Wide-bore Column Research Articles

Boosting the odour perception of trace compounds exploiting three-dimensional GC-O with MS/FID simultaneous detection

ABSTRACT The study describes the effectiveness of a 3D GC system coupled with olfactometric detection and simultaneous MS and FID (3DGC-O-MS/FID) to improve the detection of odorants. Mega-bore columns were used to ensure a sample capacity able to enhance the odour perception. The heart-cut approach allowed to overcome the low efficiency of wide-bore columns, granting to purify enriched target fractions before olfactometry detection. After the third GC dimension, the isolated target peaks were eluted to the olfactometric port allowing the odour to last multiple seconds, making the panelist’s perception easier and more comfortable. The simultaneous FID/MS detection after the third GC dimension allowed to match specific odours to target molecules and their concentration in the sample. The 3DGC-O-MS/FID system boosts odour perception of trace components compared to conventional GC-O approaches. A reduced detection threshold of mg/kg levels was obtained compared to the mg/kg levels typical of monodimensional GC-O.

A dilute-and-inject low-pressure gas chromatography-tandem mass spectrometry method for phthalate determination in extra virgin olive oil.

The goal of this study was to develop a method for the determination of nine phthalic acid esters in extra virgin olive oils using low-pressure gas chromatography-triple-quadrupole mass spectrometry. Sample preparation was simple, environmental friendly, and rapid inasmuch that it involved only dilution(<1mL of hexane). The low-pressure gas chromatography analyses were performed by using a 5 m wide-bore column. The limit of quantification for the phthalates ranged from 0.06 to 1.14mg kg-1 . Both intra- and interday precisions were measured, with coefficient of variation values ranging from 0.2% to 11.7%. The trueness of the method was measured by evaluating accuracy at the initial stage of the work and after 2 months, with values ranging between -8.7% and 12.1%. Moreover, blind accuracy was comprised between -11.6% and 14.2%. The method involves the use of simplified instrumentation and reduced analysis times (nearly two times faster) compared to a previously published comprehensive two-dimensional gas chromatography-triple-quadrupole mass spectrometry method, leading to a reduction of energy and helium consumption. The approaches were compared in analytical terms and for the environmental impact. In total, 23 olive oil samples were analyzed, with at least one phthalate detected in all but one sample.

Comprehensive two-dimensional gas chromatography under low-pressure conditions

The analysis of thermally labile and high-boiling point compounds by gas chromatography (GC) can be a challenge. One technique to overcome these challenges is low-pressure GC, which uses the vacuum produced from the mass spectrometer and wide-bore columns to elute compounds at significantly lower temperatures. While GC-MS is a powerful technique, comprehensive two-dimensional gas chromatography (GC × GC), allows for resolution of compounds that would typically coelute using GC. In this study, a pesticide standard mixture (8270 MegaMix Standard) was analyzed using a conventional GC × GC-TOFMS configuration (0.25 mm inner diameter (i.d.) to a 0.18 mm i.d. column) and low-pressure GC × GC-TOFMS configuration (0.53 mm i.d. to a 0.53 mm i.d. column). Elution temperatures, sensitivity, and peak capacity were investigated for both configurations. Compounds eluted an average of 30 °C less on the low-pressure GC × GC-TOFMS configuration compared to the conventional GC × GC-TOFMS configuration. Moreover, the compounds were separated in ∼13 min on the low-pressure GC × GC-TOFMS as opposed to 33 min for conventional GC × GC-TOFMS. However, due to the wide-bore columns and faster runtimes the low-pressure GC × GC-TOFMS had a lower, β corrected 2D peak capacity, nc,β,2D, of 1260 while the conventional GC × GC-TOFMS was 3588. Interestingly, both configurations yielded a similar peak capacity production of 93 peaks/min and 107 peaks/min for low-pressure and conventional GC × GC-TOFMS, respectively. A “real world” sample of diesel fuel was tested on the low-pressure and conventional GC × GC-TOFMS configurations and similar results were obtained compared to the pesticide standard mix except the peak capacity production of the low-pressure GC × GC-TOFMS configuration was higher than that of the conventional GC × GC-TOFMS method.

Expanding the Knowledge Related to Flavors and Fragrances by Means of Three-Dimensional Preparative Gas Chromatography and Molecular Spectroscopy

As universally known, gas chromatography (GC) coupled with mass spectrometry (MS) allows us to acquire spectra that can be searched in specific databases to attain qualitative information on a peak of interest. When not present in databases, structure elucidation is required before including a new component in a library: from that moment, scientists all around the world will be able to identify the new molecule with analytical confidence after GC-MS analysis. Conversely, if data are not shared in commercial databases, even if a molecule is studied and elucidated, it appears to be unknown or only identifiable on the basis of third-party data taken from the literature, which is a serious limitation. The present paper deals with a case that confirms this assumption. A component of Myrtus communis L. volatile fraction was tentatively identified based on literature data. Despite this, reliable identification could not be achieved due to the lack of a corresponding spectrum in commercial MS databases. Afterwards, the target component was isolated in a reasonable quantity and with a high degree of purity for downstream characterization by spectroscopic techniques. For this purpose, preparative (prep) GC may appear insufficient for the isolation of volatile components from highly complex samples. In this study, a prep-MDGC system was implemented for the isolation of the compound of interest from myrtle oil, consisting of three wide-bore columns of different selectivity coupled by means of Deans switch transfer devices. Based on the NMR and GC-FTIR data acquired, the unknown compound was identified as 2,2,5,5,7,7-hexamethyl-3,7-dihydro-1-benzofuran-4,6(2H,5H)-dione. Noticeably, this is a known molecule, yet its mass spectrum had never been registered into MS databases and thus was not available to the scientific community. Finally, the spectrum was included for the first time in a commercial library, namely the FFNSC 5.0 MS database. The aim of the present study was to highlight the opportunity to make analytical data quickly available in a reliable way by registering them in searchable MS databases to improve the identification means for researchers all over the world.

Analysis of chemical components of Chinese medicine Ligustici Radix by achiral-chiral liquid chromatography-predictive multiple reaction monitoring

中药毛前胡为伞形科植物短片藁本Ligusticum brachylobum Franch.的干燥根,主要用于治疗风热咳嗽痰多、痰热喘满、咯痰黄稠等证,富含香豆素类化学成分,含有多组对映异构体和非对映异构体。为了深入研究毛前胡的化学成分组成,特别是对映异构体的组成,研究建立了非手性-手性色谱-预测多反应监测法(achiral-chiral-LC predictive MRM),同步实现毛前胡化学成分的化学选择性和立体选择性分离,以及高灵敏度定性分析。非手性色谱和手性液相色谱-串联质谱系统结合了RP-C18色谱柱的高效化学选择性分离能力以及手性色谱柱的立体选择性优势,有效避免了中心切割非手性-手性二维液相色谱构造复杂、重现性难以满足定量要求等缺陷。采用小内径核-壳型RP-C18色谱柱作为前端化学分离柱,实现结构类似香豆素的高效化学选择性分离;采用反相大内径AD-RH手性色谱柱,实现对映异构体的手性拆分;采用预测多反应监测模式,实现化学成分的高灵敏度检出;利用增强子离子扫描模式(EPI)采集各色谱峰的二级质谱信息,鉴定化学结构。通过定量离子对、定性离子对及两者的比值,判定是否为对映异构体。利用所构建的非手性-手性色谱耦联系统从毛前胡中共鉴定出60个化学成分,其中8对香豆素对映异构体得到了良好分离。本研究为毛前胡以及含有对映异构体中药的深入定性、定量分析提供可靠的方法。

Collection and identification of an unknown component from Eugenia uniflora essential oil exploiting a multidimensional preparative three-GC system employing apolar, mid-polar and ionic liquid stationary phases.

The present research deals with the collection and structural elucidation of an unknown component, accounting for about 35% of the essential oil obtained upon distillation of the leaves of Eugenia uniflora L., harvested during summer (January, 2017) in Paraná State (Southern Brazil). A multidimensional gas chromatographic preparative system, based on the coupling of three GC systems equipped with apolar, PEG and ionic liquid-based stationary phases, was successfully applied for the isolation of the chromatographic band relative to the unknown molecule. The use of wide-bore columns allowed for an increased sample capacity compared to conventional micro-bore columns, thus the injection of a neat sample was feasible, greatly reducing the total collection time. A higher chromatographic efficiency was afforded by the use of a multidimensional approach in the heart-cut mode, exploiting the different selectivity of three stationary phases, which ensured the attainment of a highly pure fraction. In only five runs, more than 3 milligrams were collected, with an average purity greater then 95%. Finally, the unknown component was subjected to nuclear magnetic resonance spectroscopy, mass spectrometry and condensed phase Fourier-transform infrared spectroscopy, leading to the identification of 6-ethenyl-6-methyl-3,5-di(prop-1-en-2-yl)cyclohex-2-en-1-one. The presented approach has been demonstrated to be effective for the isolation and structural elucidation of unknown molecules in complex samples, which will allow for further in-depth studies, like biological evaluation or pharmacological tests.

Temperature control in large-internal-diameter scaffolded monolithic columns operated at ultra-high pressures

Scaffolding makes it feasible to create organic-polymer monoliths in large confinements, such as wide-bore columns. By creating the scaffold from a metal good heat conductivity inside the column is obtained, which renders the relatively large columns (comparable with 4.6mm i.d.) suitable for application under ultra-high-pressure LC conditions. It was anticipated that the metal scaffold would allow accurate control of the temperature within the columns, but the temperature profiles within the columns could not be characterized using the previously available small-internal-diameter scaffolded columns. In the current study the internal diameter of the scaffolded columns was increased up to square conduits of 4×4mm. Prior to the formation of the stationary phase the heating efficiency in the empty scaffolded conduits was addressed. The performance of stationary phases created in the large scaffolds was investigated using the kinetic performance approach and the results were compared to those of the previous studies. Finally, scaffolded columns were tested under ultra-high-pressure LC conditions, where good temperature control is essential.

Titanium-scaffolded organic-monolithic stationary phases for ultra-high-pressure liquid chromatography

Organic-polymer monoliths with overall dimensions larger than one millimetre are prone to rupture – either within the monolith itself or between the monoliths and the containing wall – due to the inevitable shrinkage accompanying the formation of a cross-linked polymeric network. This problem has been addressed by creating titanium-scaffolded poly(styrene-co-divinylbenzene) (S-co-DVB) monoliths. Titanium-scaffolded monoliths were successfully used in liquid chromatography at very high pressures (up to 80MPa) and using gradients spanning the full range of water–acetonitrile compositions (0 to 100%). The kinetic-performance of (50-mm long) titanium-scaffolded monoliths was compared to that of similar monolith created in 1-mm i.d. glass-lined tubing at pressures up to 50MPa. The peak capacities obtained with the titanium-scaffolded column was about 30% lower. An increased Eddy-diffusion, due to the pillar-structure, and a decreased permeability are thought to be the main reasons for this reduced kinetic-performance. No decrease in performance was observed when the titanium-scaffolded columns were operated at pressures of 80MPa for up to 12h. The column-to-column repeatability (n=5) was acceptable in terms of observed peak widths at half heights (RSD ca. 10%) The run-to-run repeatability (n=135) in terms of retention times and peak widths at half height were found to be good. Titanium-scaffolded columns coupled in series up to a combined length of (200mm) were used for the analyses of a complex Escherichia coli protein sample. Our experiments demonstrate that columns based on titanium-scaffolded organic-polymer monolith can be operated under strenuous conditions without loss in performance. The titanium-scaffolded approach makes it feasible to create organic-polymer monoliths in wide-bore columns with accurate temperature control.

Quantification of Aqueous Monoethanolamine Concentration by Gas Chromatography for Postcombustion Capture of CO2

The availability of reliable analytical methods for measuring amine concentrations is necessary for optimum operation of aqueous amine CO2 separation systems being employed for postcombustion capture (PCC) of CO2. A GC-FID (gas chromatography with flame ionization detection) method is described for the reliable quantification of 30% (w/w) monoethanolamine (MEA) in severely degraded solvent samples. The observation of intermittent splitting of the MEA peak was a major concern with this approach. The use of a wide-bore column led to improved MEA peak resolution and peak shape. The reliability and robustness of the GC-FID method were assessed by analyzing degraded 30% (w/w) MEA solvent samples from CSIRO’s pilot plant at AGL’s Loy Yang power station in Victoria, Australia. The results were compared with those obtained by titration and total organic carbon (TOC) measurements of the same samples. The MEA concentrations obtained by the GC-FID and titration methods were statistically similar. In contrast, the MEA concentrations calculated from TOC were consistently higher than those obtained by both GC-FID and titration.

Rapid development of core–shell column technology: Accurate measurements of the intrinsic column efficiency of narrow-bore columns packed with 4.6 down to 1.3 μm superficially porous particles

The intrinsic heights equivalent to a theoretical plate (HETPs) of 31 narrow-bore and wide-bore columns packed with four different brands of core–shell particles were accurately measured on an optimized vHPLC instrument (1290 Infinity system) that has an extra-column volume variance of 13.6±0.3μL2. These results were derived from the slopes of the linear plots of the apparent plate heights of each column versus the reciprocal of (1+k′)2 for seven homologous compounds with a linear regression coefficient larger than 0.999. The results show that the kinetic performance of narrow-bore columns packed with core–shell particles increases almost linearly with decreasing particle diameter. The optimum reduced plate heights increase slightly from 1.6 to 1.9 with decreasing particle sizes from 4.6 to 1.3μm. This confirms that wide-bore columns provide better efficiencies than narrow-bore columns.

Comprehensive supercritical fluid chromatography × reversed phase liquid chromatography for the analysis of the fatty acids in fish oil

The separation of the phenacyl esters of the fatty acids originating from a fish oil extract by means of a comprehensive analysis using silver-ion (SI) supercritical fluid chromatography (SFC) and reversed phase liquid chromatography (RP-LC) in the first and second dimensions, respectively, is described. The combination ensured a high orthogonality and peak capacity, particularly when compared to the comprehensive RP-LC × 2RP-LC separation achieved by using a configuration with two columns in parallel in the second dimension. The construction of the SI-SFC × RP-LC interface consists of two two-position/ten-port switching valves, of which one is equipped with two loops packed with octadecyl silica (ODS) particles. Compared to the SFC × RP-LC configuration described in an earlier publication, the peak capacity in the second dimension was increased. Water was not only added as make-up fluid to the SFC effluent to ensure analyte focusing, but also as rinsing medium of the loops prior to the transfer of the fractions to the second dimension. In the SFC dimension, high efficiency and loadability were obtained by coupling two wide-bore columns (4.6 mm ID) in series. Evaporative light scattering (ELSD) and ultraviolet (UV) detection with standard and high-pressure flow cells were evaluated in terms of data acquisition speed and suppression of signal interferences originating from the supercritical carbon dioxide (CO 2) expansion.

Determination of Isosorbide Dinitrate in Serum by Gas Chromatography with New Generation of Electron Capture Detector and its Application in Pharmacokinetic Study

Isosorbide dinitrate (ISDN) is an effective drug in treatment of angina pectoris. In this study a new generation of electron capture detector (non-radioactive) with a short, non-polar and wide-bore column was used for analysis of ISDN in human serum. ISDN was extracted from serum by a mixture of ether and ethyl acetate and concentrated at room temperature. The method was linear between 5-50 ng/mL. Recovery and accuracy were 99-108% and greater than 90%, respectively, and inter-day precision was lower than 13%. Pharmacokinetic parameters were analyzed after oral administrations of Isocor 40 mg sustained release tablet in comparison with Isoket Retard 40. The statistical results obtained from comparison of C max , T max and AUC

Gas Chromatographic Determination of High Molecular Weight Alcohols from Policosanol in Omega-3 Fish Oil by Acylation with Acetyl Chloride

A new validated gas chromatographic (GC) method using acetyl chloride as a derivatizing agent for determining policosanol's high molecular weight alcohols (policosanol's fatty alcohols; PFAs) in fish oil (FO) is described. Before derivatizing the alcohols, FO was subjected to a methylation reaction, and then the PFAs were isolated in a chloroform fraction by silica gel by column liquid chromatography. GC analysis was performed using a BPX-5 wide-bore column and 1-eicosanol as an internal standard. Validation assays applied to the method proved noninterference by a very complex mixture of the FO with PFAs, even for samples subjected to stress conditions. Good linearity [correlation coefficient >0.999, relative standard deviation (RSD) of the slope <1.3%, and RSD of the response factors <1.9% with no bias] and accuracy (average recovery from 100.6 to 102.2%) over a range of 28-142% of the nominal concentration were obtained. Within-day and intermediate precisions at the nominal dose (100%) were 1.7 and 2.9%, respectively. The method was successfully used to identify and quantitate the PFAs in FO.

Turbulence as a Source of Excessive Baseline Noise during High-Speed Isocratic and Gradient Separations Using Absorption Detection

The occurrence of turbulent flow conditions in the connection tubing or at the entrance of the detection flow cell has been identified as a potential source of excessive detector noise in the signal of the diode array UV-absorption detector flow cell of a commercial HPLC system used to perform high-speed separations on wide-bore columns (4.6 mm i.d.). This excessive noise was found to occur abruptly if the flow rate is increased beyond a certain critical value or during gradient runs, if the mobile phase viscosity falls below a certain critical value. Several detector cells of different dimensions were studied to investigate the dependency of the effect on the detector cell design and the system tubing. Evidence for the turbulent flow origin of this noise is that its onset always occurred at a given fixed value of the Reynolds number. This critical Reynolds number could also be used to predict the onset of detector noise during gradient elution runs. Second, evidence for the turbulent flow origin of the noise was that it could be reliably eliminated using a flow splitter after the column to reduce the flow rate below its critical value before entering the detector. The loss in separation efficiency and detection sensitivity accompanying this flow splitting solution was found to be so small that it does not weigh up against the huge advantage of the possibility to eliminate the excessive detector noise.

Evaluation of five methods for derivatization and GC determination of a mixture of very long chain fatty acids (C 24:0–C 36:0)

D003 is a new active ingredient consisting of a mixture of very long chain saturated fatty acids (C 24:0–C 36:0) in a definite proportion, which shows antioxidant, antiosteoporotic, antiplatelet and cholesterol-lowering effects in experimental models. Five derivatization methods for determining these fatty acids by gas chromatography (GC), using diazomethane, sulphuric acid–methanol, hydrochloric acid–methanol, boron trifluoride–methanol and N-methyl- N-trimethylsilyltrifluoroacetamide were evaluated. GC analysis was carried out using a BPX-5 wide-bore column and 1-nonadecanoic acid (C 19:0) as internal standard. Methods were similar on account of the fatty acid content determined (84.2–86.6%). However, whereas the hydrochloric acid–methanol method needed 90 min to complete the derivatization, the other methods only required 10 min. Considering costs, speed, safety and GC response, the method using sulphuric acid–methanol was found the most appropriate for determining these fatty acids. The validation of this method: linearity over a range 40–160%, accuracy assessed through a recovery study, precision within day and inter-day, and specificity, even for samples subject to stress conditions, proved it is suitable for quality control and stability studies of the very long chain fatty acids composing this active ingredient.

Low-pressure gas chromatography–ion trap mass spectrometry for the fast determination of polycyclic aromatic hydrocarbons in air samples

A low-pressure gas chromatography–ion trap mass spectrometry (LPGC–ITMS) method was investigated to shorten the analysis time for 18 US Environmental Protection Agency priority listed polycyclic aromatic hydrocarbons (PAHs). Their elution was optimised with a short, wide-bore column coupled to a deactivated capillary at the inlet end and with a long, conventional column to compare their analytical performance. The analytical figures of merit under optimal LPGC–ITMS conditions were determined with respect to chromatographic separation, S/N ratio, limit of detection and precision. The peak width at half height of 1.5 s matched the ITMS duty cycle. Up to 16 PAHs in the molecular weight (MW) range of 128–278 Da could be separated in a very short time, i.e. less than 13 min using LPGC–ITMS, whereas with conventional GC–MS, it took approximately 40 min. However, LPGC–ITMS has a limited loss of separation power compared to that of conventional GC–MS due to the occurrence of three critical pairs for high-MW PAHs. For a practical evaluation, the LPGC–ITMS approach was applied to the determination of PAHs in gas and aerosol phase samples collected in the ambient air of Hasselt, Belgium.

Semipreparative-scale gas-chromatographic separation of filbertone enantiomers

The enantioselectivity of heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl-beta-CD) toward racemic filbertone (E-5-methyl-hep-2-en-4-one) was studied by performing the chiral separation on a capillary column, a thick-film wide-bore column and a semipreparative column. The semipreparative enantioseparation of filbertone was achieved at 80 degrees C by using a packed column providing (R)- and (S)-enantiomers of filbertone with ee 90 and 96%, respectively. The isolated enantiomers (approximately 250 microg each, ee = 90-96%) may be used for studies on the relationship of chirality and biological activity by olfactory screening and toxicological studies.

Validation of a gas chromatographic method for determining fatty acids that compose D003 in 10 mg film-coated tablets

D003 is a new product composed of a mixture of aliphatic fatty acids (C 24:0 to C 36:0), which shows antiplatelet, antithrombotic, antioxidant, and cholesterol-lowering effects in experimental models and human beings. A gas chromatographic method using a DB-5 wide-bore column and 1-nonadecanoic acid as internal standard was developed and validated in order to determine D003 in 10 mg film-coated tablets. The acids were analysed as methyl esters derivatives, prepared using 5% aqueous HCl-methanol. Developed method was specific for the active principle, even when samples were subjected to stress conditions. Good linearity (correlation coefficient > 0.99) and accuracy (total average recovery = 100.29%) were proven over a range 50–150% of the nominal concentration. Within-day and intermediate precisions at the nominal dose (100%) were < 1.5%. Robustness was examined through an intralaboratory study, quantification and resolution were only affected by the injection volume increase and no other of the 7 operational changes evaluated affected the results. The method was suitable for quality control and stability studies of these tablets.

Rapid determination of benzo( a)pyrene in olive oil samples with solid-phase extraction and low-pressure, wide-bore gas chromatography–mass spectrometry and fast liquid chromatography with fluorescence detection

Benzo( a)pyrene (B( a)P) was extracted from olive oil using solid-phase extraction on columns filled with Florisil and Nucleoprep C18. The extracts were analyzed with GC–MS, using standard capillary column and low-pressure wide-bore column (LP-GC–MS), as well as with HPLC on standard column and short donor–acceptor complex chromatography (DACC) column. Quantitation was done with isotope dilution method (GC–MS and LP-GC–MS) or with internal standard benzo( k)fluoranthene (HPLC). Limits of detection were 1 ng/g for GC–MS on standard column, 1.6 ng/g on LP-column, 0.5 ng/g for HPLC on standard column, and 0.3 ng/g on DACC column, respectively. The applied extraction method allowed handling over 50 samples per day and assured recovery over 80%. Matrix solid-phase dispersion, tried as an alternative isolation method, appeared less advantageous. Fast chromatographic methods (LP-GC–MS and HPLC on DACC) made it possible to reduce analysis time to 8 and 5 min, respectively. The method was applied to routine analysis of B( a)P in olive oil samples.

Gas chromatographic method for determining very long chain fatty acids that compose D003 in aqueous suspensions from 20 to 200 mg/ml, used in pharmacological and toxicological studies

D003 is a natural mixture of fatty acids (C 24:0 to C 36:0), which shows antiplatelet, antithrombotic, and cholesterol-lowering effects in experimental models. A specific gas chromatographic method, using a BPX-5 wide-bore column and 1-nonadecanoic acid as internal standard, was developed and validated to determine the content of D003 in 20–200 mg/ml aqueous suspensions, which are used in pharmacological and toxicological studies. Fatty acids were extracted with chloroform and converted to methyl esters derivatives using 5% aqueous HCl–methanol. The method was linear for suspensions ranging from 10 to 250 mg/ml (correlation coefficient=0.9998) and showed a good accuracy, with average recoveries (98.5–101.28%) no significantly different from 100%, according to the Student t-test ( P=0.05). The RSDs were <2.2%, indicating that the method has a good repeatability. The intermediate precision was good too, with RSDs between 1.20 and 2.10%. This method is suitable for quality control of these suspensions.