bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultratrace determination of 1,2,4‐trichlorobenzene in waste water by purge and trap/gas chromatography coupled to different detectors: Flame ionization (FID), electron capture (ECD), and multiple ion detection‐mass spectrometry (MID‐MS)
Authors: Borrelli Raffaella , Fiorani Tiziana , Golfetto Piero
Published: May 2005

High resolution gas chromatography (HRGC) coupled to a “purge and trap” extraction‐injection technique is described as a method of determining 1,2,4‐trichlorobenzene in water at levels as low as parts‐per‐trillion (ppt). In order to investigate the interference from other volatile organic compounds (VOCs) several detection systems were compared: flame ionization, electron capture, and mass spectrometry‐multiple ion detection. Concentrations ranging from 15 to 600 ng/L were analyzed in 20 ml standard aqueous solutions. The mean accuracy of the method varied from 89 to 103%, and its mean precision varied from ± 0.85 to ± 7.5 % for all detectors. The detection limits were 20 ng/L for FID, 2 ng/L for ECD and 0.5 ng/L for MID‐MS detectors. The procedure was successfully applied to the analysis of industrial waste waters. The necessity of an appropriate internal standard to improve the quantitative determination and to determine possible losses or degradation of 1,2,4‐trichlorobenzene during handling or storage is discussed.
Relative velocity profile and flow‐rate in sedimentation field‐flow fractionation
Authors: Martin Michel
Published: May 2005

Although the classical retention theory is used for interpreting data or optimizing separations in sedimentation field‐flow fractionation (SedFFF), as in most other field‐flow fractionation techniques, the assumption of a parabolic flow profile on which this theory is based is not rigorously correct in SedFFF because of the curvature of the channel walls. In order to examine quantitatively the influence of this effect, the relative velocity profile in SedFFF is obtained by solving the Navier‐Stokes equation in cylindrical coordinates. Discrepancies found in the literature about the definition of the mean velocity in such channels are discussed. Relationships between mean velocity, flow‐rate and pressure gradient are given.

Approximating the velocity profile by a third‐degree polynomial of the radial coordinate which provides the same slope as the exact profile at a reference wall, for small values of δ, the curvature ratio (ratio of the channel thickness to the mean curvature radius), shows that the adjustable parameter of the approximate profile, ν, is equal to ± δ/3, the sign depending on whether the reference wall is the inner or outer wall. The curvature ratio appears to be a good indicator of the error made on retention when using the straight channel approximation in retention theory. The error is quite small for typical SedFFF channels. It may have to be taken into account for precise determinations if thicker channels and/or miniaturized systems are used.
Shifting of gas chromatographic retention times due to solvent effects — a study using sulfur chemiluminescence detection
Authors: Dietz Edward A.
Published: May 2005

Gas 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

In 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

Determination 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

Carbohydrates 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

By 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

Normal‐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

A 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

The 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

Recent 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

Four 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

Several 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

The 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

In 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

Splitless 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

Veltol® (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

Off‐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

Salicylate 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

Using 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

Enantiomeric 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

The 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

An 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

A 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.
Determination of the alcohol denaturants denatonium benzoate (bitrex) and diethyl phthalate by direct flow injection APCI‐MS analysis
Authors: Alvarez‐Piñeiro Ma Elena , De Alda‐Villaizán Ma Joséa López , Paseiro‐Losada Perfecto , Lage‐Yusty Ma Asunción
Published: May 2005

The recently developed tandem technique, mass spectroscopy with atmospheric‐pressure chemical ionization (APCI‐MS) coupled with direct flow injection, was applied to the determination of Bitrex (denatonium benzoate) and diethyl phthalate in ethanol. The compounds were indentified from their total‐ion chromatograms(m/z 50‐500) and, simultancously, quantified using selected‐ion chromatograms recorded at m/z 223 for diethyl phthalate and m/z 325 for Bitrex. Operating conditions were optimized for soft ionization (positive ion‐mode) with fragmentation limited to that necessary for analyte identification, which was by the external‐standard method. Calibration curves were rectilinear in the concentration rages 2‐30 μg ml−1 (Bitrex) and 0.075‐1.2% v/v (diethyl phthalate); measurement precision (RSDs were 11.48% for Bitrex and 2.22% for diethyl phthalate), and detection limits (0.017 μg ml−1 and 0.010% v/v, respectively) were adequate for simiultaneous quantitation and with high sensitivity. The lack of any sample pretreatment and the use of flow‐injection analysis meant that the procedure was moere straightforward and rapid than previously reported methods.
Pressure effects on relative retention in capillary gas‐liquid chromatography
Authors: Berezkin Victor G. , Korolev Alexander A. , Malyukova Irina V.
Published: May 2005

Equations have been obtained for the dependence of relative retention and retention indexes on average column pressure. The equations suggested conform well with experimental data. It was shown that limiting value of relative retention (at the pressure approaches zero) is an invariant retention value. The nature of the stationary liquid phase used and its film thickness have a substantial influence on the dependence of relative retention and capacity factor on the pressure.
Analytical approach in diagnosis of inherited metabolic diseases: Maple syrup urine disease (MSUD) – simultaneous analysis of metabolites in urine by enantioselective multidimensional capillary gas chromatography‐mass spectrometry (enantio‐MDGC‐MS)
Authors: Podebrad Frank , Heil Martin , Leib Saandra , Geier Bernhard , Beck Thomas , Mosandl Armin , Sewell Adrian C. , Böhles Hans
Published: May 2005

Maple Syrup Urine disease (USUD) is an autosomal recessive inherited metabolic disorder of branched‐chain amino acid (L‐valin, L‐leucine, and L‐isoleucine metabolism named after the characteristic smell of affected patients urine. MSUD is caused by a deficiency of the branched‐chain α‐keto acid dehydrogenase compex resulting in an accumulation of branched‐chain aamino acids and the corresponding α‐keto‐and α‐hydroxy acids in blood, urine and cerebrospinal fluid causing neurological damage and mental retardation. The enantioselective analysis of chiral MSUD metabolites and analysis of achiral compounds as corresponding N,O‐methoxycarbonyl methyl esters by derivatization with methyl chloroformate (MCF) has been achieved simultaneusly by enantioselective multidimensional gas chromatography‐mass spectrometry using heptakis (2,3‐di‐O‐methyl‐6‐O‐tert‐butyl‐dimethyl‐silyl)‐β‐cyclodextrin as chiral stationary phase. Derivatization with MCF allows the analysis of the structurally different metabolitetes such as branched‐chain‐carboxylic‐, α‐oxo‐, α‐hydroxy‐ and α‐amino acids in a single chromaatographic run. Mass selective detection immensely improves the unequivocaaal identification of metabolites even when they occur as trace compound. The described method allows a reliable screening of MSUD metabolites in patients' urine without time consuming sample preparation and is also suitable for label enrichment analysis without any methodical changes. During this investigation urine sample from three MSUD paatients were analyzed.
Automated derivatization for on‐line solid‐phase extraction‐gas chromatography; phenolic compounds
Authors: Louter Arjan J. H. , Jones Philo A. , Jorritsma J. David , Vreuls Jolan J. , Brinkman Udo A. Th.
Published: May 2005

An automated system for derivaatization was coupled on‐line with solid‐phase extraction‐gas‐chromatography (SPE‐GC). The system was optimized for the determination of phenol and chlorinated phenols in aqueous samples. The test analytes were acetylated with acetic anhydride; proper buffering of the sample was a critical factor. Next, the phenol acetates were enriched on a SPE cartridge and transferred to a GC; two appraoaches were studied. In the first approach, the derivatives were enriched on disposable C18 cartridges (ASPEC type) and desorbed with methylacetate. Aan aliquot of the final eluate was injected on‐line the GC by means of a loop‐type interface. In the second approach, trace enrichment was performed on 10 × 2 mm i.d. LC‐type precolumn packed with polystyrenedivinylbenzene copolymer (PLRP‐S) this precolumn was dried with a mitrogen purge and the phenol acetates were desorbed with ethyl acetate which was injectedon‐line into the retention gap of the GC under partially concurrent solvent evaporation (PCSE) conditions. The Derivatization‐SPE‐GC system which was based on the loop‐type interface has the advantage of simplicity and easy operation, the main drawback is the impossibility to determine phenol acetates which elute prior to trichlorophenol acetates. With the derivatization‐SPE‐GC approach using PCSE‐based desorption, even the most volatile analyte of the test series, phenol acetate, can be determined successfully. The entire procedure, including the derivatization step, was fully automated and integrated in one set‐up. The precision data for the integrated on‐line derivatization‐SP‐FID system were fully satisfactory, with RSD values of 1–12 % at the 1 μg/1 level. When a sample volume of 2.2 ml was analyzed, The detection limits for the chlorinated phenol acetates were in the 0.1–0.3 μg/1 range.
Starburst dendrimer‐supported pseudostationary phases for electrokinetic chromatography
Authors: Tanaka Nobuo , Iwasaki Hironobu , Fukutome Takeshi , Hosoya Ken , Araki Takeo
Published: May 2005

Pseudo‐stationary phases for electrokinetic chromatography were prepared by the alkylation of starburst dendrimers (SBDs). The SBD‐supported pseudo‐stationary phase with dodecyl groups showed higher efficiency than short‐akyl derivatives, and maintained the hydrophobic property inthe presence of methanol. The dodecyl‐modified SBD provided wide migration time windows ar high methanol content to effect the separation of sixteen aromatic hydrocarbons, the priority pollutants designated by EPA, in 65% methanol. The selectivity of polymer‐supported pseudo‐stationary phase can be varied simply by changing the length of the alkyl groups. The dodecyl SBD showed relatively similar selectivity as sodium dodecyl culfate micelle, whereas short alkyl derivatives showed preference towards rigid and planar compounds based on the rigid and planar compounds based on the rigid polymer backbones. The selectivity of SBD‐supported pseudo‐stationary phases was dominated by the chain length of the alkyl groups, with the minor effect of the structure of the core and the generation of SBD where alkyl groups were attached.
Supercritical fluid extraction of kava lactones from Piper methysticum (kava) herb
Authors: Lopez‐Aila Viorica , Benedicto Janet
Published: May 2005

Supercritical fluid extraction of kava lactones from Piper methysticum Forst. herb is described here. The extraction was performed with supercritical carbon dioxide alone and supercritical carbon dioxide modified with 15% ethanol, and the extracts were analyzed by gas chromatography/mass spectrometry. Seven lactones including: 7,8‐dihydrokavain; kavain; 5,6‐dehydrokavain; 5, 6, 7, 8‐tetrahydroyangonin; dihydromethysticin; yangonin; and methysticin were the major constituents in the SFE extract.
Chemical characterization of ozonated lignin solutions from corn (Zea mays) stalk and poplar (Populus deltoides) wood by capillary gas chromatography
Authors: Quesada Joaquín , Rubio Manual , Góamez Demetrio
Published: May 2005

Corn (Zea mays) stalk and poplar (Populus deltoides) wood lignin was converted into monomeric aromatic compounds and short chain aliphatic carboxylic acids. The main reaction products were separated and identified using capillary gas chromatography‐mass spectrometry on an HP‐5 column. The compounds were considered as positively identified when their mass spectra and GC retention times agreed with those of authentic standard samples. The quantitative estimation of the identified reaction products was accomplished on an OV‐101 capillary column by gas chromatography‐FID using the internal standard method. Among the aromatic compounds, aldehydes (p‐hydroxybenzaldehyde, vanillin, and syringaldehyde), acids (p‐hydroxybenzoic, vanillic, 3,4‐dihydroxybenzoic, and syringic), and one phenol (hydroquinone) were determined. In addition, the aliphatic carboxylic acids: glycolic, oxalic, malonic, glyoxylic, butanedioic, glyceric, and malic acid were identified. All the calibration curves of the quantified compounds approximated to a straight line. For both corn stalk and poplar wood lignins, the major components were the aromatic aldehydes (71 and 64% of the characterized fraction, respectively), followed by the aliphatic carboxylic acids (20 and 21% of the characterized fraction, respectively).
Determination of acylglycerols in vegetable oil methyl esters by on‐line normal phase LC‐GC
Authors: Lechner Marion , Bauer‐Plank Christina , Lorbeer Eberhard
Published: May 2005

An on‐line LC‐GC method for the analysis of mono‐, di‐, and triacylglycerols in vegetable oil methyl esters has been developed. The concentrations of these components have turned out to be key parameters for the quality of diesel fuel substitutes. Separation of all classes of acylglycerols from the fatty acid methyl ester matrix is achieved by LC after acetylation of the hydroxyl groups. The acylglycerol fraction is transferred on‐line to GC, using the loop‐type interface and concurrent eluent evaporation. Quantification of mono‐, di‐, and triacylglycerols is performed by combining external calibration with internal standardization. Both recovery of the procedure and reproducibility of the quantitative results are evaluated.
Capillary gas chromatographic separation of C10–C12 secondary phenylalkanes on modified cyclodextrin stationary phases
Authors: Špáanik Ivan , Krupcik Jáan , Skacáani Ivan , De Zeeuw Jaap , Galli Mario , Sandra Pat
Published: May 2005

The separation of isomers and enantiomers of branched C10‐C12 phenylalkanes by gas chromatography on fused silica capillary columns coated with some modified β‐ and γ‐cyclodextrins was studied. It was shown that the separation of positional isomers of C10‐C12 phynylalkanes on modified cyclodextrin capillary columns is not better than that on a column coated with modified polyethylene glycol. Differences were found in the enantioselectivity of modified β‐ and γ‐cyclodextrins for the separation of C10‐C12 secondary phenylalkane enantiomers. While alkylderivatives of β‐CDs resolve enantiomers of 3‐phenylalkanes, alkyl derivatives of γ‐CD resolve enantiomers of 2‐phenylalkanes. Since shape selectivity factors of modified cyclodextrins have indicated no inclusion of the considered solutes in cyclodextrin cavities, enantioselective interactions most probably occur on the outer sphere of cyclodextrins.
Truncation of the ectodomain of the human insulin receptor results in secretion of a soluble insulin binding protein from transfected CHO cells
Authors: Ellis Leland , Sissom Janice , Levitan Alla
Published: May 2005

The Insulin receptor is an integral transmembrane glycoprotein comprised of two α‐(∼ 135kDa) and two β‐(∼ 95kDa) subunits, which is synthesized as a single polypeptide chain precursor (αβ). The primary sequence of the human insulin receptor (hIR) protein, deduced from the nucleotide sequence of cloned human placental mRNAs, predicts two large domains (929 and 403 residues) on either side of a single membrane spanning domain (23 residues); each of these major domains has a distinct function (insulin binding and protein/tyrosine kinase activity, respectively). To experimentally test this deduced topology, and to explore the potential for independent domain function by the hIR extracellular domain, we have constructed an expression plasmid encoding an hIR deletion mutant which is truncated 8 residues from the beginning of the predicted transmembrane domain (i.e., 921 residues). This domain of the hIR is in fact processed into α‐and truncated β‐subunits and secreted with high efficiency from transfected CHO cell lines which express this mutant hIR, and the protein accumulates as an (αβ)2 dimer in the medium. This molecule is recognized by a battery of 13 monoclonal antibodies to epitopes on the IR extracellular domain, four of which block insulin binding and two of which require the native conformation of the IR for recognition. Further, this domain, binds insulin with an apparent dissociation constant comparable to that of the wild‐type hIR. However, the secreted dimmer displays a linear Scatchard plot, while that of the wild‐type membrane‐associated hIR curvilinear. These results, together with previous results with a soluble derivative of the hIR cytoplasmic protein/tyrosine kinase domain, are consistent with the deduced topology. The IR is indeed comprised of two large soluble domains connected by a single membrane spanning domain, which on the one hand act concert upon ligand binding (insulin‐dependent activation of the protein/tyrosine kinase) to initiate the insulin response in cells, but on the other hand are each capable of autonomous function (ligand binding and protein/tyrosine kinase activity, respectively).
The design and synthesis of mimetics of peptide β‐turns
Authors: Kahn Michael , Wilke Susanne , Chen Barbara , Fujita Kagari , Lee Yu‐Hwei , Johnson Michael E.
Published: May 2005

The synthesis of an 11 membered ring bis‐lactam, a system which is designed as a conformationally restricted mimetic of type I and II β‐turns is described. Computer assisted molecular modeling was used to compare the predicted low energy conformers of the turn mimetic with idealized type I and type II turn structures. Initial computation analysis indicates that the basic ring structure will provide an excellent foundation for the development of variety of β‐turn mimetics.
Anhydroelastase: Enhanced affinity toward product‐type ligands revealed by affinity chromatography
Authors: Kumazaki Takashi , Kobayashi Masatomo , Ishii Shin‐ichi
Published: May 2005

Anhydroelastase was effectively isolated by a single operation of affinity chromatography from a complex mixture produced by phenylmethylsulfonylation and alkaline treatment of porcine pancreatic elastase. The adsorbent used for the chromatography was 6‐aminohexanoyl‐trialanine, which corresponds to a product of elastase action, immobilized on Sepharose 4B. Successful resolution by the operation indicated that this immobilized ligand possesses the highest affinity for anhydroelastase among various proteins including regenerated elastase in the mixture. Comparative affinity chromatography on immobilized anhydroelastase and on immobilized native elastase further confirmed the stronger interaction of anhydroelastase with the product‐type peptides. Immobilized anhydroelastase was also found to be useful in the purification and search for naturally occurring proteinase inhibitors.
Contribution of antigen processing to the recognition of a synthetic peptide antigen by specific T cell hybridomas
Authors: Boyer Michel , Novak Zuzana , Fotedar Arun , Singh Bhagirath
Published: May 2005

Most antigens recognized by T cells require unfolding or partial degradation (processing) followed by association with Major Histocompatibility Complex (MHC) molecules. We examined the processing requirements for the presentation of antigen to two T cell hybridomas which recognize the α‐helical synthetic polypeptide antigen Poly 18, Poly [EYK(EYA)5], in association with I‐Ad. Hybridoma A.1.1 responds to EYK(EYA)4 as the minimum antigenic sequence while hybridoma B.1.1 recognizes (EYA)5 sequence. It was found that these hybridomas responded to Poly 18 and to minimum peptide sequences presented by glutaraldehyde and chloroquine treated antigen presenting cells (APC), suggesting that antigen processing is not a requirement for the activation of these cells. The reactivity pattern of hybridoma B.1.1 in the presence of glutaraldehyde fixed APC revealed that antigens containing lysine were presented with much less efficiency than antigens without lysine, suggesting an interaction of these residues with the antigen presenting cell surface. We discuss the possibility that alanine residues in the α‐helical Poly 18 form a hydrophobic ridge which may be required for appropriate interaction between antigen, the T cell receptor, and MHC molecules.
Transition of environmental polarity of tyrosine‐76 of Trimeresurus flavoviridis phospholipase A2 upon active site ligand binding
Authors: Sakai Hironori , Oda Naoko , Kohzuma Takushi , Liu Song‐Yuan , Ohno Motonori , Kihara Hiroshi
Published: May 2005

Modification of Trmeresurus flavoviridis phospholipase A2 with a 5‐fold molar excess of tetranitromethane produced 40% active mononitrotyrosyl phospholipase A2 in which Try‐76 was specifically nitrated. This is in contrast to the case of mammalian pancreatic phospholipases A2 where Tyr‐70 but not Tyr‐76 was nitrated. When Ca2+ was bound to T. flavoviridis mononitrotyrosyl phospholipase A2, nitrated tyrosine (Tyr)NO2‐76 moved from a less polar site to a polar site with the decrease of the pKa value of its hydroxyl group. Nitration of Tyr‐76 did not influence the binding affinity to Ca2+. Addition of laurylphosphorylcholine to mononitrotyrosyl phospholipase A2 in the presence of Ca2+ caused the movement of Try(NO2)‐76 from a polar environment to a less polar environment with the rise in the pKa value. Tyrosine‐76 is located in the site whose environmental polarity is affected by the binding of the ligands to the active site. As Tyr‐76 is located in the site not proximal to the active site, it could be assumed that the conformational change induced by the binding of the ligands extends to the region remote from the active site in T. flavoviridis phospholipase A2. This might provide evidence of long‐range diffusional coupling between remote sites in the noncooperative globular protein.
A subsequence‐specific DNA‐binding domain resides in the 13 kDa amino terminus of the bacteriophage Mu transposase protein
Authors: Tolias Peter P. , DuBow Michael S.
Published: May 2005

We have previously reported that the 13kDa amino terminus of the 70 kDa bacteriophage D108 transposase protein (A gene product) contains a two‐component, sequence‐specific DNA‐binding domain which specifically binds to the related bacteriophage Mu's right end (attR) in vitro. To extend these studies, we examined the ability of the 13 kDa amino terminus of the Mu transposase protein to bind specifically to Mu attR in crude extracts. Here we report that the Mu transposase protein also contains a Mu attR specific DNA‐binding domain, located in a putative α‐heix‐turn‐α‐helix region, in the amino terminal 13 kDa portion of the 70 kDa transposase protein as part of a 23 kDa fusion protein with β‐lactamase. We purified for this attR‐specific DNA‐binding activety and ultimately obtained a single polypeptide of the predicated molecular weight for the A′—′bla fusion protein. We found that the pure protein bound to Mu attR site in a different mannar compared with the entrie Mu tranposase protein as determined by DNase I‐footpriting. Our results may suggest the presence of a potential of a potential primordial DNA‐binding site (5′‐PuCGAAA‐3′) located several times within attR, at the ends of Mu and D108 DNA, and at the extremities of other prokaryotic class II elements that catalyze 5 base pair duplications at the site of element insertion. The dissection of the functional domains of the related phage Mu and D108 transposase provide clues to the mechanism and evolution of DNA transposition as a mode of mobile gentic element propagation.
The conformation of core oligosaccharides from Escherichia coli and Salmonella typhimurium lipopolysaccharides as predicted by semi‐empirical calculations
Authors: Jansson Per‐Erik , Wollin Ralfh , Bruse Gert W. , Lindberg Alf A.
Published: May 2005

The preferred conformation of the hexose and heptose regions of core saccharides from Enterobacteriaceae lipopolysaccharides was calculated. The Hard Sphere Exo Anomeric (HSEA) approach was used and the minimum energy conformation of the Salmonella typhimurium and Escherichia coli R1, R2, R3, R4 and K12 cores calculated. The results indicate that most of the cores are sterically crowded, with small degrees of freedom, and that the hexose and heptose parts from two separate regions. The core structures exhibit a ‘front’‐side and a ‘back’‐side, the former being similar for all the structures and latter being characteristic for each core type.
Definition of the phage G13 receptor as structural domains of trisaccharides in Salmonella and Escherichia coli core oligosaccharides
Authors: Wollin Ralfh , Bruse Gert W. , Jansson Per‐Erik , Lindberg Alf A.
Published: May 2005

The interaction between phage G13 and different bacterial and synthetic oligosaccharides has been studied using equilibrium dialysis inhibition. The results, and conformational analysis of the oligosaccharides, make us conclude that the phage G13 carbohydrate receptor is a conformational domain involving three sugar residues. The following trisaccharide elements contain in domain: α‐D‐Galp‐(1→3)‐[α‐D‐Galp‐(1→6)]‐α‐D‐Glcp, α‐D‐Manp‐(1→3)‐[α‐D‐Manp‐(1→6)]‐α‐D‐Manp, and α‐D‐Glcp‐(1→3)‐[L‐gly‐α‐D‐man‐Hepp‐(1→7)]‐L‐gly‐α‐D‐man‐Hepp. Thus two structures, either a hexose substituted with α‐D‐glycopyranosyl groups in the 3‐ and 6‐positions, or a heptose substituted with such groups in the 3‐ and 7‐positions are functional G13 binding sites. Such domains are present in several cores of lipopolysaccharides from Salmonella and Escherichia coli species. Some cores, e.g. those from S. typhimurium chemotypes Ra, Rb1 and Rb2, contain two such domains. The identification of two G13 receptor domains within different core saccharides could explain the broad host range this phage.