HCs (C9-C20). A methyl silicone column GC (12 m x 0.20 mm, 0.33 microm layer thickness) was used with a temperature programme from 40 to 260 degrees C and the HCs were determined within a mass range of m/ z=50-550 in electron impact mode. Calibration range was from 10 to 5000 ng/g with linear correlation coefficients ( r(2)) of 0.982 for nonane to 0.997 for octadecane. Detection limits for aliphatic HCs, spiked into shellfish (mussel) tissues, varied from 3.6 ng/g (tetradecane) to 51 ng/g (eicosane) and relative standard deviation (% RSD) values ranged from 1.4% (hexadecane) to 24.3%(eicosane).     

Analysis of methoxypyrazines in wine using headspace solid phase microextraction with isotope dilution and comprehensive two-dimensional gas chromatography

This study reports an optimized headspace-solid phase microextraction (HS-SPME) method for the determination of methoxypyrazines in wine. Analysis was performed by using comprehensive two-dimensional gas chromatography with novel detection capabilities, including nitrogen phosphorus detection (GC x GC-NPD) and time-of-flight mass spectrometry (GC x GC-TOFMS). In the latter, stable isotope dilution was performed for the quantitation of 2-methoxy-3-(2-methylpropyl) pyrazine (IBMP), using labelled 2-(2H3)methoxy-3-(2-methylpropyl)pyrazine (d3-IBMP) as the internal standard, and resolution of the two analogues was facilitated using the deconvolution capabilities of the TOFMS. This research represents the first report of HS-SPME with isotope dilution and GC x GC-TOFMS (GC x GC-IDTOFMS). Analysis by GC x GC-NPD enabled detection limits of 0.5 ng/L for the quantitation of IBMP, which was superior to that obtained using GC x GC-IDTOFMS (1.95 ng/L). Nevertheless, both methods were adequately sensitive for real wine analysis, yielding highly comparable IBMP concentrations of 26.1 and 27.8 ng/L, respectively, from a Sauvignon blanc wine. The complexity of the real wine headspace was simplified as a result of selective detection using GC x GC-NPD and, in the case of GC x GC-IDTOFMS, the use of extracted ion chromatograms (EICs).     

Overloading of the second-dimension column in comprehensive two-dimensional gas chromatography

Comprehensive two-dimensional gas chromatography (GC x GC) is based on a coupling of two GC columns of different characteristics by means of a device that allows portions of the effluent from the primary column to be injected onto the second dimension column for an additional separation. The time available for the separation in the second-dimension column is very short. Thus, this separation should be very efficient. The vast majority of GC x GC practitioners use very narrow bore columns for the second dimension. While this approach is justified in principle, if peaks in the second dimension overload this column, its peak capacity is severely reduced. A series of second-dimension columns of varying internal diameters, but similar phase ratios, were used to study these effects. The results indicate that 250 microm columns often provide comparable second dimension peak widths to 100 microm columns, while at the same time being less prone to overloading, indicating that they may often be a better choice than smaller diameter columns in the second dimension of GC x GC systems.     

Simultaneous quantification of sulfamethoxazole and trimethoprim in whole egg samples by column-switching high-performance liquid chromatography using restricted access media column for on-line sample clean-up

This work reports the application of restricted access media (RAM) column, in a multidimensional configuration, for simultaneous analysis of sulfamethoxazole (SMX) and trimethoprim (TMP) in whole eggs with ultraviolet detection. The proteins were partially precipitated by adding 0.5 mL of acetonitrile into 1.0 mL of blended egg followed by centrifugation. The supernatant was injected (250 microL) directly into the multidimensional system. At the first dimension, a restricted access medium (RAM) bovine serum albumin (BSA) octadecyl column (100 mm x 46 mm I.D., Luna silica, 10 microm particle size and 100 A pore size), was used for extraction and concentration of the analytes and at second dimension, an octadecyl column (150 mm x 46 mm I.D., Luna silica, 10 microm particle size and 100 A pore size), for analysis. The developed method showed good selectivity, accuracy and precision for quantification of these different compounds in eggs, and the limits of quantification were 80 ng/mL, for both compounds. The validated method is reliable and sensitive for monitoring residues in whole eggs samples and thus, to determine withdraw period for laying hens using veterinary medicine having SMX-TMP combination.     

气相色谱/氢火焰离子化检测法分析烷基化物料中的C4氟代烃

以实验室合成的氟代叔丁烷、氟代仲丁烷、氟代正丁烷为参考,建立了烷基化物料中C4氟代烃的气相色谱/氢火焰离子化检测(GC/FID)分析方法。提出了利用气相色谱/原子发射光谱(GC/AED)按元素响应的特点求算C4氟代烃在GC/FID上相对校正因子的方法。方法采用OV-225(50 m×0.25 mm i.d.×0.25 μm)和SE-54(44 m×0.22 mm i.d.×0.25 μm)串联柱为分析柱,FID为检测器,校正归一化或间接外标方法进行定量,具有重复性好、应用移植便利、操作简单等特点,对氟代叔     

气相色谱法同时测定蟛蜞菊中的蟛蜞菊倍半萜内酯A和B

蟛蜞菊具有抗肿瘤、抗病毒作用,其主要活性成分是倍半萜内酯类物质。以分离纯化所得的结晶倍半萜内酯A与B为参考标准,采用HP毛细管色谱柱(30 m×0.25 mm i.d.× 0.25 μm),程序控制升温,氢火焰离子化检测器检测,测定了蟛蜞菊的地上部分（茎叶和花）中倍半萜内酯A与B的含量。测定结果表明:蟛蜞菊茎叶中的倍半萜内酯A和B的含量分别为（239±6.4） μg/g和（156±15） μg/g;花中倍半萜内酯A和B的含量分别为（233±6.5） μg/g和（173±16） μg/g。该法可用于蟛蜞菊原料及其药品的质量控制。     

Evaluation of low-pressure gas chromatography linked to ion-trap tandem mass spectrometry for the fast trace analysis of multiclass pesticide residues

A rapid multiresidue method for the analysis of 72 pesticides has been developed using a single injection with low-pressure gas chromatography/tandem mass spectrometry (LP-GC/MS/MS). The LP-GC/MS/MS method used a short capillary column of 10 m x 0.53 mm i.d. x 0.25 microm film thickness coupled with a 0.6 m x 0.10 mm i.d. restriction at the inlet end. Optimal LP-GC conditions were determined which achieved the fastest separation in MS/MS detection mode. Also MS/MS conditions were optimized in order to increase sensitivity and selectivity. The analytical parameters of the LP-GC/MS/MS method were compared with those obtained by GC/MS/MS using a conventional capillary column (30 m x 0.25 mm i.d. x 0.25 microm film thickness). Better precision and sensitivity values were obtained with the LP-GC/MS/MS approach. The limits of detection (LOD) of the compounds ranged from 0.1 to 14.1 microg L(-1) for LP-GC/MS/MS, lower than those obtained for conventional GC/MS/MS that ranged from 0.1 to 17.5 microg L(-1). The peak widths obtained with the short column in LP-GC are similar to those obtained using conventional capillary GC columns, and the peaks can be successfully identified by MS/MS detection with the conventional scan speed of ion-trap instruments. In addition, the analysis time was significantly reduced with LP-GC/MS/MS (32 min) versus GC/MS/MS (72 min), allowing the number of samples analyzed per day in a routine laboratory to be doubled.     

Universal and discriminative detection using a miniaturized pulsed discharge detector in comprehensive two-dimensional GC

A miniaturized pulsed discharge detector (Mini-PDD) has been successfully demonstrated for comprehensive 2-D GC (GC x GC) analysis of pyrolysis gasoline and the pyrolysis GC x GC analysis of a polyethylene copolymer. The detector cell volume of the Mini-PDD is reduced to 25% of the Valco plug-in PDD D-3. An n-C11 peak width at base is 96 ms for the Mini-PDD, about 23% larger than a peak width of 78 ms detected by a flame ionization detector (FID). The Mini-PDD has sufficient response time for most GC x GC applications. When Mini-PDD is operated in helium photoionization mode (Mini He-PDD), it is a universal detector for both inorganic and organic compounds. This is especially useful when detection of water is needed in GC x GC applications. When krypton is doped in the helium discharge gas (Mini Kr-PDD), it can suppress signals of compounds having higher ionization potentials and enhance relative signal intensities of aromatic compounds. The determination of aliphatic to aromatic hydrocarbon ratios is essential to the operation of petroleum crackers. Comparison of the signal from two modes of the Mini-PDD is a simple and fast way to verify the location of aromatics in comprehensive 2-D gas chromatograms.