Capillary Column Gas Research Articles

Production of bio-fuels from cottonseed cake by catalytic pyrolysis under steam atmosphere

Abstract The purpose of this study is to evaluate the amounts of catalytic pyrolysis products of cottonseed cake in steam atmosphere and investigate the effects of both zeolite and steam on pyrolysis yields. The effect of steam was investigated by co-feeding steam at various velocities (0.6:1.3:2.7 cm s −1 ) in the presence of zeolite (20 wt% of feed). Liquid pyrolysis products obtained at the most appropriate conditions were fractionated by column chromatography. Elemental analysis and FT-IR were applied on both of these liquid products and their sub-fractions. The H/C ratios obtained from elemental analysis were compared with the petroleum products. The aliphatic sub-fractions of the oils were then analysed by capillary column gas chromatography. Further structural analysis of pyrolysis oil was conducted using 1 H-NMR spectroscopy. The characterization has shown that the bio-oil obtained from catalytic and steam pyrolysis of cottonseed cake was more beneficial than those obtained from non-catalytic and catalytic works under static and nitrogen atmospheres.

Permeability, porosity, and structure of monolithic capillary columns in gas chromatography

The permeability of monolithic silica gel capillary columns with respect to the helium carrier gas was studied using gas chromatography. The results obtained by gas chromatography and liquid chromatography were found to be in close agreement. The permeability of monolithic capillary columns was compared to that of hollow capillary columns and columns packed with finely dispersed sorbents. It was demonstrated that the permeability of the monolithic capillary columns studied is almost three orders of magnitude lower than that of hollow capillary columns of the same diameter but two orders of magnitude higher than that of columns packed with micron-scale particles. The interstitial fraction of the monolithic columns was found to be very high, 0.95.

Development of quantitative structure gas chromatographic relative retention time models on seven stationary phases for 209 polybrominated diphenyl ether congeners

Quantitative structure retention relationships (QSRRs) were developed to predict the gas chromatographic (GC) relative retention times (RRTs) for 209 polybrominated diphenyl ether (PBDE) congeners using the heuristic method included in the computer software Comprehensive Descriptors for Structural and Statistical Analysis (CODESSA). A total of 445 constitutional, topological, geometrical, electrostatic, and semi-empirical quantum chemical descriptors were derived for all PBDEs. Using experimental RRT data for 126 PBDE congeners from the literature, predictive regression models were built for seven individual GC capillary columns differing in stationary phases. Each model includes four descriptors which included Wiener index, Randic index, polarity parameter, etc., selected by CODESSA. High predictability was obtained. High multiple correlation coefficients R 2 indicated that >98.5% (except for stationary phase CP-Sil 19) of the total variation in the predicted RRTs is explained by the fitted models. The models were subsequently used to predict the RRTs of the remaining 83 PBDE congeners on seven different stationary phases. The statistical results show that, compared with others, DB-XLB column not only produces the least number of peak overlaps but also results in shorter retention times.

Formulation and Characterization of an Experimental PCB Mixture Designed to Mimic Human Exposure from Contaminated Fish

Each environmental exposure matrix contains a unique mixture of PCB congeners. Since several congener types have multiple and distinct biological actions, it is important to characterize congener profiles in exposure sources. The Fox River Environment and Diet Study (FRIENDS) is assessing the human health effects of consumption of PCB-contaminated fish from the Fox River in northeastern Wisconsin. Concurrent laboratory studies required the formulation of a dosing solution which closely mimicked the human PCB exposure from fish. PCB congener profiles from Fox River walleye were compared to profiles for various theoretical mixtures having different relative percentages of Aroclors by weight. The theoretical mixture which provided the best approximation of the Fox River fish PCB profile contained 35% 1242, 35% 1248, 15% 1254, and 15% 1260. A PCB mixture was formulated to match this theoretical construct, and the congener profile for the mixture of Aroclors was determined by capillary column gas chromatography with electron capture detection (GC/ECD). The relative percent of each congener was compared to the PCB congener profile of the theoretical Aroclor mixture and that for Fox River walleye. The specific congeners differed on average by 17% from the theoretical Aroclor mixture predicted values, and the specific congeners measured in the mixture were on average within 71% of those reported for Fox River fish. The mixture was found to have relatively low AhR activity but high RyR activity. Indirect comparisons suggest that in vivo toxicity was slightly greater than that for Aroclor 1254. This illustrates that Aroclor mixtures are useful for formulating dosing solutions which closely approximate actual environmental exposures.

In vivo biotransformation of metoprolol in the horse and on-column esterification of the aminocarboxylic acid metabolite by alcohols during solid phase extraction using mixed mode columns

The in vivo biotransformation of metoprolol tartrate in the thoroughbred racehorse was studied after administration of a single oral dose. Metoprolol and its basic and bifunctional phase I metabolites were isolated from urine and plasma using mixed mode solid phase extraction (SPE) cartridges. The isolates were derivatised as trimethylsilyl ethers and analysed by capillary column gas chromatography—positive ion electron ionisation and ammonia chemical ionisation mass spectrometry. Metabolism was primarily confined to the oxidative transformations of the p-(2-methoxy)ethyl substituent. Metoprolol and five phase I metabolites were detected in horse urine. In common with man, rat and dog, the zwitterionic compound (±)-4-(2-hydroxy-3-isopropylaminopropoxy)-phenylacetic acid (H117/04), was the principle metabolite in the horse. This compound was readily isolated from both plasma and urine samples by SPE and, in addition, an unusual on-column esterification of the carboxylic acid moiety by alcohols was observed. Metoprolol and the major aliphatic acid metabolite were detected for about 10 and 40 h, respectively in unhydrolysed urine. After enzymatic hydrolysis, the detection period increased to 15 and 60 h, respectively indicating some phase II metabolism of metoprolol and its metabolites in the horse.

Chromatographic Capillary Columns of Nonround Cross Sections

Two designs of gas-chromatographic capillary columns of nonround (rectangular) cross section with cross-sectional areas equal to that of a round capillary 0.16 mm in diameter were tested. It was found that capillary columns of nonround cross section with efficiencies of up to 500–600 theoretical plates per meter could easily be prepared.

Systematically structural identification of nitric compounds in crude oil with chemometric resolution

Aimed at the problem of classification of non-hydrocarbons of crude oil, the theoretical standpoint that the polarity of a compound depends on the whole structure and composition of molecule instead of a kind of heteroatom or its functional group was presented. A method was established for the systematically structural identification of nitric compounds in crude oil. The pre-fractionation of a crude oil sample into 7 fractions was performed by diadsorption column chromatography with neutral aluminum oxide and silica gel. Subsequently, the individual components were obtained by using capillary column gas chromatography, and the types of compounds were detected by a mass spectrometer. In combination with a chemometric resolution, the compounds of fraction were further identified. This method can relieve the difficulty of classical analysis in identifying those species with very low contents or without being completely separated. The structures of 168 nitric compounds in a crude oil sample were determined by this method.

Extraction and analysis of trace amounts of cyclonite (RDX) and its nitroso-metabolites in animal liver tissue using gas chromatography with electron capture detection (GC–ECD)

An efficient extraction and cleanup technique, and an instrumental detection method suitable for determination of trace amounts of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and its nitroso-metabolites in animal liver tissue were developed and validated in this paper. The method includes the extraction of explosives from liver tissue samples using accelerated solvent extraction (ASE) followed by cleanup using florisil and styrene-divinyl benzene (SDB) cartridges to remove interfering naturally endogenous compounds. The instrumental analysis was conducted using a capillary column gas chromatograph coupled with an electron capture detector (GC–ECD). High recoveries (58.9–106.8%) of RDX, hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX) were achieved at all concentrations studied. RDX, MNX, and TNX gave higher recoveries than DNX at all three tested concentrations (50, 250, 1250 ng/g). Overall recoveries of RDX, MNX, DNX, and TNX from 1 g beef liver samples containing 50, 250, and 1250 ng/g were 80.1, 82.8, 68.9, and 80.4%, respectively. The optimal injection port temperature range was 160–170 °C for analysis of RDX and its nitroso-metabolites. Higher or lower temperatures than 160–170 °C decreased signal amplitudes. RDX was unstable in the liver extraction matrix; as much as 50% of RDX was degraded 10 days after extraction if keeping the liver sample extracts at room temperature. Degradation of RDX to MNX, DNX, or TNX was not detected during the sample storage, extraction, or instrument analysis processes. Other optimized extraction and GC conditions are also discussed.

Milk fatty acid composition of goats grazing on alpine pasture

Interest in goat keeping in Slovenia has been growing recently, particularly in areas of higher altitudes, and on remote mountain and highland pastures. No literature data was found on the chemical composition of goat's milk produced on Alpine pasture. Therefore, the aim of our study was to determine the chemical milk composition of two dairy goat flocks kept at different altitudes, with the emphasis on milk fatty acid profile. The highland flock consisted of goats of the Saanen breed grazing at an altitude of 615–630 m, while the mountain flock consisted of goats of Alpine breed grazing at an altitude of 1060–1075 m. Goat keepers in Slovenia do not like keep more than one breed of goats together. The composition, free fatty acids (FFAs) and fatty acid (FA) profile of goat's milk collected from these two flocks grazing on Alpine pasture were determined. FA composition was determined by in situ transesterification and capillary column gas–liquid chromatography. Significant differences between the flocks were found for all components analysed ( P = 0.0019 for protein, P = 0.0001 for lactose, P = 0.0020 for total solids and P = 0.0010 for FFAs), except in fat content. The relationship between the FFA content and total fat was well described by the equation: FFA (mmol/l) = −0.1127 (%) + 0.4588 fat (%) − 0.0359 fat (%) 2, with R 2 = 0.73 and a S.D. of the error of 0.097 mmol/l, n = 40, for both flocks. The most abundant FAs in the milk of both flocks were C16:0, C18:1, n−9, C14:0 and C10:0. The average content of saturated FAs was 74.52 and 73.05% in milk from the higland and mountain flocks, respectively. Three saturated fatty acids (caprylic (C8:0), capric (C10:0) and lauric acid (C12:0)), were present at significantly higher amounts in milk from the highland flock than in milk from the mountain flock. Monounsaturated FAs represented 20.49 and 22.32% and polyunsaturated FAs 3.73 and 3.24% of the milk from the highland and mountain flocks, respectively. Among the monounsaturated FAs, palmitoleic + palmitelaidic acid (16:1, n − 7) showed a significantly higher concentration in milk from mountain flock than in milk from the highland flock. The content of linolelaidic acid (18:2, n − 6) was significantly higher in comparison to milk from the highland flock. The average quantity (32 mg 100 g −1 milk) of essential α-linolenic acid (18:3, n − 3) was slightly higher in milk of the highland flock than in milk from the mountain flock (26 mg 100 g −1 milk).

Methods to adjust for the interference of N2O on δ13C and δ18O measurements of CO2 from soil mineralization

In this paper we present an overview of the present knowledge relating to methods that avoid interference of N2O on delta13C and delta18O measurements of CO2. The main focus of research to date has been on atmospheric samples. However, N2O is predominantly generated by soil processes. Isotope analyses related to soil trace gas emissions are often performed with continuous flow isotope ratio mass spectrometers, which do not necessarily have the high precision needed for atmospheric research. However, it was shown by using laboratory and field samples that a correction to obtain reliable delta13C and delta18O values is also required for a commercial continuous flow isotope ratio mass spectrometer. The capillary gas chromatography column of the original equipment was changed to a packed Porapak Q column. This adaptation resulted in an improved accuracy and precision of delta13C (standard deviation(Ghent): from 0.2 to 0.08 per thousand; standard deviation(Lincoln): from 0.2 to 0.13 per thousand) of CO2 for N2O/CO2 ratios up to 0.1. For delta18O there was an improvement for the standard deviation measured at Ghent University (0.13 to 0.08 per thousand) but not for the measurements at Lincoln University (0.08 to 0.23 per thousand). The benefits of using the packed Porapak Q column compared with the theoretical correction method meant that samples were not limited to small N(2)O concentrations, they did not require an extra N2O concentration measurement, and measurements were independent of the variable isotopic composition of N2O from soil.

Determination of dichloroacetic acid and trichloroacetic acid in drinking water by acidic methanol esterification and headspace gas chromatography

A simple and rapid headspace method for gas chromatographic determination of dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) in drinking water was developed. Acidic methanol esterification followed by a headspace technique using a capillary column gas chromatograph (GC) equipped with an electron capture detector (ECD) was applied to determine the levels of DCAA and TCAA in drinking water. The major advantages of this method are the use of acidic methanol as the derivatization agent instead of the hazardous diazomethane, and esterification is carried out in water instead of organic solvent. DCAA and TCAA methyl esters produced in the reaction were determined directly by a headspace GC/ECD method. The linear correlation coefficients at concentrations ranging from 0 to 60 μg/L were 0.992 and 0.996 for DCAA and TCAA, respectively. The relative standard deviations (RSD, %) for the determination of DCAA and TCAA in drinking water were 15 and 21.3%, respectively ( n = 3 ). The detection limits of this method were 3 and 0.5 μg/L for DCAA and TCAA, respectively, and the recovery was 68–103.2% for DCAA and TCAA.

Chromatography and Computational Chemical Analysis for Drug Discovery

Analytical chemists have increasingly turned their attention to drug discovery and drug analysis and to solve fundamental questions of biological significance in physiology and genetics. New technologies have been developed, and a variety of instruments have been redesigned for biomedical applications. The development of high-performance liquid chromatography (HPLC) opened a new era in biorelated fields and allowed faster separations of fragile macromolecules. Capillary column gas chromatography (GC)/mass spectrometry (MS) have been used to achieve more powerful separation and to perform structural analysis of molecules, and laboratory automation including robotics has become a powerful trend in both analysis and synthesis. Liquid chromatography (LC)/MS is more suitable for biomedical applications than GC/MS because almost all biomolecules are heat sensitive. Furthermore, a combination of various mass spectrometers has been used even for proteins directly. Improving the sensitivity of nuclear magnetic resonance spectrometry (NMR) has permitted a direct connection with LC. Purification of biomolecules on-line by LC has been performed since the development of chip-electrophoresis, On the other hand, computational chemical analysis is a promising technique given the advancing the hardware and software for use in chemical fields. In this review, a combination of chromatography and computational chemistry for use in drug discovery studies is described. Fast LC analysis using a column switching technique was introduced for aromatic amino acid metabolites and guanidino compounds. Recent developments in related technologies are also included from review papers.

Brain Docosahexaenoic Acid Status and Learning in Young Rats Submitted to Dietary Long-Chain Polyunsaturated Fatty Acid Deficiency and Supplementation Limited to Lactation

N-3 fatty acid deficiency has been related to decreased docosahexaenoic acid (DHA) and increased docosapentaenoic acid (DPA) levels in brain and to learning disadvantages. The influence of n-3 deficiency and supplementation on brain fatty acids and learning were investigated in young rats. Newborn Wistar rats were assigned to three groups of cross-foster mothers. The control group (C) was nursed by mothers that received essential fatty acids during pregnancy and lactation, and the deficient group (D) was nursed by mothers that did not receive those fatty acids. The supplemental group (S) had the same conditions as D, receiving an additional DHA and arachidonic acid supplement during lactation. Cerebral cortex and hippocampus fatty acid composition was examined using thin-layer and capillary column gas chromatography, and learning was measured by passive-avoidance procedure. D brains showed low DHA and high DPA levels, but S brain composition was similar to C. Learning in the S group was unaffected, but in the D group, it was poorer than C. Learning was directly correlated with DHA levels and inversely with DPA levels in brain. Low DHA and high DPA brain levels both were correlated with poor learning. DPA seems not to be a suitable brain functional analogue of DHA, and DHA supplementation reversed both biochemical and learning adverse effects observed in n-3 deficiency.

Retention-time database of 126 polybrominated diphenyl ether congeners and two Bromkal technical mixtures on seven capillary gas chromatographic columns

The elution order of 126 polybrominated diphenyl ethers (PBDE) was determined for seven different gas chromatographic (GC) stationary phases. The resulting database facilitates selection of the most suitable GC columns for developing a quantitative, congener-specific BDE analysis and the testing of retention prediction algorithms based on structure relationships of GC phases and congener substitution patterns. In addition, co-elutions of the principal BDE congeners with other BDEs and/or with other brominated flame retardants were investigated and, as an application, the composition of two Bromkal mixtures (70-5DE and 79-8DE) was studied.

Separation of phytosterol oxidation products by combination of different polarity gas chromatography capillary columns

The number of characterized phytosterol oxidation products (POPs) from both ring- and side-chain structures has increased during recent decades, resulting in difficulties in the separation of POPs on different gas chromatography (GC) capillary columns. The main objective of this study was to separate a mixture of 29 purified and characterized oxidation products from sito-, campe- and stigmasterol using GC capillary columns with different polarity. For the first time in the area of POPs analysis, the separation efficiency of the combination of two capillary GC columns with different polarities was investigated. A non-polar 5% phenyl coated (DB5-MS) and a mid-polar 35% phenyl coated (DB35-MS) column was combined with a pressfit connector. The main improvement was enhanced base line separation for many of the analyzed POPs, compared with the separations achieved using the individual columns. However, three pairs of POPs co-eluted: 24-hydroxysitosterol/campesterol-5beta,6beta-epoxide, stigmasterol-5beta,6beta-epoxide/campesterol-5alpha,6alpha-epoxide and stigmasterol-5alpha,6alpha-epoxide/campestanetriol.

External quality assessment of urinary steroid profile analysis

Clinical samples were distributed on 10 occasions to six UK laboratories that perform urinary steroid profile analysis. Urine samples were from normal adult men and women, normal children and neonates. Samples from patients with Cushing's syndrome, virilization, adrenarche, obesity and congenital adrenal hyperplasia (21 and 17-hydroxylase defects) were also used for evaluation. Samples were analysed by capillary column gas chromatography (all laboratories) after hydrolysis of conjugates and derivative formation (five laboratories) or by variation of 17-oxogenic steroid methodology (one laboratory). For each distribution of samples, the performance of the participants was compared for quantitative analysis, and user comments were summarized. Quantitative results showed variation without necessarily biasing the result. Comments varied considerably in length. The interpretations did not always lead to a clear diagnosis or advise about appropriate further tests. This pilot urine steroid profiling scheme has clearly identified the requirement for external quality assessment. It is now hoped to offer this scheme worldwide in collaboration with the European Research Network for the Evaluation and Improvement of Screening, Diagnosis and Treatment of Inherited Disorders of Metabolism (ERNDIM).

Comparison of Series 5 gas chromatography column performances from a variety of manufacturers for separation of chlorinated dibenzo- p-dioxins and dibenzofurans using high-resolution mass spectrometry

An extended study of seven fused silica capillary gas chromatographic (GC) columns has been conducted with regard to separation of international toxic equivalent factor (I-TEF) isomers (tetra- through octa-chlorinated at 2,3,7,8 positions) of polychlorinated dibenzo- p-dioxins and polychlorinated dibenzofurans (PCDDs/PCDFs) from closely co-eluted other isomers using high-resolution gas chromatography–high-resolution mass spectrometry (HRGC–HRMS). The data are explicated in mass chromatograms of Series 5 GC columns from a variety of manufacturers (Varian CP-Sil 8 CB LowBleed/MS, Phenomenex ZB-5UMS, Agilent HP-5MS, Restek Rtx-5MS, Supelco Equity-5, J&W Scientific DB-5 and DB-5MS), according to relative retention times, and 2,3,7,8-substituted isomer concentrations for each of the columns tested. Results showed differences between 5% phenyl methyl silicone and 5% silphenylene (Si-arylene) silicone polymer type GC stationary phases in separation of 2,3,7,8-substituted PCDDs/PCDFs from closely co-eluted isomers. The separation differences for Si-arylene type columns resulted in lower toxic equivalence (TEQ) values compared to the siloxane-based columns. Because of differences in product nomenclature and manufacturing practices by various manufacturers, incorrect assumptions and comparisons may be made regarding the interchangeability of these columns for PCCD/PCDF separations. The data presented are the most comprehensive to date and provide a valuable addition to operational criteria for the standard US Environmental Protection Agency methods 1613b and 8290.

Ultrasonic extraction and capillary gas chromatography determination of nicotine in pharmaceutical formulations

A simple, rapid and accurate analytical method was developed for the determination of nicotine in pharmaceutical formulations. The method comprises a fast ultrasonic extraction (UE) with heptane as a solvent followed by direct capillary gas chromatography (GC) separation and quantitation. The application of ultrasound significantly accelerated the analyte extraction. For example, in the conventional method each extraction step takes up to 24 h whereas with the ultrasonic extraction method developed it took less than 20 min to achieve the same extraction efficiency. The ultrasonic extracts were directly chromatographed on an Alltech EC™-5 capillary GC column and a base line separation was achieved within 10 min. The consumption of environmental harmful organic solvent in this developed UE-capillary GC method is much lower than in conventional extraction-HPLC methods. The UE developed uses only 1/6 of organic solvent needed in conventional extraction. The subsequent GC analysis does not consume organic solvent as mobile phase while HPLC does. This green analytical method has been successfully applied to determine the nicotine content in both chewing and transdermal systems. Standard calibration curves were linear over the concentration range 1.00–500.0 μg/mL. Within-day and day-to-day relative standard deviations less than 1.9 and 2.0%, respectively.

Identification of Structures of Nitrogen‐Containing Compounds in Crude Oils in Conjunction with Chemometric Resolution

A universal method was established for the systematically structural identification of nitrogen-containing compounds in crude oils. Pre-fractionation of the non-hydrocarbons in a crude oil sample into 7 fractions was performed by di-adsorption column chromatography using neutral aluminum oxide and silica gel; subsequent high-resolution separation of individual components was achieved by using capillary column gas chromatography, and compound types were detected by mass spectrometer. The two-dimensional data from the compounds in the fractions were further resolved by a chemometric method to obtained the deconvoluted chromatogram and mass spectrum of every compound, and then, the nitrogen-containing compounds were identified in combination with the retention indices. This method could relieve the difficulty of classical analysis in identifying those species with very low contents or incompletely separation, particularly in the cases where the authentic standards were not available for addition into the unknown samples in order to reveal what indeed existed in them. The structures of 168 nitrogen-containing compounds in a crude oil sample were determined by this method with satisfactory results.

Comprehensive two-dimensional gas chromatography coupled with fast sulphur-chemiluminescence detection: implications of detector electronics

Within the petrochemical industry, there has been a growing interest in methods capable of providing detailed information on the distribution of sulphur-containing compounds in various product streams, going down to the level of separating and quantifying individual sulphur species. Since no single capillary gas chromatographic column is able to perform this separation, a refuge to multi-dimensional separation techniques has to be taken. In this respect, comprehensive two-dimensional gas chromatography (GC x GC) coupled with sulphur chemiluminescence detection (SCD) has shown to be highly promising. It has been suggested, however, that the detector volume of an SCD restricts its potential to keep up with the fast second-dimension separations of contemporary GC x GC. In this paper, we will demonstrate that the lack of speed of the SCD does not originate from its physical dimensions, but is largely determined by the speed of the electronics used. Additionally, some typical examples will be presented to illustrate the potential of GC x GC coupled with fast SCD.