bluuebunny/crossref_metadata_2025_split huggingface dataset:
Shifting of gas chromatographic retention times due to solvent effects — a study using sulfur chemiluminescence detection
Authors: Dietz Edward A. 
Published: May 2005

AbstractGas chromatrography (GC) with sulfur chemiluminescence detection (SCD) is an outstanding combination for selectively determining trace concentrations of sulfur compounds in hydrocarbon samples. GC peaks can be identified by retention times when reproducible, automated injection techniques are used. However, as described in this work, analysts should be on the look out for retention shifting due to solvent effects from sample components. Three examples of retention shifting are presented: (1) thiophene by benzene; (2) methylthiophenes by toluene; and (3) dibenzothiophene by gas oil. Depending on samples and analysis conditions, retention shifts from a few hundredths to 1.5 min have been observed. Such retention shifts are likely to cause errors in peak identifications. Therefore, when using SCD, simultaneous FID monitoring is recommended as an aid in evaluating chromatograms for possible retention shifting due to solvent effects.
Effect of high temperature in determination of the mathematical dead time and the constants of the n‐alkane retention time curve in gas chromatography
Authors: Didaoui L. , Touabet A. , Meklati B. Y. 
Published: May 2005

AbstractIn gas liquid chromatography, the column dead time and the constants of the n‐alkane retention time curve are calculated by the multiparametric least‐squares regression iterative method at high temperature between 180 and 270°C. The method was applied to two types of columns. The first group includes eight packed columns (seven OV polymethylphenylsiloxane and Apolane‐87), while the second includes five glass capillary columns (four methylsilicone with different film thicknesses and Apolane‐87). The calculated tM and b values were compared with those obtained by Guardino's, Grobler's, and Kaiser's methods. The influences of coating thickness and temperature thereon were investigated.
Off‐line SFE‐CGC‐ECD analysis of 2,4‐D and Dicamba residues in real sugar cane, rice and corn samples
Authors: Lanças Fernando M. , Rissato Sandra R. , Mozeto Antonio A. 
Published: May 2005

AbstractDetermination of 2,4‐D (2,4‐dichlorophenoxyacetic acid) and Dicamba (2‐methoxy‐3,6‐dichlorobenzoic acid) residues in sugar cane, rice, and corn was carried out both by solid liquid extraction (SLE), as already described in the literature, and by a supercritical fluid extraction (SFE) method developed in our laboratory. The extracts were esterified and cleaned‐up by passing through a Florisil column. Extracts were analyzed by high resolution gas chromatography, with electron capture detection. The tested methods presented good recoveries (above 90%); the SFE CO2/acetone method showed better extraction efficiencies (extracted 30 % more herbicide in real samples), shorter extraction time and lower organic solvent consumption than the SLE method.
Capillary electrophoresis with constant potential amperometric detection using a nickel microelectrode for detection of carbohydrates
Authors: Fermier Adam M. , Colón Luis A. 
Published: May 2005

AbstractCarbohydrates were separated by capillary electrophoresis (CE) and detected electrochemically using a nickel microelectrode which was operated at a constant applied potential (∼0.6 V vs. Ag/AgCI). A simple capillary electrode holder design facilitated alignment between the separation capillary and the working microelectrode without the use of micro‐positioning equipment. The separations were performed under alkaline conditions (pH > 11), matching the high pH requirements for amperometric detection at the nickel electrode. The analytical procedure developed showed detection limits for the carbohydrates studied in the micromolar range, showing a linear response in the range tested (micromolar to millimolar). The procedure was used to identify sugars in two real samples (i.e., urine and in a common beverage). The potential use of the system for the determination of amino acids was also demonstrated.
Trace analysis of hetero aromatic compounds (NSO) in water and polluted groundwater by Solid phase micro‐extraction (SPME)
Authors: Johansen Sys Stybe , Pawliszyn Janusz 
Published: May 2005

AbstractBy using Solid Phase Micro‐Extraction (SPME) and Capillary Gas Chromatography (CGC) a method was developed to analyze hetero aromatic compounds (NSO) in water. Compounds with nitrogen, sulfur, or oxygen in the aromatic ring system are found in creosotecontaminated groundwater. NSO are highly water‐soluble, toxic, and have adverse organoleptic characteristics. SPME is a fast, simple, and solvent‐free sample preparation technique that involves exposing a polymer coated fiber to a sample to extract contaminants. Different fiber coatings were tested, and polyacrylate was found to extract NSO in the highest amounts and to be most versatile. Extraction was strongly enhanced by salting. The optimized SPME method combined with CGC coupled to an ion trap mass spectrometer (ITMS) has detection limits of 20–40 ng/L for the semi‐volatile and 1–10 μg/L for the volatile NSO, response linear with respect to concentrations over three orders of magnitude, and precision of 3–14% relative standard deviation. The method was evaluated using real creosote‐contaminated groundwater samples and feasibility was demonstrated. SPME‐CGC/ITMS allows an unequivocal identification and quantification at a low NSO level in environmental samples.
Separation and analysis of nitroarenes from airborne particulate organic matter by HPLC and capillary GC‐MS methods
Authors: Warzecha Lidia 
Published: May 2005

AbstractNormal‐phase HPLC has been applied to the separation of nitroarenes from dichloromethane extracts from airborne particulate matter samples collected in urban regions of Upper Silesia. GC‐MS and capillary gas chromatography with NP detector analysis of the nitroarene fraction made it possible to identify and determine quantitatively those compounds which dominate in the organic matter emitted to the atmosphere in highly industrialized regions (2‐nitrofluorene, isomeric nitroarenes of MW = 247, i.e. nitropyrene/nitrofluoranthene/nitroacephenanthrylene).
Silicalite as a stationary phase for HPLC
Authors: Dumont Philip J. , Fritz James S. 
Published: May 2005

AbstractA molecular sieve known as Silicalite was used as the column packing for HPLC. Silicalite contains channels (or cavities) approximately 6 Å in diameter but, unlike most other molecular sieves, Silicalite is hydrophobic. The retention times of methyl ketones and substituted phenols containing n‐alkyl groups increase with increasing chain length of the substituent. However, phenols with very bulky substituents appear to be excluded from the Silicalite channels and elute very quickly. Excellent separations were obtained for a number of compounds with only slight differences in chemical structure. These include phenol isomers with a primary‐ or secondary alkyl group, position isomers of substituted phenols, and aliphatic cis‐trans isomers.
Whey proteins eluted reversed phase gradients
Authors: de Frutos Mercedes , Cifuentes Alejandro , Diez‐Masa Jose Carlos 
Published: May 2005

AbstractThe behavior of bovine whey proteins in Reversed‐Phase High Performance Liquid Chromatography (RP‐HPLC) systems has been investigated. The Linear Solvent Strength (LSS) model has been applied to the separation of these proteins studying how their retention time and band broadening change when different gradient parameters are modified. From our results it is deduced that the LSS model describes the behaviour of the whey proteins in RP‐HPLC. Also, it seems that ts (the retention time for non‐retained solutes) depends on the size of these proteins. The good fit observed between experimental data and the equations deduced from the LSS model allows the prediction of a gradient shape that permits a rapid analysis of the above mentioned proteins.
Micellar electrokinetic capillary chromatography of algal toxins
Authors: John Wilson , Raynor Mark W. , Rae Bruce 
Published: May 2005

AbstractRecent methods employed for the analysis of algal toxins have focused on high performance liquid chromatography. However these methods suffer from poor resolution, poor efficiency, and long analysis times. This study involves the investigation of a number of toxins including nodularin, microcystin LR, YR, and RR which are cyclic peptides produced by strains of blue‐green algae. The electroseparation mode was micellar electrokinetic capillary chromatography (MECC) using a borate buffer containing sodium dodecyl sulfate (SDS) as the surgactant of choice. The method was optimized with standard toxin compounds and employed for the screening opf toxins in supercritical fluid extracts (SFE) of freeze‐thawed algal scum samples.
New stationary phases of conjugated π‐electron systems for HPLC—characterization of structure and dynamics by solid state NMR spectroscopy
Authors: Ellwanger Arndt , Brindle Rainer , Albert Klaus 
Published: May 2005

AbstractFour new stationary phases for HPLC were prepared by modifying silica gel with a trifrnctional aminoalkyl silane. A conjugated π‐electron system was linked to the amino group either directly or with a carboxylic anhydride as a spacer in between. Characterization and dynamic measurements of the new stationary phases were performed by solid state NMR spectroscopy. The results of the 29si and 13C CP/MAS techniques were compared with the recently developed 1H MAS‐only technique. Despite strong homonuclear dipole‐dipole interactions it was possible to obtain well resolved 1H MAS spectra of those stationaru phases with a high degree of crosslinking. Limited mobility of the aromatic ligand fragments is common for all examined stationaryu phases.The chromatographic properties of the new phases were tested by their ability tio sepatate a mixture of eight PAHS. It could be shown that the π‐π interaction mechanism is responsible for the separation of the eight PAHs, because the elution order of the PAHs did not changem despite the use of both a nonpolar mobile phase (n‐heptane) and a polar mobile phase (methanol/ water mixture).
Rapid analysis of unsaturated acidic xylooligosaccharides from kraft pulps using capillary zone electrophoresis
Authors: Rydlund Annika , Dahlman Olof 
Published: May 2005

AbstractSeveral acidic xylooligosaccharides containing unsaturated “hexenuronic acid” units, i.e. 4‐deoxy‐L‐threo‐hex‐4‐enopyranosy‐lurinic acid (4‐ΔU) units, were separated as their alditol derivatives by capillary zone electrophoriesis in 438 mM borate buffer (pH 10.3) and were detected selectively at the μM level on‐column UV detection at 232 nm. These acidic oligosaccharides were obtained from birch and pine kraft pulps on enzymatic hydrolysis with endoxylanases and subsequent treatment with other Trichoderma reesei enzymes. Under the conditions empolyed, acidic 4‐ΔU‐containing xylooligosaccharides with a molecular size renging from trisaccharides up to nonasaccharides could be separated. Oligosaccharides with higher molecular mass were detected first. Two 4‐ΔU‐xylotetraose isomers, with the 4‐ΔU‐group linked to different xylose units in the iligosaccharide backbone, could be resolved from each other with a resolution of about 1. By using a disaccharide (4‐ΔU α‐(1 → 4) linked to N‐acetyl glucosamine) as a model compound the minimum detectable concentration was determined as 10 μM.
On‐line LC‐GC‐AED and LC‐GC‐MS – multidimensional methods for the analysis of PAC in fuels, combustion emissions and atmospheric samples
Authors: Lewis Alastair C. , Askey Sarah A. , Holden Krystyna M. , Bartle Keith D. , Pilling Michael J. 
Published: May 2005

AbstractThe composition and concentration of polycyclic aromatic compounds (PAC) in fuels. Theier combustion products and in the atmosphere remains a topic of considerable interest. Despite the wealth of literature on the identification of PAC, speciation at low concentrations remains difficult due to instrument limitation and the complexity of fuel and environmental samples. Consequently on line sample preparation procedures (SPE, SFE, LC, etc.) are becomeing an increasingly important step in the analysis procedure particularly where sample clean‐up and fractionation are essential for improving analytical resolution. In this study a normal phase high pressure analytical resolution. In this study a normal phase high pressure liquid chromatography‐gas chromatography (LC‐GC) system has been developed to provide quantitative analysis of samples, as diverse as coal liquids, petroleum fuels, diesel exhaust particulates, and urban air particulates. Separation and identification of parent and alkylated PAH, hetercycline nitro‐and oxy‐PAC can be achieved by direct coupling to an atomic emission detector and a bech top mass spectrometer. For both systems the primary LC separation combined with the large sample volume transferred to GC vastly improves detection limits. Furthermore the complimentary nature of the two detectors used enables the positive indentification of many unknowns.
HPLC assay of underivatized free amino acids with column switching and evaporative light‐scattering detection
Authors: das Neves Higuinaldo J. Chaves , Morais Zilda Braga 
Published: May 2005

AbstractIn this communication the authors report the HPLC SEPARATION OF 20 amino acids without derivatization. Separation was achieved by column swithing using a C‐8 reversed‐phase column and a cationic ion‐exchange column. Detection of the underivatized amino acids was accomplished by means of an evaporative laser light‐scattering (ELS) detector. The influence of the temperature of the diffusion tube and nebuolzation gas pressure on detector response is reported. The relationship of peak areas vs. mass show a good log‐log linearity within a 1:10 range. Detechtion limit is in the order of 200 pmol for most amino acids under the conditions used.
Maximum transfer condition for spitless injection
Authors: Kaufmann Anton 
Published: May 2005

AbstractSplitless injection conditions were optimized by the use of experimental designs (2‐level factorial and central composite designs). Modified parameters were: Type of liner, injection volume, solvent, temperature, splitless time. A prolonged splitless time, considered to be an important parameter, proved to be statistically insignificant. This leads to the conclusion that analytes can penetrate the dead volume between column entrance and split valve. To prevent any penetration of solvents, a small reversed split flow was introduced. It could be shown that this auxiliary flow allows an almost complete transfer of solvents. To further speed up the transfer process, a liner modification was proposed.
Solid phase microextraction associated with microwave assisted extraction of food products
Authors: Wang Yuwen , Bonilla Marisa , McNair Harold M. , Khaled Maha 
Published: May 2005

AbstractVeltol® (2‐methyl 3‐hydroxy 4‐pyrone) and Veltol‐Plus® (2‐ethyl 3‐hydroxy 4‐pyrone) are patented flavor ingredients in food products. Only Veltol® can occur naturally, but both Veltol® and Veltol‐Plus® are often added to food products. In order to monitor the use of these compounds in food products, lower detection limits were needed. The Solid Phase Microextraction (SPME) technique for beverages and SPME coupled with Microwave Assisted Extraction (MAE) for solid food samples were studied. The influence of the pH, salt content, SPME adsorption time, GC inlet conditions, and the conditioning of the SPME fiber were investigated. Different food products were tested including coffee, beverages, chewing gums and potato chips. The coupled MAE and SPME shows good results for solid food samples. The reproducibility of the technique was less than 13%RSD and the detection limit was 10 ppb for Veltol® and 2 ppb for Veltol‐Plus® using the SIM mode in GC/MS. The technique also shows good selectivity for the target compounds investigated in different food samples.
Determination of organochlorine compounds in fatty matrices: Application of normal‐phase LC clean‐up coupled on‐line to GC/ECD
Authors: van der Hoff G. René , Baumamn Robert A. , van Zoonen Piet , Brinkman Udo A. Th. 
Published: May 2005

AbstractOff‐line normal‐phase LC has been used for the clean‐up of compounds in our laboratory for several years. On‐line coupling of this LC system, which typically yields 12 ml fractions, is not possible due to its large fraction volume. The maximum transfer volume in on‐line LC‐GC/ECD is approx. 300 μl. Therefore down‐scaling of the LC system was attempted in order to reach these low fraction volumes. Miniaturization resulted in a 240 μ1 LC fraction containing the analytes of interest, which is transferred to GC/ECD via an on‐column interface. Sensitivity requires that a minimum amount equivalent to 1–2 mg of sample should reach the GC detector; the selectivity is determined by the separation between the matrix and the last eluting target analyte.For the analysis of fatty samples, limitations were observed in the separation of dieldrin from triglycerides. Other organochlorine compounds, e.g. polychlorobiphenyls (PCBs), the DDT group, HCB and the HCHs can be analyzed with RSDs of 2–4 % (n = 10) at concentration levels of sub‐μ/kg in milk fat using a 3 μm Hypersil silica 50 × 1.0 mm i.d. LC column.
Ion chromatographic determination of salicylate in human serum with a bulk acoustic wave sensor as detector
Authors: Bing‐Sheng Yu , Li‐Hua Nie , Shou‐Zhuo Tao 
Published: May 2005

AbstractSalicylate is a hydrolysis product of salicylate‐containing drugs (such as aspirin) in patients' blood. Monitoring of this ion in blood is helpful for diagnosing of overdosage of these drugs. The present paper describes an ion chromatography (IC) method developed for determination of total salicylate in human serum, in which a hulk acoustic wave (BAW) sensor was used as detector; 0.5 mmoI/L sodium carbonate (Na2CO3, pH 8.5) served as mobile phase. Interference in the determination was negligible. The method is simple, rapid, accurate, and precise. Serum salicylate was analyzed using both the proposed IC‐BAW method and the classical Trinder spec‐trophotometric method, and the results showed that the two method agreed well.
Stereoisomeric flavor compounds LXXVII: 3‐Butylhexahydrophthalides: Simultaneous enantioselective analysis, structure elucidation, and sensorial properties of the stereoisomers
Authors: Bartschat Dietmar , Wüst Matthias , Mosandl Armin , Hanssum Helmut 
Published: May 2005

AbstractUsing heptakis‐(2,3‐di‐O‐acetyl‐6‐O‐tert‐butyldimethylsilyl)‐β‐cy‐clodextrin as the chirul stationary phase in enantioselective gas chromatography, the simultaneous enantioselective analysis of all eight 3‐butylhexahydrophthalide Stereoisomers was achieved. Fur‐thermore, the odor characteristics and odor thresholds were investigated by enantioselective gas chromatography/olfactometry. Racemic standards were synthesized via hydrogenation and subsequent base catalyzed epimerization. Starting from racemic 3‐butylphthalide. After separation by high performance liquid chromatography. Relative configurations of the pure diastereoisom‐ers were determined by means of NOE‐difference spectroscopy. The absolute configuration at C‐3 was determined starting from (3S)‐butylphthalide as an educt for hydrogenation and epimerization. Absolute configurations of all eight 3‐butylhexahydrophtbalide stereoisomers are unambiguously concluded from the NOE‐experi‐ments in connection with the determination of the absolute configuration at C‐3.
Enantiomeric composition of the chiral constituents of essential oils—part 3: Diterpene hydrocarbons
Authors: Pietsch Martin , König Wilfried A. 
Published: May 2005

AbstractEnantiomeric diterpene hydrocarbons were isolated from different plants and identified by mass spectrometric and NMR investigations. All enantiomeric pairs could be resolved by capillary gas chromatography using either heptakis(2,6‐di‐O‐methyl‐3‐O‐pen‐tyl)‐β‐cyclodextrin or heptakis(6‐O‐tert‐butyldimethylsilyl‐2,3‐di‐O‐methyl)‐β‐cyclodextrin as chiral stationary phases.
Differentiation of strawberry varieties through purge‐and‐trap HRGC‐MS, HRGC‐FTIR and principal component analysis
Authors: da Silva Marco D. R. Gomes , das Neves Higuinaldo J. Chaves 
Published: May 2005

AbstractThe aroma composition of three different Fragaria anannassa cul‐tivars Selva, Chandler, and Osso Grande) is studied by purge‐and‐trap HRGC and the components identified by MRGC‐MS and HRGC‐FTIR. The chromatographic aroma profiles from four different maturation stages in each variety are compared and the similarities accessed by principal component analysis (PCA). The contents in n‐hexanal and hex‐2(Z)‐enal are characteristic features of the green stage in the three varieties where the content differences in methyl, ethyl, and butyl acetates act as typifying variables among varieties. Ethyl acetate acts as an important differentiation variable for the Selva variety. In the mature stage, the three cultivars may be distinguished from each other through their relative contents of methyl and ethyl 2‐methylbutyrate (Selva), methyl 2‐methyl‐butyrate, methyl butyrate (Chandler), methyl and ethyl butyrates, and methyl caproate (Osso Grande).
Analysis of individual natural pyrethrins in indoor matrices by HRGC/ECD
Authors: Berger‐Preiß Edith , Levsen Karsten , Preiß Alfred 
Published: May 2005

AbstractAn HRGC/ECD method is presented which permits the identification and quantitation of individual components of pyrethrins (cinerin I, jasmolin I, pyrethrin I, cinerin II, jasmolin II, pyrethrin II) in indoor matrices (airborne particles, house dust) after application of an agent containing pyrethrum. In order to prepare calibration standards for the individual components of the pyrethrum extract, the pyrethrins were isolated hy semi‐preparative HPLC and their content and purity were determined by 1H‐NMR spectroscopy.
A novel system for purge‐and‐trap with thermal desorption: Optimization using tomato juice volatile compounds
Authors: Sucan Mathias K. , Russell Gerald F. 
Published: May 2005

AbstractA system for purge‐and ‐trap with thermal desorption was developed and optimized to moniotor aroma compounds at ambient temperatures. Canned tomato juice volatiles were used as a model system to develop and evaluate the method. Volatile components were first adsorbed on insert‐traps packed with Tenax‐TA polymer, then thermally desorbed directly inside a gas chromatograph injector. Volatile matgerials occuring in Very low amounts could be entrained and subsequently chrfomatographed, with sensitivity limited by the purity of the sweep gas. Quantitative measurement of tomato juice volatiles was linear with sample size upn to 100 gram samples. The amount of trapped volatiles was proportional to trapping time; howver, low‐and intermediate‐boilers broke through the trap after one hour while high‐boilers continued to be retained. Apurge gas flow rate of 20ml/min gave optimum results mediate‐biolers. Optimum recovery of volatile compounds was obtained with a desorption temperature of 200°c for 5 min. Coefficients of variation from triplicate runs were relatively small. The method showed promise for a simple, sensitive, and reproducibel flavor volatiles collection system for the accurate analysis of tomato compounds.