Identification of potent odourants in wine and brewed coffee using gas chromatography-olfactometry and comprehensive two-dimensional gas chromatography

Volatile constituents in wine and brewed coffee were analyzed using a combined system incorporating both GC-olfactometry (GC-O) and comprehensive two-dimensional GC-flame ionization detection (GC×GC-FID). A column set consisting of a 15m first dimension ((1)D; DB-FFAP (free fatty acid phase)), and a 1.0m (2)D column (DB-5 phase) was applied to achieve the GC×GC separation of the volatile extracts isolated by using solid phase extraction (SPE). While 1D GC resulted in many overlapping peaks, GC×GC allowed resolution of co-eluting compounds which coincided with the odour region located using GC-O. Character-impact odourants were tentatively identified through data correlation of GC×GC contour plots across results obtained using either time-of-flight mass spectrometry (TOFMS), or with flame photometric detection (FPD) for sulfur speciation. The odourants 2-methyl-2-butenal, 2-(methoxymethyl)-furan, dimethyl trisulfide, 2-ethyl-5-methyl-pyrazine, 2-octenal, 2-furancarboxaldehyde, 3-mercapto-3-methyl-1-butanol, 2-methoxy-3-(2-methylpropyl)-pyrazine, 2-furanmethanol and isovaleric acid were suspected to be particularly responsible for coffee aroma using this approach. The presented methodology was applied to identify the potent odourants in two different Australian wine varietals. 1-Octen-3-ol, butanoic acid and 2-methylbutanoic acid were detected in both Merlot and a Sauvignon Blanc+Semillon (SV) blend with high aroma potency. Several co-eluting peaks of ethyl 4-oxo-pentanoate, 3,7-dimethyl-1,5,7-octatrien-3-ol, (Z)-2-octen-1-ol, 5-hydroxy-2-methyl-1,3-dioxane were likely contributors to the Merlot wine aroma; while (Z)-3-hexen-1-ol, β-phenylethyl acetate, hexanoic acid and co-eluting peaks of 3-ethoxy-1-propanol and hexyl formate may contribute to SV wine aroma character. The volatile sulfur compound 2-mercapto-ethyl acetate was believed to contribute a fruity, brothy, meaty, sulfur odour to Australian Merlot and SV wines.     

Evaluation of ionic liquid stationary phases for one dimensional gas chromatography-mass spectrometry and comprehensive two dimensional gas chromatographic analyses of fatty acids in marine biota

Ionic liquid stationary phases were tested for one dimensional gas chromatography-mass spectrometry (GC-MS) and comprehensive two dimensional gas chromatography (GC×GC) of fatty acid methyl esters from algae. In comparison with polyethylene glycol and cyanopropyl substituted polar stationary phases, ionic liquid stationary phases SLB-IL 82 and SLB-IL 100 showed comparable resolution, but lower column bleeding with MS detection, resulting in better sensitivity. The selectivity and polarity of the ionic liquid phases are similar to a highly polar biscyanopropyl-silicone phase (e.g. HP-88). In GC×GC, using an apolar polydimethyl siloxane×polar ionic liquid column combination, an excellent group-type separation of fatty acids with different carbon numbers and number of unsaturations was obtained, providing information that is complementary to GC-MS identification.     

Comprehensive two-dimensional gas chromatography, retention indices and time-of-flight mass spectra of flavonoids and chalcones

The applicability of comprehensive two-dimensional gas chromatography (GC×GC) for flavonoids analysis was investigated by separation and identification of flavonoids in standards, and a complex matrix natural sample. The modulation temperature was optimized to achieve the best separation and signal enhancement. The separation pattern of trimethylsilyl (TMS) derivatives of flavonoids was compared on two complementary column sets. Whilst the BPX5/BPX50 (NP/P) column set offers better overall separation, BPX50/BPX5 (P/NP) provides better peak shape and sensitivity. Comparison of the identification power of GC×GC-TOFMS against both the NIST05 MS library and a laboratory (created in-house) TOFMS library was carried out on a flavonoid mixture. The basic retention index information on high-performance capillary columns with a non-polar stationary phase was established and database of mass spectra of trimethylsilyl derivatives of flavonoids was compiled. TOFMS coupled to GC×GC enabled satisfactory identification of flavonoids in complex matrix samples at their LOD over a range of 0.5-10 μg/mL. Detection of all compounds was based on full-scan mass spectra and for each compound a characteristic ion was chosen for further quantification. This study shows that GC×GC-TOFMS yields high specificity for flavonoids derived from real natural samples, dark chocolate, propolis, and chrysanthemum.     

Qualitative and quantitative analysis of pyrolysis oil by gas chromatography with flame ionization detection and comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry

Pyrolysis oils have attracted a lot of interest, as they are liquid energy carriers and general sources of chemicals. In this work, gas chromatography with flame ionization detector (GC-FID) and two-dimensional gas chromatography with time-of-flight mass spectrometry (GC×GC-TOFMS) techniques were used to provide both qualitative and quantitative results of the analysis of three different pyrolysis oils. The chromatographic methods and parameters were optimized and solvent choice and separation restrictions are discussed. Pyrolysis oil samples were diluted in suitable organic solvent and were analyzed by GC×GC-TOFMS. An average of 300 compounds were detected and identified in all three samples using the ChromaToF (Leco) software. The deconvoluted spectra were compared with the NIST software library for correct matching. Group type classification was performed by use of the ChromaToF software. The quantification of 11 selected compounds was performed by means of a multiple-point external calibration curve. Afterwards, the pyrolysis oils were extracted with water, and the aqueous phase was analyzed both by GC-FID and, after proper change of solvent, by GC×GC-TOFMS. As previously, the selected compounds were quantified by both techniques, by means of multiple point external calibration curves. The parameters of the calibration curves were calculated by weighted linear regression analysis. The limit of detection, limit of quantitation and linearity range for each standard compound with each method are presented. The potency of GC×GC-TOFMS for an efficient mapping of the pyrolysis oil is undisputable, and the possibility of using it for quantification as well has been demonstrated. On the other hand, the GC-FID analysis provides reliable results that allow for a rapid screening of the pyrolysis oil. To the best of our knowledge, very few papers have been reported with quantification attempts on pyrolysis oil samples using GC×GC-TOFMS most of which make use of the internal standard method. This work provides the ground for further analysis of pyrolysis oils of diverse sources for a rational design of both their production and utilization process.     

Fast gas chromatography with solid phase extraction clean-up for ultratrace analysis of pesticide residues in baby food

A sample preparation method based on single solvent phase extraction and solid-phase extraction (SPE-NH2) clean-up is studied in combination with fast capillary gas chromatography (GC) to determine 18 selected pesticides belonging to various chemical classes in apples, the common raw material for baby food production and baby food, at the concentration level < or = 10 microg/kg maximum residual limit (MRL). Possibilities of mass spectrometry (MS) detector and electron capture detector (ECD) in fast gas chromatography (GC) of samples with complex matrice at ultra trace levels of pesticide residues were studied and compared. MS detection in single ion monitoring (SIM) mode provided higher selectivity compared to ECD. Optimisation of extraction as well as the simplifying of the whole process of sample preparation was carried out. Recoveries obtained at concentration level of 5 microg/kg (the required value for limit of quantification (LOQ) in baby food) were >90%, except of dimethoate (77.7%) and captan (46.4%) with MS detection. The obtained LOQs were at least 1 order lower than 5 microg/kg for the majority of compounds. The repeatability of gas chromatography-mass spectrometry (GC-MS) measurements of the matrix matched standards expressed as relative standard deviation was <11% except of captan and cypermethrin.     

Identification of volatiles from pineapple (Ananas comosus L.) pulp by comprehensive two-dimensional gas chromatography and gas chromatography/mass spectrometry

Combining qualitative data from the chromatographic structure of 2-D gas chromatography with flame ionization detection (GC×GC-FID) and that from gas chromatography-mass spectrometry (GC/MS) should result in a more accurate assignment of the peak identities than the simple analysis by GC/MS, where coelution of analytes is unavoidable in highly complex samples (rendering spectra unsuitable for qualitative purposes) or for compounds in very low concentrations. Using data from GC×GC-FID combined with GC/MS can reveal coelutions that were not detected by mass spectra deconvolution software. In addition, some compounds can be identified according to the structure of the GC×GC-FID chromatogram. In this article, the volatile fractions of fresh and dehydrated pineapple pulp were evaluated. The extraction of the volatiles was performed by dynamic headspace extraction coupled to solid-phase microextraction (DHS-SPME), a technique appropriate for slurries or solid matrices. Extracted analytes were then analyzed by GC×GC-FID and GC/MS. The results obtained using both techniques were combined to improve compound identifications.     

Fast sample preparation involving MASE and coupled column normal phase liquid chromatography for the rapid trace analysis of dioxins in air-dust samples from fire catastrophe emissions

A new approach has been developed and tested for the urgent analysis of dioxins in samples of air-dust filters originating from catastrophe emissions. The procedure consists of a fast extraction of the sample with microwave solvent extraction (MASE) and acetone as solvent followed by a fast cleanup of the extract with normal phase coupled column liquid chromatography (LC/LC).

The multi-dimensional LC/LC system employs a 50 mm×4.6 mm i.d. column packed with 3 μm silica and a 150 mm×4.6 mm i.d. column packed with 5 μm PYE as the first and second analytical column, respectively. Iso-hexane is used on both columns to perform cleanup and dichloromethane to perform efficient back-flush elution of the compounds from the second column. The obtained polarity-based separation in the first dimension and molecular-structure based separation in the second dimension provides a fast and powerful cleanup.

Validation was done by analysing samples of homemade RIVM air-dust with aged residues (n=8, spiking level about 15 pg mg⁻¹ per compound) of dioxins/furans and samples of reference Urban Dust SRM 1649a (n=4) with both the new approach and the existing conventional procedure and were instrumentally analyzed with capillary gas chromatography and high resolution mass spectrometric detection (GC/HRMS).

In comparison to the existing conventional procedure, the new approach reduces sample processing from several days to several hours per sample.

As regards the aged-residue air-dust samples, the new method shows a good accuracy, precision and high selectivity providing a performance in good agreement with the existing procedure. In SRM air-dust, the concentration of a few compounds obtained by the new method was below (10–50%) the certified value.     

On retentivity tuning by flow in the second column of different comprehensive two dimensional gas chromatographic configurations

Retentivity tuning in comprehensive two dimensional GC separations of aliphatics (linear and cyclic hydrocarbons) and aromatics in gasoline by changing the carrier gas flows in the column series at constant working temperature parameters of both columns is discussed. Comprehensive 2D techniques studied include GC×GC with cryogenic and differential flow modulation and non-modulated transfer (NMT). In all configurations, the first dimension was a non-polar column and the second dimension a polar column. Using three different flows (0.6, 1.0 and 1.4mL/min) of helium carrier gas in cryogenic modulated GC×GC illustrated that, as expected, retention of the solutes on the (1)D and (2)D columns increased but the separation quality was nearly constant. A change of carrier gas pressure (p(m)=175-125kPa) on the (1)D and (2)D columns joint point at constant inlet pressure (p(i)=525kPa) in NMT, induces an increase of the carrier gas flow rate on the (1)D and a decrease on the (2)D column, respectively. The higher retentivity of the (2)D column improved the group type separation of aliphatic/cyclic hydrocarbons and aromatics and a higher distribution of aromatics on the 2D retention plane was noted. Retentivity tuning was also performed in flow modulated GC×GC by operating the (1)D column at 0.8mL/min and the (2)D column at 20 and 26mL/min. The higher retentivity at 20mL/min improved the group type separation of aliphatic/cyclic hydrocarbons and aromatics in the 2D retention plane.     

Stir bar sorptive extraction and comprehensive two-dimensional gas chromatography coupled to high-resolution time-of-flight mass spectrometry for ultra-trace analysis of organochlorine pesticides in river water

A method for the determination of ultra-trace amounts of organochlorine pesticides (OCPs) in river water was developed by using stir bar sorptive extraction (SBSE) followed by thermal desorption and comprehensive two-dimensional gas chromatography coupled to high-resolution time-of-flight mass spectrometry (SBSE-TD-GC×GC-HRTOF-MS). SBSE conditions such as extraction time profiles, phase ratio (β: sample volume/polydimethylsiloxane (PDMS) volume), and modifier addition, were examined. Fifty milli-liter sample including 10% acetone was extracted for 3 h using stir bars with a length of 20 mm and coated with a 0.5 mm layer of PDMS (PDMS volume, 47 μL). The stir bar was thermally desorbed and subsequently analyzed by GC×GC-HRTOF-MS. The method showed good linearity over the concentration range from 50 to 1000 pg L(-1) or 2000 pg L(-1) for all analytes, and the correlation coefficients (r(2)) were greater than 0.9903 (except for β-HCH, r(2)=0.9870). The limit of detection (LOD) ranged from 10 to 44 pg L(-1). The method was successfully applied to the determination of 16 OCPs at pg L(-1) to ng L(-1) in river water. The results agree fairly well with the values obtained by a conventional liquid-liquid extraction (LLE)-GC-HRMS (selected ion monitoring: SIM) method using large sample volume (20 L). The method also allows screening of non-target compounds, e.g. pesticides and their degradation products, polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and pharmaceuticals and personal care products (PPCPs) and metabolites in the same river water sample, by using full spectrum acquisition with accurate mass in GC×GC.     

SPME-GC联用测定环境水样中的酚类化合物

建立了固相微萃取与气相色谱联用技术测定环境水样中酚类化合物的方法. 探讨了pH、离子强度、萃取头类型、萃取时间以及解析时间等条件对酚类化合物萃取量的影响, 优化了GC仪器条件. 在优化的条件下, 酚类化合物的响应值与浓度有良好的线性关系, 线性范围为0.20～200 μg/L, 检出限在0.019～0.10 μg/L之间, 相对标准偏差(RSD, n=5)为4.4%～11%, 水样平均加标回收率为92.2%～101.9%, 所建立的方法可测定环境水样中的酚类化合物.     

Determination of underivatised efaroxan and idazoxan in blood plasma by capillary gas chromatography with mass-selective detection

Sensitive and specific methods for the determination of efaroxan and idazoxan in blood plasma have been developed based on solvent extraction, chromatographic separation and quantification by selected-ion monitoring using a quadruple mass-selective detector. The use of a short non-polar bonded-phase capillary gas chromatography (GC) column facilitated rapid separation of the compounds of interest from internal standards, metabolites and endogenous material. Of equal significance was the ability to chromatograph these basic compounds without prior derivatisation. The application of bonded-phase capillary GC coupled to selected-ion monitoring resulted in robust analytical procedures with sub-ng ml(-1) sensitivity and high selectivity.     

Optimization of comprehensive two dimensional gas chromatography-flame ionization detection-quadrupole mass spectrometry for the separation of octyl- and nonylphenol isomers

In the present work, the separation of complex nonylphenol technical mixtures has been optimized using comprehensive two-dimensional gas chromatography coupled with a flame ionization detector and quadrupole mass spectrometer (GC×GC-qMS), using valve-based modulator. The optimization of GC×GC-qMS has been carried out using experimental designs and the optimal separation was obtained at the following conditions: 1st column flow: 1mL/min; 2nd column flow: 17.75 mL/min, oven temperature ramp: 1°C/min, modulation period: 1.5s and discharge time: 0.12s. These values have been used to determinate the previously synthesized 22OP, 33OP, 363NP and 22NP isomers in two different nonylphenol technical mixtures. Percentages obtained were as follows: 4.86% and 0.59% for 22OP, 4.91% and 2.82% for 33OP, 11.79% and 7.71% for 363NP and 2.28% and 1.98% for 22NP, in Fluka and Aldrich mixtures, respectively. The values obtained for NP isomers are in good agreement with the literature.     

High-speed gas chromatography: an overview of various concepts.

An overview is given of existing methods to minimise the analysis time in gas chromatography (GC) being the subject of many publications in the scientific literature. Packed and (multi-) capillary columns are compared with respect to their deployment in fast GC. It is assumed that the contribution of the stationary phase to peak broadening can be neglected (low liquid phase loading and thin film columns, respectively). The treatment is based on the minimisation of the analysis time required on both column types for the resolution of a critical pair of solutes (resolution normalised conditions). Theoretical relationships are given, describing analysis time and the related pressure drop. The equations are expressed in reduced parameters, making a comparison of column types considerably simpler than with the conventional equations. Reduction of the characteristic diameter, being the inside column diameter for open tubular columns and the particle size for packed columns, is the best approach to increase the separation speed in gas chromatography. Extremely fast analysis is only possible when the required number of plates to separate a critical pair of solutes is relatively low. Reducing the analysis time by reduction of the characteristic diameter is accompanied by a proportionally higher required inlet pressure. Due to the high resistance of flow of packed columns this seriously limits the use of packed columns for fast GC. For fast GC hydrogen has to be used as carrier gas and in some situations vacuum-outlet operation of capillary columns allows a further minimisation of the analysis time. For fast GC the columns should be operated near the conditions for minimum plate height. Linear temperature programmed fast GC requires high column temperature programming rates. Reduction of the characteristic diameter affects the sample capacity of the "fast columns". This effect is very pronounced for narrow-bore columns and in principle non-existing in packed columns. Multi-capillary columns (a parallel configuration of some 900 narrow-bore capillaries) take an intermediate position.     

Supercritical fluid extraction of vapor-deposited pyrene from carbonaceous coal stack ash

The efficiencies of extraction of vapor-deposited pyrene from a high-carbon coal stack ash by Soxhlet extraction with methanol, ultrasonic extraction with toluene, acid pretreatment and subsequent ultrasonic extraction with toluene, batch extraction with toluene, and supercritical fluid extraction (SFE) are compared. SFE using CO(2) or isobutane yielded extraction recoveries virtually identical with those obtained using ultrasonic or Soxhlet extraction processes. Collection of the SFE extract was performed by expansion into a solvent or onto the head of a gas chromatography (GC) column. No loss of extracted pyrene was observed upon collection of methanol-modified CO(2) SFE by expansion into methanol. Also, no loss of pure CO(2) SFE extract was observed upon collection on the head of a GC column. However, use of a methanol or toluene modifier for CO(2) SFE directly coupled to GC effected complete loss of extracted pyrene.     

顶空固相微萃取-气相色谱-质谱法测定玩具中可迁移有机锡化合物

建立了顶空固相微萃取结合气相色谱-质谱联用技术测定玩具中10种可迁移有机锡化合物的方法。玩具材料经0.07 mol/L HCl浸泡2 h后,使用醋酸-醋酸钠缓冲溶液将浸泡液的pH值调至4.7,然后加入四乙基硼化钠将浸泡液中的有机锡化合物乙基化,在振荡条件下用100 μ m聚二甲基硅氧烷(PDMS)纤维进行顶空固相微萃取,萃取完成后将纤维插入气相色谱进样口进行热解吸,使用DB-5毛细管柱对10种有机锡化合物进行分离。10种有机锡化合物的检出限为0.5~5 μg/kg。两个加标水平(0.500 μg/L和5.00 μg/L)下的回收率分别为80.7%~118.7%和86.2%~120.5%,RSD均低于15%。应用该方法测定了玩具可触及材料(包括涂层、织物、塑料、木料)中的可迁移有机锡化合物。该方法简便、快速、灵敏度高,不需使用有毒有机溶剂,绿色环保。     

A flexible loop-type flow modulator for comprehensive two-dimensional gas chromatography

The present investigation is focused on a simple flow modulator (FM), for comprehensive two-dimensional gas chromatography (GC×GC). The interface is stable at high temperatures, and consists of a metallic disc (located inside the GC oven) with seven ports, which are connected to an auxiliary pressure source via two branches, to the first and second dimension, to a waste branch (linked to a needle valve) and to an exchangeable modulation loop (2 ports). The ports are connected via micro-channels, etched on one of the inner surfaces of the disc. Modulation is achieved using a two-way electrovalve, connected on one side to the additional pressure source, and to the two metal branches, on the other. An FM enantio-GC×polar-GC method (using a flame ionization detector) was optimized (a 40-μL loop was employed), for the analysis of essential oils. As an example, an application on spearmint oil is shown; the method herein proposed was subjected to validation. Finally, an FM GC×GC diesel experiment was carried out, using an apolar-polar column combination, to demonstrate the effectiveness of the modulator in the analysis of a totally different sample-type.     

Establishing an alternative method for the quantitative analysis of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans by comprehensive two dimensional gas chromatography-time-of-flight mass spectrometry for developing countries

Comprehensive Gas Chromatography-Time-of-Flight Mass Spectrometry (GC×GC-TOFMS) methodology has been refined for the analysis of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in samples with different matrices. This is specifically for application in developing countries where access to gas chromatography-high resolution mass spectrometry (GC-HRMS) and highly skilled personnel is limited. The method, using an Rxi-5 Sil MS column in the first dimension ((1)D) coupled with an Rtx-200 column in the second dimension ((2)D), was used to quantify PCDDs and PCDFs in different environmental sample matrices. The results were compared with those obtained using GC-HRMS and good agreement was observed. The limit of detection (LOD) for the method (300fg on column for spiked soil samples) was determined using an Rxi-XLB ((1)D) column coupled with an Rtx-200 column ((2)D). Preliminary South African sample results are also discussed. Isomer specificity for different tetrachloro dibenzo-p-dioxins (TCDDs) and tetrachloro dibenzofurans (TCDFs) was investigated using a commercial standard. Adequate resolution was achieved. The method as described has great attraction for developing countries being both financially and operationally favourable.     

Achieving high peak capacity production for gas chromatography and comprehensive two-dimensional gas chromatography by minimizing off-column peak broadening

By taking into consideration band broadening theory and using those results to select experimental conditions, and also by reducing the injection pulse width, peak capacity production (i.e., peak capacity per separation time) is substantially improved for one dimensional (1D-GC) and comprehensive two dimensional (GC×GC) gas chromatography. A theoretical framework for determining the optimal linear gas velocity (the linear gas velocity producing the minimum H), from experimental parameters provides an in-depth understanding of the potential for GC separations in the absence of extra-column band broadening. The extra-column band broadening is referred to herein as off-column band broadening since it is additional band broadening not due to the on-column separation processes. The theory provides the basis to experimentally evaluate and improve temperature programmed 1D-GC separations, but in order to do so with a commercial 1D-GC instrument platform, off-column band broadening from injection and detection needed to be significantly reduced. Specifically for injection, a resistively heated transfer line is coupled to a high-speed diaphragm valve to provide a suitable injection pulse width (referred to herein as modified injection). Additionally, flame ionization detection (FID) was modified to provide a data collection rate of 5kHz. The use of long, relatively narrow open tubular capillary columns and a 40°C/min programming rate were explored for 1D-GC, specifically a 40m, 180μm i.d. capillary column operated at or above the optimal average linear gas velocity. Injection using standard auto-injection with a 1:400 split resulted in an average peak width of ～1.5s, hence a peak capacity production of 40peaks/min. In contrast, use of modified injection produced ～500ms peak widths for 1D-GC, i.e., a peak capacity production of 120peaks/min (a 3-fold improvement over standard auto-injection). Implementation of modified injection resulted in retention time, peak width, peak height, and peak area average RSD%'s of 0.006, 0.8, 3.4, and 4.0%, respectively. Modified injection onto the first column of a GC×GC coupled with another high-speed valve injection onto the second column produced an instrument with high peak capacity production (500-800peaks/min), ～5-fold to 8-fold higher than typically reported for GC×GC.     

Two‐phase electromembrane extraction followed by gas chromatography‐mass spectrometry analysis

A two‐phase electromembrane extraction (EME) was developed and directly coupled with gas chromatography mass spectrometry (GC‐MS) analysis. The proposed method was successfully applied to the simultaneous determination of imipramine, desipramine, citalopram and sertraline. The model compounds were extracted from neutral aqueous sample solutions into the organic phase filled in the lumen of the hollow fiber. This method was accomplished with 1‐heptanol as organic phase, by means of 60 V applied voltage and with the extraction time of 15 min. Experiments reported recoveries in the range of 69–87% from 1.2 mL neutral sample solution. The compounds were quantified by GC‐MS instrument, with acceptable linearity ranging from 1 to 500 ng mL^?1 (R² in the range of 0.989 to 0.998), and repeatability (RSD) ranging between 7.5 and 11.5% (n = 5). The estimated detection limits (S/N ratio of 3:1) were less than 0.25 ng mL^?1. This novel approach based on two‐phase EME brought advantages such as simplicity, low‐costing, low detection limit and fast extraction with a total analysis time less than 25 min. These experimental findings were highly interesting and demonstrated the possibility of solving ionic species in the organic phase at the presence of electrical potential.     

Comprehensive two-dimensional gas chromatography for the analysis of synthetic and crude-derived jet fuels

Fully synthetic jet fuel (FSJF) produced via Fischer-Tropsch (FT) technology was recently approved by the international aviation fuel authorities. To receive approval, comparison of FSJF and crude-derived fuel and blends on their qualitative and quantitative hydrocarbon composition was of utmost importance. This was performed by comprehensive two-dimensional gas chromatography (GC×GC) in the reversed phase mode. The hydrocarbon composition of synthetic and crude-derived jet fuels is very similar and all compounds detected in the synthetic product are also present in crude-derived fuels. Quantitatively, the synthetic fuel consists of a higher degree of aliphatic branching with less than half the aromatic content of the crude-derived fuel. GC×GC analyses also indicated the presence of trace levels of hetero-atomic impurities in the crude-derived product that were absent in the synthetic product. While clay-treatment removed some of the impurities and improved the fuel stability, the crude-derived product still contained traces of cyclic and aromatic S-containing compounds afterwards. Lower level of aromatics and the absence of sulphur are some of the factors that contribute to the better fuel stability and environmental properties of the synthetic fuel. GC×GC was further applied for the analysis of products during Jet Fuel Thermal Oxidation Testing (JFTOT), which measures deposit formation of a fuel under simulated engine conditions. JFTOT showed the synthetic fuel to be much more stable than the crude-derived fuel.