Non-polar Column Research Articles

Comprehensive two-dimensional gas chromatography for enhanced analysis of naphthas: New column combination involving permethylated cyclodextrin in the second dimension

A new column association using comprehensive two-dimensional gas chromatography for the detailed molecular analysis of hydrocarbon mixtures is reported in this paper. In order to compare the impact of two different secondary columns, a novel column combination relying on a GC × 2GC system was used. This system is based on a non-polar first column (PONA) combined with both a permethylated β-cyclodextrin (β-Dex 120) stationary phase and a polysilphenylensiloxane (BPX 50) in the second dimension. Compared to BPX 50 stationary phase, the implementation of β-cyclodextrin columns as the second dimension was found to improve the resolution between paraffins and naphthenes in the naphtha range but not in the middle distillate range. Attempts to improve the results and to understand the interaction mechanism remained unsuccessful. Therefore, the benefits of the β-Dex 120-column are only demonstrated on heavy naphtha cut for the quantitation of hydrocarbons.

Direct Method of Preparation of Dodecanesulfonamide Derivatives and Some Surface Properties

AbstractAlkanesulfonamide compounds are known as surfactants because of the presence of –SO2NH– function in their molecule. Thus, they are used in many formulations in the chemical and textile industries and also as inhibitors of corrosion. Generally, sulfonamide derivatives are prepared using sulfonyl chlorides as the raw material. The methods often described in the literature involve the use of ammonia gas and pressure. A simple and direct method to prepare pure alkanesulfonamide derivatives possessing good surface properties is presented in this work. Thus, n‐dodecanesulfonyl chlorides obtained by photochemical sulfochlorination of n‐dodecane under visible light using sulfuryl chloride were separated from the reaction mixture. These sulfonyl chlorides, a mixture of primary and secondary isomers, were transformed in one step into N‐ethyldodecanesulfonamides, N‐ethanoldodecanesulfonamides and the salts of dodecanesulfonamidoacetic acid. After purification on chromatographic column, the six position isomers of these sulphonamide derivatives were analysed and well separated by gas phase chromatography using a nonpolar column. Then, gas phase chromatography analysis coupled to mass spectrometry using electronic impact (GC/MS/IE) was performed to identify the different position isomers. The primary isomers of sulphonamide derivatives were identified by crossed injection of the compounds obtained by synthesis from the 1‐chlorododecane using the Grignard reagent, and identified by IR,1H‐ and 13C‐RMN, elementary analysis and GC/MS/IE. Some physico‐chemical properties of these sulphonamide derivatives were examined. The variation of surface tension versus the concentration of both primary and secondary sulphonamide derivatives were studied, and the critical micellar concentration was determined for the compounds showing surface activity. The foaming power was also determined by the Bartsch method, and the results obtained were compared to those of a commercial surfactant, the linear alkylbenzenesulfonate. The stability of the foam formed was also evaluated.

Comprehensive two-dimensional GC (GC × GC) qMS analysis of tetrachloronaphthalenes in Halowax formulations

A combination of non-polar and shape selective columns in a comprehensive two-dimensional GC (GC × GC) system consisting of DB-5MS and LC-50 as the 1st and 2nd dimension columns was used to separate 22 tetrachloronaphthalene isomers. These columns enabled separation of all possible isomers of tetraCN found in the technical chloronaphthalene Halowax formulations into 18 peaks covering 15 single separated isomers and 7 co-eluting in triplicate (1,2,4,6-/1,2,4,7-/1,2,5,7-tetraCN; nos. 33/34/37) and in pairs (1,2,3,7-/1,2,4,5-tetraCN; nos. 30/32 as well as 1,3,5,8-/1,3,6,8-tetraCN; nos. 43/45). Twelve isomers of tetraCN resolved as single compounds by the GC x GC system used were found in Halowax 1001, 1013, 1014 and 1099 as well as in Equi-Halowax mixture. Three other tetraCNs that could be also resolved as single compounds were not detected in these materials, while the remaining 7 tetraCNs, which co-eluted, waits a further separation. The majority of constituents of the tetraCN homologue group of the Halowax formulations are isomers such as 1,4,5,8- (no. 46), 1,2,5,8- (no. 38), 1,2,4,8-tetraCN (no. 35), co-eluting 1,3,5,8-tetraCN (no. 43 in a pair nos. 43/45) and also co-eluting 1,2,4,6-/1,2,4,7-/1,2,5,7-tetraCN (nos. 33/34/37). The less abundant by amongst of tetraCNs in these mixtures are 1,4,6,7- (no. 47) and 1,3,5,7-tetraCN (no. 42). The remaining seven isomers, i.e., 1,2,3,4- (no. 27), 1,2,3,5- (no. 28), 1,2,3,6- (no. 29), 1,2,5,6- (no. 36), 1,2,6,7- (no. 39), 1,2,6,8- (no. 40) and 1,2,7,8-tetraCN (no. 41) are usually minor by quantity, while 1,2,3,7-/1,2,4,5-tetraCN (nos. 30/32) are also minor, or one of them is absent. Three tetraCNs not found in the Halowax formulations are isomers such as 1,2,3,8-tetraCN (no. 31), 1,3,6,7-tetraCN (no. 44) and 2,3,6,7-tetraCN (no. 48).

Estimation of Kovats Retention Indices Using Group Contributions.

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Simple and sensitive method for determination of nitrated polycyclic aromatic hydrocarbons in diesel exhaust particles by gas chromatography-negative ion chemical ionisation tandem mass spectrometry

An extremely simple and sensitive method was developed for determination of nitrated polycyclic aromatic hydrocarbons (nitro-PAHs; mono-nitro-PAHs and dinitropyrenes) in diesel exhaust particles (DEPs) by gas chromatography-negative ion chemical ionisation tandem mass spectrometry (GC/NCI/MS/MS). We used two types of column in GC/NCI/MS/MS analysis. A polar column was used for determination of mono-nitro-PAHs, and a non-polar column was used for determination of dinitropyrenes and mono-nitro-PAHs except nitrofluoranthenes. The proposed method requires no clean-up procedure. The limits of detection ranged from 0.01 to 0.09 pg for all compounds tested. The applicability of the method to DEP samples was validated using diesel particulate standard reference materials (SRMs). Although DEPs contain complex matrices, all compounds could be detected easily in SRM2975 (diesel particulate matter) and SRM1975 (diesel particulate extract) without a clean-up procedure. The RSDs were less than 5% for all compounds examined. The quantitative results for SRMs exhibited good agreement with the available data in the literature. These results indicate that the proposed GC/NCI/MS/MS method is useful for determination of nitro-PAHs in DEP samples.

Quantitative structure‐activity relationship modeling on in vitro endocrine effects and metabolic stability involving 26 selected brominated flame retardants

In this work, quantitative structure-activity relationships (QSARs) were developed to aid human and environmental risk assessment processes for brominated flame retardants (BFRs). Brominated flame retardants, such as the high-production-volume chemicals polybrominated diphenyl ethers (PBDEs), tetrabromobisphenol A, and hexabromocyclododecane, have been identified as potential endocrine disruptors. Quantitative structure-activity relationship models were built based on the in vitro potencies of 26 selected BFRs. The in vitro assays included interactions with, for example, androgen, progesterone, estrogen, and dioxin (aryl hydrocarbon) receptor, plus competition with thyroxine for its plasma carrier protein (transthyretin), inhibition of estradiol sulfation via sulfotransferase, and finally, rate of metabolization. The QSAR modeling, a number of physicochemical parameters were calculated describing the electronic, lipophilic, and structural characteristics of the molecules. These include frontier molecular orbitals, molecular charges, polarities, log octanol/water partitioning coefficient, and two- and three-dimensional molecularproperties. Experimental properties were included and measured for PBDEs, such as their individual ultraviolet spectra (200-320 nm) and retention times on three different high-performance liquid chromatography columns and one nonpolar gas chromatography column. Quantitative structure-activity relationship models based on androgen antagonism and metabolic degradation rates generally gave similar results, suggesting that lower-brominated PBDEs with bromine substitutions in ortho positions and bromine-free meta- and para positions had the highest potencies and metabolic degradation rates. Predictions made for the constituents of the technical flame retardant Bromkal 70-5DE found BDE 17 to be a potent androgen antagonist and BDE 66, which is a relevant PBDE in environmental samples, to be only a weak antagonist.

Estimation of Kováts Retention Indices Using Group Contributions

We have constructed a group contribution method for estimating Kováts retention indices by using observed data from a set of diverse organic compounds. Our database contains observed retention indices for over 35,000 different molecules. These were measured on capillary or packed columns with polar and nonpolar (or slightly polar) stationary phases under isothermal or nonisothermal conditions. We neglected any dependence of index values on these factors by averaging observations. Using 84 groups, we determined two sets of increment values, one for nonpolar and the other for polar column data. For nonpolar column data, the median absolute prediction error was 46 (3.2%). For data on polar columns, the median absolute error was 65 (3.9%). While accuracy is insufficient for identification based solely on retention, it is suitable for the rejection of certain classes of false identifications made by gas chromatography/mass spectrometry.

Advanced Gas Chromatographic–Mass Spectrometric Studies for Identification of the Cellular Octadecenoate Isomers and Changes of Fatty Acid Composition Induced by Ethanol Stress in Escherichia coli and Escherichia coli O157:H7

Ethanol can be introduced to foods of various origins and is commonly used for surface disinfection. Low concentrations of residual ethanol may provide an opportunity for pathogens to adapt and grow. Change of cellular fatty acid composition is one of adaptation mechanisms enabling bacteria to grow under varied stresses. Since instrumental analyses of bacterial octadecenoate isomers are sophisticated, gas chromatographic analyses of the isomers, namely trans-9-octadecenoate, trans-11-octadecenoate, cis-9-octadecenoate, and cis-11-octadecenoate, and ethanol-induced formation of trans-9-octadecenoate in Escherichia coli and E. coli O157:H7 were intensively investigated. When an HP-1, a nonpolar capillary column, was used for gas chromatographic analyses of 28 authentic bacterial acid methyl esters, resolution was satisfied for all fatty acid components except trans-9-octadecenoate and cis-11-octadecenoate, being overlapped. When the column was replaced by an RTx-2330, a polar capillary column, all of the above-mentioned octadecenoate isomers were resolved. When cells of E. coli and E. coli O157:H7 were harvested after submerged cultivation (30°C, 150 rpm) in tryptic soy broth and tryptic soy broth supplemented with 5% ethanol at early stationary phase and subjected to cellular fatty acid analyses by using an HP-1 and RTx-2330 coupled with a mass detector, 12 fatty acids, i.e., trans-9-octadecenoate, 5 saturated fatty acids, 2 cyclopropane fatty acids and 4 cisunsaturated fatty acids, were identified. Individual fatty acid contents varied depending on nature of fatty acid, strain of E. coli, and supplement of ethanol. As affected by ethanol stress for both E. coli strains, contents of trans-9-octadecenoate increased, whereas contents of cyc-9,10-methylene octadecanoate (cyc-9,10-19:0) decreased significantly (P < 0.05). Apparently, both E. coli strains have rendered necessary fatty acid adaptation to survive and grow under ethanol stress.

Inter‐laboratory comparison of elemental analysis and gas chromatography combustion isotope ratio mass spectrometry (GC‐C‐IRMS). Part I: δ13C measurements of selected compounds for the development of an isotopic Grob‐test

This study was directed towards investigating suitable compounds to be used as stable isotope reference materials for gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS) calibration. Several compounds were selected from those used in the 'Grob-test' mixture. Oxygen- and nitrogen-containing substances were added to these compounds to allow the mixture to be used as a possible multi-isotopic calibration tool for 2H/1H, 13C/12C, 15N/14N and 18O/16O ratio determinations. In this paper we present the results of delta13C measurements performed by the consortium of the five laboratories taking part in this inter-calibration exercise. All the compounds were individually assessed for homogeneity, short-term stability and long-term stability by means of EA-IRMS, as required by the bureau communitaire de reference (BCR) Guide for Production of Certified Reference Materials. The results were compared then with the GC-C-IRMS measurements using both polar and non-polar columns, and the final mixture of selected compounds underwent a further certification exercise assessing limits of accuracy and reproducibility under specified GC-C-IRMS conditions.

Monitoring of multi-class pesticide residues in fresh grape samples using liquid chromatography with electrospray tandem mass spectrometry

A sensitive and selective liquid chromatography–electrospray ionization–tandem mass spectrometry (LC–ESI–MS–MS) method was developed for the routine analysis of 10 multi-class pesticides residues (imidacloprid, thiamethoxam, chlorpyrifos, dimethoate, monocrotophos, metalaxyl, methomyl, hexaconazole, myclobutanil, carbendazim) in fresh grape samples. A miniaturized extraction-partition procedure that requires small amounts of non-chlorinated solvents was used. The extracts were analyzed by LC–ESI–MS–MS without any further cleanup step. The pesticides are separated on a reversed phase non-polar column using a gradient elution. Mean recoveries obtained at fortification levels of 0.010–0.100 mg/kg were 78–104% for all compounds, with relative standard deviations (RSDs) of ⩽15%. The LC–MS–MS method allowed sensitive and selective quantification and identification at low levels in different matrices. The method was applied for analysis of fresh grape samples collected from an agricultural area in Hyderabad, South India. The results revealed that the concentrations of studied pesticide residues in grape samples were in the permissible limits except monocrotophos.

Contribution of thermal desorption and liquid–liquid extraction for identification and profiling of impurities in methamphetamine by gas chromatography–mass spectrometry

Impurity profiling of methamphetamine (MA) using thermal desorption (TD) and gas chromatography–mass spectrometry (GC–MS) was examined. Using TD/GC–MS, impurities were extracted and separated under various conditions. Optimal chromatograms were obtained when a 20 mg MA sample was extracted at 120 °C for 3 min using a TD instrument, followed by separation of the extracts using a non-polar capillary column coated with (5%phenyl)-methylpolysiloxane. MA samples from nine different batches were analyzed under optimized conditions. Compounds related to the structure of MA, such as benzaldehyde, benzyl alcohol, amphetamine, cis- and trans-1,2-dimethyl-3-phenylaziridine, dimethylamphetamine, and N-acetylephedrine, were detected in the chromatograms without any laborious extraction procedure. Compounds such as ethanol, diethyl ether, and acetic acid, which are considered reagents and solvents for MA synthesis, were also detected in some of the chromatograms. The numbers and intensities of the peaks detected were different among the samples. Impurity profiling of MA using TD was compared with that using liquid–liquid extraction (LLE). Better reproducibility of peak areas was obtained using LLE, whereas higher intensities and numbers of peaks were detected using TD. Solvents were extracted more effectively using TD. The nine batches of MA were classified using both extraction procedures. The nine batches were divided roughly into two groups using data from LLE. Subsequently, the groups were classified in detail using data from TD. TD can be used to provide supplemental information for LLE, and the combination of these extraction methods can be helpful for impurity profiling of MA.

Sulfur organic compounds in bottom sediments of the eastern Gulf of Finland

Background, Aims and Scope Despite the large number of studies on the forms of sulfur in marine deposits, investigations on sulfur organic compounds are still rare. It is known that the processes leading to formation of intermediate and final sulfur compounds (including organic ones) in modern deposits are the results of microbiological transformation of sulfur containing proteins, as well as the microbiological reduction of sulfate ions. The latter are finally reduced by anaerobic sulfate-reducing bacteria to H2S, HS− and S2−; the total sum of these is referred to as ‘hydrogen sulfide’ in chemical oceanography. Further, the formation of reduced sulfur organic derivatives (sulfides and polysulfides) is the result of interaction of the organic substance destruction products with the sulfide ions. In such cases, the main source of organic substances, as well as sulfates for the sulfur reducing processes, is the pore water in the sediments. The choice of the target of our study is based on the fact that the eastern part of the Gulf of Finland water area receives the bulk of the anthropogenic load of the St. Petersburg region. Low vertical intermixing of the water thickness is observed there (thus creating a deficiency of oxygen near the bottom), and the bottom sea current transfers the polluted salty water of the Baltic Sea into the Neva Bay. The whole of the above are the preconditions for the formation of sulfur-bearing organic compounds. A great number of bottom sediment samples for analytical surveys were collected in the Eastern Gulf of Finland during research expeditions in the years of 1997 and 2001. These were screened for structures of sulfur organic microcontaminants, including organic forms of sulfur, using advanced instrumentation and experienced personnel in our two, cooperating laboratories. This work is a part of the research being carried out on organic micro-admixtures present in bottom sediments, and is the summary of our findings on previously unstudied sulfur organic substances there.

Comparison of column phase configurations for comprehensive two dimensional gas chromatographic analysis of crude oil and bitumen

An inverted phase (polar to non-polar) column set has been compared with a non-polar to polar column set for the GC × GC separation of petroleum hydrocarbons. This column configuration is shown to provide greatly enhanced resolution for less polar compounds and makes greater use of the two dimensional separation space. It improves resolution of a greater number of components within one analysis and offers new possibilities for crude oil fingerprinting.

Gas chromatography and mass spectrometry of methoxylated polybrominated diphenyl ethers (MeO‐PBDEs)

Twenty-six methoxylated polybrominated diphenyl ethers (MeO-PBDEs) were characterized by gas chromatography (GC) on four different GC columns with different lengths and polarities, as well as by mass spectrometry using three ionization techniques, electron ionization (EI), electron capture negative ionization (ECNI) and positive ion chemical ionization (PICI). MeO-PBDE congeners with similar retention times on a nonpolar GC column were separated when analyzed on a polar GC column. EI can be used to determine the position of the methoxy substituent (ortho, meta or para) relative to the diphenyl ether oxygen in the MeO-PBDEs. The PICI ionization technique is shown to be valuable to generate structural information of the MeO-PBDEs, i.e. the degree of bromination on both the methoxy-substituted ring and the entirely brominated phenyl ring can be obtained. This structure information can also be achieved for certain MeO-PBDEs with the methoxy group in ortho position to the diphenyl ether bond in ECNI mode. Like other brominated compounds ECNI is preferable when analyzing environmental samples for quantification of MeO-PBDEs because of the formation of bromide ions, which enables low detection limits.

Towards Clean Fuels: Molecular‐Level Sulfur Reactivity in Heavy Oils

Heavy-oil desulfurization is an important process for the production of clean (ultra-low sulfur) transportation fuels. The relative reactivities of the sulfur compounds present in heavy oils (the graphic shows retention times for thiophenes (T) and annulated thiophenes on nonpolar and polar columns) are strongly dependent on the conditions of the desulfurization process.

Rapid, accurate, and sensitive fatty acid ethyl ester determination by gas chromatography-mass spectrometry

Fatty acid ethyl esters (FAEEs) are useful markers of ongoing alcohol use and may be associated with alcohol-induced damage to the liver and pancreas. In this article, we describe a novel method for rapid determination of the three major FAEEs found in human plasma. Internal standard, ethyl heptadecanoate, was added to plasma samples, and FAEEs were isolated by acetone precipitation, hexane lipid extraction, and amino-propyl silica solid phase extraction. FAEEs were quantitated by gas chromatography-mass spectrometry (GC-MS) using a nonpolar dimethylpolysiloxane column. The accuracy, precision, specificity, and sensitivity of the assay were defined from plasma samples from recently drinking and abstinent persons, with and without the addition of FAEEs. Individual FAEE peaks demonstrated excellent resolution. Instrument time was reduced by more than 60%. The lower limit of detection was 5 to 10 nM, and the lower limit of quantitation for each FAEE was 60 nM (for 22 samples with known concentration 60 nM, x +/-SD: 61 +/- 5.7, 57 +/- 5.7, and 57 +/- 5.9 nM, for ethyl palmitate, ethyl oleate, and ethyl stearate, respectively). Instrument precision (coefficient of variance, CV) for these three FAEEs was 0.3%, 0.4%, and 0.7%, respectively. Intra-assay precision (CV) for total FAEEs was less than 7%. FAEEs were absent in 49 samples from abstinent persons. FAEEs were detected in all 76 samples with associated positive blood alcohol levels. Our method of FAEE analysis is rapid and potentially useful in research and clinical studies. FAEE determination using this method is precise, accurate, sensitive, and specific and deserves broader application.

Simple analysis of four bisphosphonates simultaneously by reverse phase liquid chromatography using n-amylamine as volatile ion-pairing agent

Volatile organic amine was used as the mobile phase addictive during the separation of four bisphosphonates (alendronate, pamidronate, zoledronic acid and etidronate). An isocratic liquid chromatography method with evaporative light-scattering detection (ELSD) was developed for these bisphosphonates which are not retained on non-polar column and lack chromophore for detection. The analytes have sufficiently separated from each other on a Phenomenex C 18 column. The effects of mobile phase composition and instrumental parameters of ELSD were studied. This newly developed method enables direct measurement for analysis of bisphosphonates without the need of derivatization. This developed method provides high separation and specificity to bisphosphonate analysis. In quantitative analysis, the method showed satisfactory precision (less than 2.8%) and accuracy (higher than 94.4%), good linearity ( r = 0.9991–0.9997) and sufficient sensitivity (15–18 μg/ml). It can be easily and conveniently adopted for the routine quality control analysis.

Vapour pressures and enthalpies of vaporization of a series of the linear n-alkyl-benzenes

Vapour pressures and the molar enthalpies of vaporization Δ l g H m of the linear alkyl-benzenes C 6H 5C n H 2 n + 1 with the alkyl chain length n = 5, 7, 10, and 11 have been determined by the transpiration method. Kovat’s indices of the linear and branched alkyl-benzenes C 1 to C 16 were collected from the available literature. A linear correlation of enthalpies of vaporization Δ l g H m at T = 298.15 K of the alkyl-benzenes with the number of carbon atoms, as well as with the Kovat’s indices on the non-polar GC columns has been found. A simple GC-correlation approach for correlation and accurate predictions of vapour pressures and vaporization enthalpies of mono- and poly-alkyl-substituted benzenes has been suggested.

Identification, Synthesis, and Field Testing of the Sex Pheromone of the Citrus Leafminer, Phyllocnistis citrella

The citrus leafminer is an important vector of citrus canker in many of the major citrus production areas of the world. (7Z,11Z)-Hexadecadienal was reported as a sex attractant for this insect in the 1980s, based on trap catches during pheromone screening trials in Japan. However, attempts to reproduce this work in other areas of the world have not been successful. We report here that (7Z,11Z)-hexadecadienal is only one component of the pheromone, with the other critical component being the analogous trienal, (7Z,11Z,13E)-hexadecatrienal. Both compounds were identified in the effluvia from live female moths by coupled gas chromatography (GC)-electroantennography using nonpolar and polar GC columns, and the identifications were confirmed by comparisons of mass spectra with those of authentic standards. Stereoisomers of the two compounds, and a number of analogs, were synthesized to confirm the identifications. In field trials, neither compound alone was attractive to male moths, but blends of the two were highly attractive, with thousands of insects being caught per trial. Addition of the isomeric (7Z,11Z,13Z)-hexadecatrienal inhibited attraction to the two-component blend.

The use of two-dimensional GC–MS for the identification and quantification of low molecular weight compounds from high performance elastomers

A full characterisation of the low molecular weight compounds present in rubber compounds is becoming increasingly necessary due to the requirements of the food and pharmaceutical industries. It is important that manufacturers of medical devices, such as metered dose inhalers (MDI) and food contact rubber products, can provide information on the types and levels of compounds, including breakdown products, that may have the potential to migrate into drugs and foodstuffs. This knowledge is also of use in others areas, such as in occupational health or environmental areas, where the knowledge gained can form part of effective risk management strategies for workplace fume or external emissions. Better characterisation data on these low molecular weight components is also vital in reverse engineering work, where an improved knowledge of, for example, the breakdown products of a cure system can enable the analyst to provide the client with a more accurate formulation. The range of low molecular weight components present in rubber is complex and will include monomers and oligomers, manufacturing impurities and artefacts within compound additives, the additives (e.g. process aids, antidegradants and cure system species) themselves, as well as breakdown products. These breakdown products can originate from a number of sources, for example reaction products from components of the base polymer as a result of the thermal history of the compound, or products of additives such as curatives and antidegradants formed as a direct or indirect product of them performing their primary function in the compound. Gas-chromatography–mass spectroscopy (GC–MS) has been the analytical tool of choice for this type of investigative work for over thirty years due to its ability to separate the components that are present in a complex mixture and then identify them via their mass spectra. The recent advent of two-dimensional gas chromatography (GC×GC) associated with mass spectroscopy has provided the rubber analyst with a quantum step improvement as the use of a non-polar and polar GC column in series greatly enhances the resolving power available and it is now possible to identify and quantify compounds that were masked by other, more abundant compounds or by multiple compounds having similar retention times. Analysis work has been carried out on five high performance elastomer formulations to illustrate how the use of the two-dimensional GC–MS technique can provide a more complete characterisation of the low molecular weight fraction within such materials.