Capillary Columns Of Different Polarity Research Articles

The Formation of Small Amounts of Cyclopropane during Pulsed Pyrolysis of C4–C5 Acyclic Alkanes in the Adiabatic Compression Reactor

During high-temperature pulse pyrolysis of acyclic butanes and pentanes under adiabatic compression conditions, cyclopropane, a stressed cyclic hydrocarbon, was found among the reaction products in small quantities for the first time. The analysis of the reaction products was performed by gas chromatography using three capillary columns of different polarity, selectivity and sufficient efficiency. The identification of reaction products, including cyclopropane, was performed using retention times of individual substances and model mixtures, as well as comparing chromatograms with reference chromatograms from the literature and the ScanView Application Database. It was shown that the chromatographic peak attributed to cyclopropane could not be a ghost peak. Additional confirmation of this conclusion was obtained in a series of experiments on the pyrolysis of n-butane at a reduced initial temperature of the adiabatic compression reactor (from 120 °C to 50 °C) and a modified mode of GC analysis. Cyclopropane yields as a function of maximum temperature have a bell-shaped asymmetric dependence. The maximum value of the yield of cyclopropane increases with the transition from normal alkanes to isoalkanes, and from pentanes to butanes; for n-pentane, 0.009 wt. %, and for isobutene, ≈0.017 wt. %. During the pulse pyrolysis of isobutane, n-butane, isopentane and n-pentane, cyclopropane is not a primary product. Further theoretical and experimental studies are needed to establish the mechanism of cyclopropane formation during pyrolysis of C4–C5 acyclic alkanes.

Synthesis of Small Libraries of Natural Products: Part II: Identification of a New Natural Product from the Essential Oil of Pleurospermum austriacum (L.) Hoffm. (Apiaceae).

Herein, comprehensive data of NMR, MS, IR, and gas chromatography (RI) obtained by GC-MS on commonly used capillary columns of different polarity (non-polar DB-5MS and polar HP-Innowax) of a series of esters of all constitutional isomers of hexanoic acid with a homologous series of ω-phenylalkan-1-ols (phenylmethanol, 2-phenylethanol, 3-phenylpropan-1-ol, 4-phenylbutan-1-ol, and 5-phenylpentan-1-ol) and phenol, in total 48 chemical entities, were collected. The created synthetic library allowed the identification of a new constituent of the P. austriacum essential oil (3-phenylpropyl 2-methylpentanoate). The accumulated spectral and chromatographical data, as well as the established correlation between RI values and structures of regioisomeric hexanoates, provide (phyto)chemists with a tool that will make future identification of related natural compounds a straightforward task.

Validation of an improved European standard method for the determination of PCBs in oil samples

Two European standard methods (EN 12766 and EN 61619) are currently used for the determination of PCBs in specific oil matrix. However, apolar matrix compounds (e.g. hydrocarbons) elute from the adsorbent together with the PCBs and are injected into the analytical system where their presence contaminates the inlet, detectors and columns; and decreases system performances. Insufficient cleanup causes delay of elution of PCBs from GC columns. By using new sulfoxide-bonded silica, PCBs are better separated from aliphatic hydrocarbons because the specificity of the stationary phase for these compounds is much higher that that used in both standard methods. A gas chromatograph AT6890 with two capillary columns of different polarities (HP-5MS and DB-1701) coupled to two μECDs is used. Oven temperature program is as followed: 90°C (1 min), 70°C/min to 180°C, 5°C/min to 230°C (0.1 min), 1.5°C/min to 280°C. Run time is 46 min. The procedure was validated through regular analysis of blanks, fortified samples (transformer oil, motor used and unused oil) and certified materials (BCR-449 and BCR-420, waste mineral oils, high and low PCB levels). Two internal standards were used (PCB 30 and PCB 209). An average recovery ± RSD of 82.8 ± 5.4 % was achieved for all six PCBs in different matrices. The LOQ per single PCB congener is 0.2 mg kg-1. The average recovery ± RSD for the BCR-420 is 92.0 ± 4.6 % and for the BCR-449 is 105 ± 2.5 % for all certified PCBs in waste oils.

A series of esters of diastereomeric menthols: Comprehensive mass spectral libraries and gas chromatographic data

A comprehensive data collection of mass spectral and gas chromatographic data of a series of esters of diastereomeric menthols (menthol, isomenthol, neomenthol, and neoisomenthol), in total 150 chemical entities, obtained by GC–MS on commonly used capillary columns of different polarity (non-polar HP-5MS and polar HP-Innowax), was created. Also, MS libraries containing electron ionization MS recorded on single quadrupole as well as on quadrupole ion-trap mass detectors together with the RIs on non-polar and polar columns were compiled (available as supplementary materials). The results point out to frequent misidentification of neoisomenthyl acetate as isomenthyl acetate in the literature, and the means of how to resolve this issue was suggested. The outcomes of this study provide chemists and food technologists with a useful tool in the field of food analysis of compounds with important food aroma properties.

Study on Lavender Essential Oil Chemical Compositions by GC-MS and Improved pGC.

Lavender essential oil from the aerial parts of Lavandula angustifolia Mill. was analyzed by GC-MS equipped with three capillary columns of different polarities, which were HP-1, HP-5 ms and HP-INNOWax. A total of 40 compounds were identified by GC-MS, accounting for 92.03% of the total essential oil compositions. Nineteen monomers were separated by column chromatography and improved preparative gas chromatography (pGC), six of which could not be retrieved from the NIST 14 (National Institute of Standards and Technology, USA; 14th edition) library database. Fifteen compounds were identified for the first time in lavender essential oil. The improved pGC not only doubled the efficiency but also greatly reduced the cost.

Gibbs energy additivity approaches to QSRR in generating gas chromatographic retention time for identification of fatty acid methyl ester.

The Gibbs energy additivity method was used to correlate the retention time (t R) of common fatty acid methyl esters (FAMEs) to their chemical structures. The t R of 20 standard FAMEs eluted from three capillary columns of different polarities (ZB-WAXplus, BPX70, and SLB-IL111) under both isothermal gas chromatography and temperature-programmed gas chromatography (TPGC) conditions were accurately predicted. Also, the predicted t R of FAMEs prepared from flowering pak choi seed oil obtained by multistep TPGC with the BPX70 column were within 1.0% of the experimental t R. The predicted t R or mathematical t R (t R(math)) values could possibly be used as references in identification of common FAMEs. Hence, FAMEs prepared from horse mussel and fish oil capsules were chromatographed on the BPX70 and ZB-WAXplus columns in single-step and multistep TPGC. Identification was done by comparison of t R with the t R of standard FAMEs and with t R(math). Both showed correct identifications. The proposed model has six numeric constants. Five of six could be directly transferred to other columns of the same stationary phase. The first numeric constant (a), which contained the column phase ratio, could also be transferred with the adjustment of the column phase ratio to the actual phase ratio of the transferred column. Additionally, the numeric constants could be transferred across laboratories, with similar correction of the first numeric constant. The TPGC t R predicted with the transferred column constants were in good agreement with the reported experimental t R of FAMEs. Moreover, hexane was used in place of the conventional t M marker in the calculation. Hence, the experimental methods were much simplified and practically feasible. The proposed method for using t R(math) as the references would provide an alternative to the uses of real FAMEs as the references. It is simple and rapid and with good accuracy compared with the use of experimental t R as references.

Chemical Variability of Ivoirian Xylopia rubescens Leaf Oil.

Forty-two essential oil samples were isolated from leaves of Xylopia rubescens harvested in three forests of Southern Ivory Coast. All the samples have been submitted to GC-FID and the retention indices (RIs) of individual components have been measured on two capillary columns of different polarity. In addition, 20 oil samples, selected on the basis of their chromatographic profile, were also analyzed by 13 C-NMR and 24 components (78.0-92.4% of the whole compositions) have been identified. The content of the main components varied drastically from sample to sample: furanoguaia-1,4-diene (5.7-54.1%), furanoguaia-1,3-diene (1.1-10.5%), (8Z,11Z,14Z)-heptadeca-8,11,14-trien-2-one (4.3-16.0%), and (E)-β-caryophyllene (1.7-17.3%). Hierarchical cluster and principal components analysis of the 42 oil compositions allowed the distinction of two well-differentiated groups of unequal importance within the oil samples. Oil samples of the main group (Group II) contained mainly furanoguaia-1,4-diene (mean [M]=43.1%; standard deviation [SD]=3.2%) while furanoguaia-1,3-diene (M=8.4%; SD=0.9%) and (8Z,11Z,14Z)-heptadeca-8,11,14-trien-2-one (M=7.1%; SD=1.5%) were present at appreciable contents. The composition of Group I was dominated by furanoguaia-1,4-diene (M=17.0%; SD = 8.5%), (8Z,11Z,14Z)-heptadeca-8,11,14-trien-2-one (M=10.2%; SD=2.4%) and (E)-β-caryophyllene (M=9.5%; SD=5.3%).

The development of the method for the determination of the low-molecular weight alcohol content in the specimens of the biological materials

The objective of the present study was the development and metrological attestation of the method for the determination of concentrations of low-molecular weight (C1-C4) alcohols and acetone in the biological materials, such as urine and blood including partially dehydrated blood. The method is based on the chromatographic analysis of the equilibrium vapour phase with the use of the static headspace autosampler. The calculations were carried out making use of the results obtained with the application of propanol-1 as the internal standard. In order to enhance the reliability of the identification of the analytes in the complex blood matrix, the two-channel configuration was employed that consisted of a single evaporator, passive flow division, two capillary columns of different polarity, and two flame ionization detectors. The proposed technique provided for the first time the unique possibility to perform the quantitative measurement of the internal standard in the starting specimen before the main analysis. The validated procedure for the quantitative determination of the alcohol concentration of blood samples with the reduced water content has been described. The present study made it possible to collect the total amount of relevant statistical data necessary to calculate the metrological characteristics of the method in question. The method was certified based at D.I. Mendeleev All-Russian Research Institute of Metrology under No 754/242-(01.00250)-2016.

Retention Indices for Identification of Aroma Compounds by GC: Development and Application of a Retention Index Database

In this paper we focus on the development and application of a retention index database for aroma compounds with high structural diversity. Retention indices of over 300 aroma compounds were determined on three capillary columns of different polarity. The capability of the retention index database was evaluated by identification of the components of tobacco flavor. The results showed that the database can be used for qualitative identification. The database also contains a good set of retention index data for study of quantitative structure–retention relationships.

Separation of closely eluting chloronaphthalene congeners by two-dimensional gas chromatography/quadrupole mass spectrometry: An advanced tool in the study and risk analysis of dioxin-like chloronaphthalenes

Two capillary columns of different polarity were applied in a two-dimensional gas chromatography system coupled to a quadrupole mass spectrometric detection (GCxGC/qMS) in order to separate and identify all of the possible 22 isomers of tetra-, 14 of penta- and 10 of hexachloronaphthalene that may occur in selected industrial chemicals. The two-dimensional GCxGC separation was achieved using Rt-β DEXcst and DB-WAX phases, and data imaging was done by 2D and 3D mapping. This combination allows for the analysis of all tetra- to hexachloronaphthalene congeners in a single instrumental run without any pre-separation or fractionation of the analytes. The novel methodology described here can assist in the accurate determination and expression of dioxin-like toxicity of tetrachloronaphthalenes to octachloronaphthalene that are usually present as mixtures at least in abiotic materials such as technical chloronaphthalene formulations (e.g. Halowax mixtures), and wastes containing Halowaxes and other CN formulations.

GC-MS Analysis of Volatile Constituents of Cornus mas Fruits and Pulp

Cornus mas is a tree bearing edible fruits, known for its traditional homemade beverages and preserves and for its usage as a traditional medicinal plant. There are no references cited in the literature for the volatile components of mature fruits and their pulp (product that is commercially available). The aim of the present study was the identification of the volatile constituents of Cornus mas pulp and mature fruits by GC-MS using capillary columns of different polarity and selectivity. The analysis showed that Cornus mas pulp is rich in fatty acid methyl/ethyl esters, while mature fruits have higher content of alcohols, aldehydes and terpenes. Additionally, the use of two or more capillary columns of different polarity and selectivity could be the key to a much more integrated analysis and a much more accurate identification of the components of natural complex mixtures such as volatile constituents of Cornus mas or other plants.

Chemical composition and antimicrobial activity of the essential oil of Cacalia tangutica (Maxim.) Hand.-Mazz

Essential oil of the subterranean part of Cacalia tangutica (Maxim.) Hand.-Mazz was analyzed by gas chromatography (GC)-mass spectrum (MS) technique in two different capillary columns of different polarities. Thirty-one components were identified in the oil and the main compounds were α-zingiberene (13.49%), germacrene D (10.76%), α-pinene (8.54%), caryophyllene(Z-) (6.36%), linalool (6.16%), β-myrcene (4.89%), β-ocimene (Z-) (4.40%)and ocimenone(Z-) (3.58%). The antimicrobial activity of the oil was evaluated against 2 fungi and 12 bacteria including 6 clinically isolated strains using the agar disc diffusion and broth microdilution methods. The results show that the oil presented a broad antimicrobial spectrum and had better antimicrobial activity against yeast and gram-positive bacteria. The minimum inhibitory concentration values were 0.16–5.00 g/L and minimum bactericidal concentration values were 0.16–5.00 g/L.

Composition of the essential oil of Petagnaea gussonei (Sprengel) Rauschert, a relict species from Sicily (Southern Italy)

AbstractThe essential oil from leaves, stems and roots of Petagnaea gussonei (Sprengel) Rauschert ( = Petagnia saniculifolia Guss.), endemic to the Nebrodi Mountains (Sicily, Italy), has been analysed by the gas chromatography–mass spectrometry (GC–MS) system on two fused‐silica capillary columns of different polarities. A total of 94 components were identified. Quantitative and qualitative differences were found among the analysed parts. The principal compounds from the leaves oil were found to be (w/w%) germacrene D (19.9%), γ‐muurolene (7.96%) and caryophyllene oxide (6.85%), while in the oil from stems hexadecanoic acid (23.40%), germacrene D (18.50%) and (Z,Z)‐9,12‐octadecadienoic acid (13.20%) were the main constituents. The oil from the roots presented instead hexadecanoic acid (21.50%), 4‐vinylguaiacol (6.81%) and germacrene D (5.22%) as the major constituents. A comparison with essential oils from taxonomically‐related species of P. gussonei is reported. This is the first report on the chemical composition of this species. Copyright © 2008 John Wiley & Sons, Ltd.

A Comparative Study of the Composition of the Leaf Oils of Three Litsea species from Borneo

The chemical components of the leaf oils of Litsea resinosa Bl., L. gracilipes Hook. f. and L. paludosa Koesterm. were identified by co-chromatography with authentic samples on two capillary columns of different polarity, GC/MS and linear retention indices. The leaf oils were made up mainly of sesquiterpenoids. The oil of L. resinosa could be differentiated from the other samples due to its high contents of bulnesol (14.9%), β-caryophyllene (10.2%), β-elemene (10.2%) and other sesquiterpenoids. Ledene (9.0%) and aromadendrene (8.3%) were the major constituents in the leaf oil of L. gracilipes. Of the Litsea oils studied, this oil contained the highest concentrations of monoterpenoids with p-menth-1-en-9-ol (1.4%) as the major representative. The leaf oil of L. paludosa was found to possess some compositional similarities to the leaf oil of L. gracilipes but it could be distinguished from the latter by the significant presence of elemol (7.7%), γ-cadinene (2.9%), γ-eudesmol (2.8%), selin-11-en-4α-ol (2.3%), α-cadinene (2.1%), palustrol (1.7%) and selina-3,7(11)-diene (1.1%).

Serially coupled capillary columns supercritical fluid chromatography with midpoint pressure control

Two capillary columns of different polarities were coupled in series by means of a coupling restrictor. The pressure of the first column and the midpoint pressure (between the coupling restrictor and the second column) were controlled independently of each other using two pumps. The selectivity of this separation system was highly dependent on the pressure difference and could be continuously changed between those of two columns. The pressure difference could be changed even in course of separation for fine tuning of the selectivity. Several examples were shown to demonstrate the utility of this method.

Headspace-SPME-GC-MS Identification of Volatile Organic Compounds Released from Expanded Polystyrene

A method for the identification of volatile organic compounds (VOCs) released from packaging expanded polystyrene (EPS) is presented. Headspace solid-phase microextraction (HS-SPME) with a 75-μm carboxen-polydimethylsiloxan fiber was used as sample preparation technique before the determination of the volatile organic compounds by gas chromatography–mass spectrometry (GC-MS). For separation of compounds, two fused silica capillary columns of different polarity (DB-5ms and BPX-50) were used. Styrene monomer with his impurities and oxidation products, as well as residual pentane, were identified in the headspace of EPS.

Comparison of classical and ultrasound-assisted extractions of steroids and triterpenoids from three Chresta spp

A comparative study of classical and ultrasound-assisted extractions of steroids and triterpenoids from stem, leaves and flowers of Chresta exsucca, C. scapigera and C. sphaerocephala is described. The direct analysis of crude apolar and medium-polar extracts has been conducted by high-resolution gas chromatography followed by co-injections of the crude extract with certified standards on capillary columns of different polarities. The use of ultrasound decreased significantly the total time of treatment and in addition, this extraction method was more effective for the steroids and most of the triterpenes.

GC Behavior of disaccharide trimethylsilyl oximes.

Twenty-five disaccharides are converted to trimethylsilyl oximes and injected on two capillary columns of different polarities (methyl and phenyl-methyl silicone). Their Kovats retention indices are determined at three temperatures. Multivariate data analysis is used in order to obtain relations between retention and some structural features. Phenylmethyl silicone have better chromatographic characteristics for the assayed compounds. The two columns can provide useful chromatographic information when a very complex disaccharide mixture has to be analyzed.

Serially coupled capillary columns supercritical fluid chromatography with a coupling restrictor.

A serially coupled column system for capillary supercritical fluid chromatography was constructed by connecting two capillary columns of different polarities using or without using a coupling restrictor. The influence of the column sequence, the size of the coupling restrictor and the column temperature on the polarity of the system were studied. The system without a coupling restrictor (the directly coupled system) provided an intermediate polarity between two columns, depending on the column geometry, such as the film thickness and column length, although it slightly shifted to that of the first column. In the system with a coupling restrictor, the contribution of the second column to the overall retention increased with its resistance. The use of a coupling restrictor allowed to control the polarity of the coupled system virtually over the whole range between two columns. The temperature was an additional effective parameter for tuning the polarity of the system.

Sesquiterpene, alkene, and alkane hydrocarbons in virgin olive oils of different varieties and geographical origins.

The hydrocarbon fraction of 30 virgin olive oils was analyzed, focusing in particular on the sesquiterpenes. The oil samples were of different geographical origins and obtained from different olive varieties. The hydrocarbon fraction was isolated by silica gel column chromatography of the unsaponifiable fraction of the oils. The sesquiterpene hydrocarbons were then fractionated, on the basis of their degree of unsaturation, by AgNO3 TLC and silica gel AgNO3 column chromatography. The composition of the sesquiterpenes was more complex than previously reported. Among the 31 sesquiterpenes detected, 24 have been tentatively identified, by comparison of the linear retention indices on two capillary columns of different polarities and mass spectra with those reported in the literature. The total concentration of the sesquiterpenes in the oils analyzed ranged from about 2 to 37 ppm. Among the sesquiterpenes the more abundant were alpha-farnesene, alpha-copaene, eremophyllene, and alpha-muurolene. The alkenes present in the hydrocarbon fraction were isolated by TLC AgNO3 and characterized by GC-MS of their dimethyl disulfide derivatives. The series of n-Delta9-alkenes from C22 to C27, 8-heptadecene, and 6,10-dimethyl-1-undecene were detected. Among the n-alkanes, those with an odd number of carbon atoms predominated in all of the analyzed oils, the most common being C23, C25, C27, and C29. The concentration of the n-alkenes ranged from about 0.5 to 2 ppm, whereas for the n-alkanes the range was from 30 to 177 ppm.