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  • Analytical Chemistry and Spectroscopy  (25,705)
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  • 1
    ISSN: 0935-6304
    Keywords: SPME ; desorption ; fiber conditioning ; field sampling ; sample preparation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract
    Additional Material: 3 Ill.
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  • 2
    ISSN: 0935-6304
    Keywords: Open tubular columns ; capillary electrochromatography ; column efficiency ; injected volume ; applied voltage ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of some instrumental parameters on column efficiency in open tubular capillary electrochromatography (OTCEC) has been evaluated. First, it was investigated whether band broadening due to the sample injection process is within a tolerable range when an open tubular column (OTC) of about 10 μm i. d. is used. As a result of the small injection profile factor (K2 = 1.3), injected volumes must be sufficiently small (less than 10 pL) to avoid a significant efficiency loss (〉5%) when hydrodynamic injection by siphoning is employed. Secondly, the kinetic performance of OTCs in a CEC system was estimated from the variation of the reduced plate height (h) with the reduced linear velocity (ν) which was controlled by the voltage applied. Reasonable agreement was obtained between the theoretical h versus ν curve and the experimental values for a group of polycyclic aromatic hydrocarbons used as test compounds. Values of 0.25 for minimum h at an optimum ν of 16 are estimated, which permit separations with around 400,000 plates per meter to be obtained in less than 5 min. Finally, the possibility of estimating the diffusion coefficients of the solutes in the mobile phase from the plot of the height of a theoretical plate versus electroosmotic flow velocity is shown.
    Additional Material: 5 Ill.
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  • 3
    ISSN: 0935-6304
    Keywords: Speciation ; digestion ; capillary electrophoresis ; ferrous ; ferric ; mineral analysis ; complexation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Capillary electrophoresis is used as a means of cation separation for cationic speciation analysis. Acceptable separation of ferrous and ferric iron was achieved by using a mixed complexing agent run buffer which gave stable species in solution. These iron species, and total iron, were determined simultaneously in certified reference materials with a single digestion step. A variety of digestion techniques were compared, primarily for their non-oxidative capabilities in order to preserve the oxidation state of iron in the mineral samples. The most favorable recoveries resulted from a continuous flow nitrogen purge technique. Total iron levels obtained from the CE method were compared with those determined by two spectroscopic techniques, with similar results obtained using the different instrumental methods.
    Additional Material: 3 Ill.
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  • 4
    ISSN: 0935-6304
    Keywords: Capillary electrophoresis ; enantiomer separation ; chiral drugs ; TM-γ-cyclodextrin ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---High-throughput screening is a promising new approach in analytical chemistry. Within the framework of an extended screening program (The German-Chinese Drug Screening Program), the enantioseparation of 86 drugs was investigated by capillary zone electrophoresis in the presence of the chiral solvating agent (CSA) octakis-(2,3,6-tri-O-methyl)-γ-cyclodextrin (TM-γ-CD). By this means, 15 drugs could be separated into enantiomeric pairs. Approximate measures for the degree of interaction (migration retardation factor, Rm) and for the degree of enantiomer recognition (migration separation factors, αm) revealed intriguing patterns that were compared with those found for native γ-cyclodextrin (γ-CD). Although there is a distinct influence of the analyte structure on the electrophoretic data, interpretation remains difficult. Most remarkably, permethylation of γ-CD leads neither to a higher affinity nor to better chiral recognition, in contrast to the findings with α-CD.
    Additional Material: 10 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0935-6304
    Keywords: Cyclodextrin ; capillary electrophoresis ; system peak ; CHES 1 ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using a running buffer containing cyclodextrins (CDs) and 2-[N-cyclohexylamino]-ethanesulfonic acid (CHES), positive system peaks were observed in the analysis of a ganglioside mixture by CE-UV. These system peaks were related to CDs in the running buffer because these peaks were also detected when a plug of solution devoid of CDs but having the same CHES concentration and pH as the running buffer was injected. Neutral CDs were separated owing to the formation of inclusion complexes with the anionic CHES ion. One possible explanation for the positive system peaks is that the anionic CD-CHES inclusion complex is displaced by co-ions with higher UV absorptivity.
    Additional Material: 3 Ill.
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  • 6
    ISSN: 0935-6304
    Keywords: O-Aryl,O-(1-methylthioethylideneamino)phosphates ; retention prediction ; quantitative structure-retention relationship (QSRR) ; reversed-phase HPLC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Using factor analysis and stepwise linear regression methods, two parameters - CMR and ECCR - were selected from eight solute-related structure parameters as the most retention-influencing parameters. The relationships between the retention data (k ´) and the two structure parameters were established for 13 O-aryl,O-(1-methylthioethylideneamino)phosphate compounds under a wide range of experimental conditions. The retention data (k ´) of another seven compounds with similar structures were predicted using these QSRR equations. Good agreement was obtained between the experimental k ´ values and predicted ones.
    Additional Material: 1 Ill.
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  • 7
    ISSN: 0935-6304
    Keywords: Capillary isotachophoresis ; capillary electrophoresis ; column-coupling electrophoresis ; enantiomers ; chiral ; amino acids ; tryptophan ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The ability of capillary zone electrophoresis (CZE) coupled on-line with capillary isotachophoresis (ITP) sample pretreatment in the column-coupling capillary electrophoresis equipment to separate trace enantiomers present in samples of complex ionic matrices and enantiomers present in their mixtures at significantly differing concentrations has been studied. Enantiomers of 2,4-dinitrophenyl labeled norleucine (DNP-Nleu) and tryptophan enantiomers were employed as model analytes in this work while urine and mixtures of tryptophan enantiomers of differing concentrations served as model samples. Experiments performed with urine samples spiked with the DNP-Nleu racemate at sub-μmol/L concentrations demonstrated excellent sample pretreatment capabilities of ITP (concentration of the analytes, in-column and post-column sample clean up) when coupled on-line with chiral CZE separations. In the CZE separations of enantiomers present in the samples at trace concentrations the sample pretreatment could be performed in both achiral and chiral ITP electrolyte systems. The use of a chiral electrolyte system was found to be essential in the ITP pretreatment of the samples containing the enantiomers at very differing concentrations. For example, a 2×10-7 mol/L concentration of L-tryptophan could be detected in the CZE separation stage of the ITP-CZE combination in samples containing about a 104 excess of D-tryptophan only when the ITP pretreatment was carried out in the electrolyte system providing the resolution of enantiomers (α-cyclodextrin served for this purpose in the present work). A post-column ITP sample clean up was found effective in enhancing the destacking rate of the trace enantiomer in the CZE stage when the migration configuration of the enantiomers was less favorable (the trace constituent migrating behind the major enantiomer).
    Additional Material: 8 Ill.
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  • 8
    ISSN: 0935-6304
    Keywords: Capillary SFC ; zinc dialkyldithiophosphates ; lubricating oils ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract
    Additional Material: 5 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0935-6304
    Keywords: Supercritical fluid extraction ; capillary GC ; hydrocarbons ; bio-oil ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract
    Additional Material: 3 Ill.
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  • 10
    ISSN: 0935-6304
    Keywords: Clean-up ; aliphatic hydrocarbons ; organochlorine compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---No abstract
    Additional Material: 2 Ill.
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  • 11
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0935-6304
    Keywords: Multidimensional gas chromatography ; comprehensive two-dimensional gas chromatography ; GC×GC ; oxygenates ; MTBE ; reformulated gasoline ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Comprehensive two-dimensional gas chromatography (GC×GC) has been applied to the quantitation of oxygenates in reformulated gasoline. Target oxygenates were C1-C4 alcohols, tert-pentanol, methyl tert-butyl ether (MTBE), diisopropyl ether (DIPE), ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME). These were separated from the gasoline matrix using a volatility-based selectivity in the first chromatographic dimension, followed by a mixed-phase polarity/shape selectivity in the second dimension. The high resolving power of this stationary phase combination completely separated all oxygenates except DIPE, ETBE, and TAME, which exhibited coelution with other nonpolar gasoline components. Oxygenates quantitation was achieved with the use of an internal standard, an FID detector, and calibration curves. Quantitation results are in good agreement with ASTM and EPA standard methods. When coupled with our previous method for BTEX and aromatics, a single GC×GC method can now quantitate MTBE, alcohols, BTEX, and aromatics in a one-hour analysis.
    Additional Material: 1 Ill.
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  • 12
    ISSN: 0935-6304
    Keywords: Comprehensive two-dimensional gas chromatography ; GC×GC ; thermal modulation ; oil analysis ; petroleum analysis ; analysis of middle-distillate oil fractions ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Comprehensive two-dimensional gas chromatography (GC×GC) is an utterly suitable separation technique for the analysis of complex samples, such as oil fractions. Once the two columns and the operating conditions are properly tuned, the technique is able to provide a detailed characterization of such materials. Some considerations applying to the tuning of a GC×GC system for a specific separation are presented and discussed. The authors present a number of different column sets and conditions which allow the separation of a non-aromatic hydrocarbon solvent, a kerosene, the light end of a crude oil, and an olefinic fraction, respectively. The highly structured GC×GC chromatograms, together with chemical knowledge about the samples, provide a much more comprehensive characterization of the samples than hitherto possible.
    Additional Material: 7 Ill.
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  • 13
    ISSN: 0935-6304
    Keywords: Comprehensive two-dimensional gas chromatography ; thermal desorption modulator ; temperature programming ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---In comprehensive two-dimensional gas chromatography, two individual separations are coupled by means of a rotating thermal desorption modulator interface. The injection pulse introduced via the interface onto the second column should be as short as possible. Parameters affecting the modulator operation are studied. In the set-up used in this study, the temperature of the second column can be programmed independently from that of the first column. Optimization of the second-dimension separation to minimize peak broadening and maximize resolution is discussed and an elegant approach to determine second-dimension retention times using a non-constant modulation frequency is demonstrated. The high separation power of the comprehensive system is demonstrated by the analysis of technical and biota samples containing chlorinated biphenyls and toxaphene.
    Additional Material: 7 Ill.
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  • 14
    ISSN: 0935-6304
    Keywords: GC×GC ; comprehensive two-dimensional GC ; thermal modulation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A jet of cool gas is used to locally cool a section of modulator tube in the presence of the stirred oven bath of a GC×GC instrument. Local cooling decouples the temperature of the modulator tube from that of the first dimension column, which was 100 meters long. Overall resolution of the GC×GC experiment was improved as a result. Another consequence of the jet-cooled thermal modulation structure is the elimination of moving parts in the GC oven. By pulsing cold and hot jets of gas onto a modulator tube with solenoid valves, two stage thermal modulation can be obtained without the complexity of moving parts in the vicinity of the capillary columns.
    Additional Material: 1 Ill.
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  • 15
    ISSN: 0935-6304
    Keywords: Comprehensive two-dimensional GC ; GC×GC ; orthogonal chromatography ; GC/MS ; group type separations ; PCBs ; petroleum ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The writer of this review published in 1978 a three-part article on two-dimensional gas chromatography in the first three issues of this journal [1]. The review was written at a time when capillary column GC was still in its infancy. Commercial columns were (essentially) unavailable and sample introduction into capillary columns was done exclusively in the split mode. Two-dimensional separations were explored in only a few laboratories. The limitations of capillary column technology made this exercise rather difficult. The introduction of fused silica capillary columns in the early eighties drastically changed the landscape in which gas chromatography was practiced. It took the chromatographic community just a few years to convert from packed columns to capillary columns. Instrumentation and accessories specifically designed for capillary column use came onto the market. This writer had great hopes that the revolution in capillary column GC would be mirrored in the development of instrumentation for Two-Dimensional Gas Chromatography. This never materialized. On the contrary, tentative steps taken by a few manufacturers and suppliers of chromatographic equipment fizzled out. It was perhaps the introduction of relatively inexpensive and user friendly GC/MS instrumentation, in combination with nearly indestructible fused silica capillary columns that took away the incentive to develop commercially viable Two-Dimensional Gas Chromatography. Much of the thinking went like this: why insist on good chromatography if mass spectrometry can do the job without the need of complete separation. Some progress in the further development of conventional Two-Dimensional Gas Chromatography has certainly been made over the last 20 years but there has not been a great deal of excitement. Applications have also been relatively sparse and they are limited to just a few areas. Science does not remain static and chromatography is no exception. Progress in gas chromatography is driven by new technology and ideas. Substantial improvements in two-dimensional GC were not forthcoming until Phillips and his research group introduced and implemented an entirely new form of Two-Dimensional Gas Chromatography, called comprehensive GC×GC. This breakthrough occurred only in 1991 [2]. It does take some time before scientists change attitudes and habits. There is always a time lag between the introduction of new technology and its general acceptance. The public's attitude toward comprehensive Two-Dimensional Gas Chromatography is probably no exception. The number of scientists who are actively pursuing this new branch of gas chromatography is still very small. It is often a single individual who carries the torch. J.B. Phillips' name is synonymous with comprehensive Two-Dimensional Gas Chromatography. He is not only its inventor and proponent but his fertile mind has initiated research in other related areas. Sadly, he passed aware shortly before this review was written. This contribution is dedicated to his memory.
    Additional Material: 9 Ill.
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  • 16
    ISSN: 0935-6304
    Keywords: GC×GC ; thermal modulation ; comprehensive three-dimensional GC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Comprehensive three-dimensional gas chromatography (GC3) is demonstrated using modified GC×GC apparatus. A new thermal modulation scheme employing a single moving heater to operate two thermal modulators is introduced. Considerations of the bandwidth/resolution tradeoff of GC3 show that high-speed tertiary columns would make GC3 practical, with modest loss of underlying GC×GC peak capacity.
    Additional Material: 3 Ill.
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  • 17
    ISSN: 0935-6304
    Keywords: Spearmint ; peppermint ; GC×GC ; essential oils ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---This paper investigates the separation of moderately complex samples by comprehensive two-dimensional gas chromatography (GC×GC). The analysis of peppermint (Mentha piperita) and spearmint (Mentha spicata) essential oil components, including acetates, alcohols, furans, ketones, sesquiterpenes, and terpenes, was achieved by one-dimensional gas chromatography with quadrupole mass spectrometry detection (GC/MSD) and GC×GC with flame ionization detection. Peppermint essential oil was found to contain 89 identifiable peaks by GC×GC compared to 30 peaks in the GC/MSD chromatogram. Likewise, 68 peaks were found in the GC×GC chromatogram of spearmint (compared to 28 in GC/MSD). Plots of the first dimension versus second dimension retention times provided a fingerprint of the two essential oils, which revealed 52 similar compounds between the two essential oils as opposed to 18 matches by 1D GC.
    Additional Material: 6 Ill.
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  • 18
    ISSN: 0935-6304
    Keywords: LMCS ; cryogenic modulation ; comprehensive gas chromatography ; GC×GC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Comprehensive gas chromatography is the realization of true continuous multidimensional (dual column) gas chromatography. The key requirement in the comprehensive GC experiment is that the second dimension analysis is completed in a rapid time-frame compared to the elution of components in the first dimension, and that the two coupled dimensions represent ‘orthogonal’ analyses towards the analytes to be separated. The former normally necessitates pulsing of contiguous segments of each chromatographic band from the first to the second dimensions. The two dimensions should be in fluid communication. The comprehensive GC×GC experiment passes all the column flow from the first column to the second column, leading to no sample loss, but this also requires a suitable method for time- or zone-compression of the band to be pulsed to the second column. The final pulse should be narrow, and should be delivered to the second column quickly. A simple procedure can achieve this using the cryogenic modulator that has been recently described by this group. The system uses a cryogenic trap which can be moved away from the cooled zone of the column faster than 10 ms. A fast-acting pneumatic ram achieves this performance. The cooled column heats up to the prevailing oven temperature within 10-15 ms. Molecules as volatile as C5 alkanes or small aromatics will be fully retained by the trap within the period of modulation used for GC×GC. The technique is simple to implement and requires no special column connections. Using a gas chromatograph which allows control of external events and can acquire from a detector at 50 Hz or faster, and a timing controller for modulation, the comprehensive result can easily and effectively be achieved.
    Additional Material: 7 Ill.
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  • 19
    ISSN: 0935-6304
    Keywords: Comprehensive gas chromatography ; cryogenic modulation ; semi-volatile aromatics ; thermal sweeper ; peak widths ; peak asymmetries ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The two current technologies for achieving comprehensive gas chromatography (GC×GC) - the thermal sweeper and the cryogenic modulator - are compared in an interlaboratory study using a multicomponent semi-volatile aromatic compound sample. The same column set (phases, film thickness, dimensions of columns) and conditions of oven temperature program were used. Carrier gas flow settings however were different for the data reported here. The thermal sweeper has a longer overall length due to the extra ca. 30 cm length of narrow bore tubing used for the modulator/accumulator section. Data reveal that the two methods behave in an analogous manner in respect of delivering GC×GC results, with key peak parameters of peak widths and symmetry measures showing good correlation. Retention time dissimilarity on the first dimension columns in the two systems arises from different flow rates used, however the second column retention is similar, and this is due to the resulting different elution temperatures that peaks elute on the first dimension in each system. Overall, the two approaches to GC×GC appear to produce equivalent results within the scope of the application studied. Each system does have its experimental limitations; the thermal sweeper has what may be called a ‘thick film effect’, where at high temperature it can be difficult to sufficiently trap the migrating bands in the accumulator column, and the pulsing of solutes in the cryogenic system may suffer from a ‘thick wall effect’ if a column with too thick a wall dimension is used at low oven temperature.
    Additional Material: 4 Ill.
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  • 20
    ISSN: 0935-6304
    Keywords: Packed capillary liquid chromatography ; temperature programming ; Fourier-transform infrared spectroscopy ; polymer additives ; pneumatic nebulization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Temperature-programmed packed capillary liquid chromatography has been coupled off-line to Fourier-transform infrared spectroscopy, utilizing a commercially available interface with a pneumatic nebulizer rebuilt to handle low flow rates at elevated temperatures. The modified interface showed excellent performance with regard to non-aqueous reversed phase separations of polymer additives, resulting in constructed Gram-Schmidt chromatograms comparable to chromatograms obtained using UV detection. The spray of the in-house constructed nebulizer was not influenced by temperature changes of the column effluent, and hence temperature-programmed gradient separations could be used successfully. The relative standard deviation of peak height was 4.4% (n = 5) and the mass limit of detection was determined to be about 40 ng, using a polymer antioxidant as model compound. The present instrumental coupling has been used for characterization of the antioxidant Irgafos P-EPQ.
    Additional Material: 5 Ill.
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  • 21
    ISSN: 0935-6304
    Keywords: Denuders ; isolation and enrichment ; analysis ; volatile organic compounds ; partition coefficients Kfs ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The possibility of using a piece of gas chromatographic capillary column as a tubular denuder for isolation and enrichment of organic pollutants present in air was studied. The partition coefficients (Kfs) of typical organic pollutants (benzene, chlorobenzene, toluene) between the gaseous phase and the denuder sorption layer were determined and effects of analyte concentration in the gaseous phase and gas flow rate on partitioning were studied. The partition coefficients were found to be constant in the studied range of concentration and gaseous mixture flow rate. A piece of a capillary column coated with polydimethylosiloxane can be used as a tubular denuder.
    Additional Material: 2 Ill.
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  • 22
    ISSN: 0935-6304
    Keywords: Retention factors ; styrene divinylbenzene polymer ; porous graphitic carbon ; solid-phase extraction ; water analysis ; polar organic compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---LC retention data have been measured using various stationary phases with an emphasis on highly polar to moderately polar neutral organic compounds having octanol-water partition coefficients (Kow) in log units between 0 and 3. The relationships between the retention factor measured in water and the octanol-water partition coefficient are linear but with different slopes for octadecyl (C18) silicas, and two polystyrene divinylbenzene (PS-DVB) phases with low and high surface areas. These relationships confirm that highly cross-linked polymers can provide more than 1000-times higher retention values than C18 silicas for moderately polar analytes but close values for highly polar ones. They also explain why C18 silicas and polymers are equivalent for the separation of very polar analytes. In contrast, due to a different retention mechanism, no relation exists between the retention shown by porous graphitic carbons (PGC) and analyte hydrophobicity, but highly polar analytes are in general much more strongly retained than by any other sorbent. The potential of PGC for both the extraction and the separation of analytes is shown. Due to the difference in separation mechanism, PGC is the analytical phase that should be used for confirmation of the identity of analytes instead of a cyanopropylsilica column as recommended in some environmental procedures. Applications are presented for the trace-determination of triazines and polar degradation products in ground and surface water with detection limits below the 0.1 μg/L level.
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  • 23
    ISSN: 0935-6304
    Keywords: Headspace sampling ; Headspace Sorptive Extraction (HSSE) ; SPME ; aromatic plants ; medicinal plants ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new sampling technique, Headspace Sorptive Extraction (HSSE), is here applied for the first time to the headspace sampling of medicinal and aromatic plants. The analyte partition coefficient between HSSE-PDMS stir bar and sample headspace (K1), the concentration factor (CF), the reproducibility, and the minimum recoverable amount were determined by analyzing standard solution of high volatility C5-C7 compounds with different polarities and structures (cyclohexane, propyl acetate, hexanal, 1-hexen-3-ol, isoamyl acetate, and 2-heptanol). Four aromatic and medicinal plants, viz. rosemary (Rosmarinus officinalis L.), sage (Salvia officinalis L.), thyme (Thymus vulgaris L.), and valerian (Valeriana officinalis L.) were analyzed by HSSE-GC with PDMS stir bars, and their concentration capacity was compared with those of S-HS and HS-SPME with different fibers. HSSE showed very high concentration capability with both standard and real sample components.
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  • 24
    ISSN: 0935-6304
    Keywords: Liquid chromatography ; zinc dithiocarbamate ; vulcanization accelerator ; rubber gloves ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract
    Additional Material: 2 Ill.
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  • 25
    ISSN: 0935-6304
    Keywords: Retention factors ; Cinnamomi ramulus ; high-performance liquid chromatography ; capillary electrophoresis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---No abstract
    Additional Material: 3 Ill.
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  • 26
    ISSN: 0935-6304
    Keywords: Enantioselective gas chromatography ; cyclodextrins ; heptakis(2,6-di-O-tert-butyldimethylsilyl)-β-cyclodextrin ; heptakis(2,6-di-O-tert-butyldimethylsilyl-3-O-methyl)-β-cyclodextrin ; heptakis(3,6-di-O-tert-butyldimethylsilyl-2-O-methyl)-β-cyclodextrin ; octakis(2,6-di-O-tert-butyldimethylsilyl-3-O-methyl)-γ-cyclodextrin ; thermodynamic parameters ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Separation factors and thermodynamic data for the separation of various chiral analytes on different di-O-tert-butyldimethyl-silylated cyclodextrin derivatives are collected and described. Modifying the substitution pattern of the tert-butyldimethylsilyl group in position 2 and 3 or changing from β- to γ-cyclodextrin significantly affects the separation properties of the cyclodextrin derivatives.
    Additional Material: 9 Ill.
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  • 27
    ISSN: 0935-6304
    Keywords: Capillary GC ; static and dynamic headspace sampling ; sorptive and adsorptive extraction ; plant volatiles ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Static and dynamic headspace sampling have been applied for the enrichment of volatiles emitted by living plants. For solid phase microextraction (SPME) the sorptive fibers polydimethylsiloxane (PDMS) and polyacrylate (PA) have been compared and, in accordance with the like-like principle, polar compounds exhibit more affinity for the PA fiber while apolar solutes favor the PDMS fiber. For dynamic sampling, tubes packed with PDMS particles show greater inertness than Tenax; some Tenax decomposition products, e.g. benzaldehyde and acetophenone, interfere with the analyses. With PDMS particles operated in the breakthrough mode, the obtained profiles are similar to those obtained by SPME on the PA fiber. Recoveries relative to a packed PDMS bed are 85% for Tenax, 2.4% for SPME-PDMS, and 6.2% for SPME-PA.
    Additional Material: 5 Ill.
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  • 28
    ISSN: 0935-6304
    Keywords: Comprehensive gas chromatography ; multidimensional gas chromatography ; essential oils ; coupled column analysis ; high resolution analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The essential oils from French lavender (Lavandula angustifolia) and tea tree (Melaleuca alternifolia) were separated by the two-dimensional GC technique of comprehensive gas chromatography. A coupled column combination of non-polar (5% phenyl equivalent) and polyethylene glycol phase columns was used to provide the desired resolution performance. By using a range of known standards, some of the peaks in lavender oil can be assigned. Some of these also occur in tea tree oil; however, from our knowledge of the major constituents in this oil and their relative retention behaviour, most of the major peaks may be tentatively assigned within the 2-dimensional separation space. There appear to be elution patterns within the 2-D space which should be useful in correlating retention with chemical and structural properties of the components, although this will require further evaluation. A range of coeluting peaks, which may not be so readily separated by using a single column capillary GC analysis, are resolved in the experiment described.
    Additional Material: 10 Ill.
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  • 29
    ISSN: 0935-6304
    Keywords: Monofunctionalized cyclodextrins ; enantioselective capillary-HPLC ; immobilized chiral stationary phases ; separation of chiral drugs ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Heptakis(2,6-di-O-methyl-3-O-pentyl)-β-cyclodextrin was monofunctionalized by the regioselective introduction of exactly one ω-epoxyoctyl group at the primary site of the cyclodextrin. The site-specifically substituted cyclodextrin was immobilized to commercially available aminopropyl silica by nucleophilic opening of the epoxy function of the spacer substituent resulting in a lipophilic chiral stationary phase with broad applicability for enantiomer separations in capillary-HPLC under reversed-phase conditions.
    Additional Material: 6 Ill.
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  • 30
    ISSN: 0935-6304
    Keywords: HPLC separation ; lucidin ; Rubia tinctorum ; anthraquinones ; isocratic elution ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---An HPLC method has been developed for the separation of anthraquinones with particular attention to the determination of lucidin in commercially available sources of Rubia tinctorum aglycones. Variations of chromatographic conditions have been studied in order to provide suitable resolution of anthraquinones under isocratic conditions on an end-capped RP C18-column.
    Additional Material: 2 Ill.
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  • 31
    ISSN: 0935-6304
    Keywords: Ion chromatography ; graphitic carbon stationary phases ; anions ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Inorganic anions could be separated on porous graphitic carbon stationary phases in ion chromatography. Ion exchange between eluent anions and sample anions on the stationary phase was confirmed by the retention behavior and the possibility of indirect photometric detection. The elution order of anions was different from that observed for commercially available anion exchangers. Chloride, nitrate, and sulfate contained in tap water could be determined in 7 min.
    Additional Material: 6 Ill.
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  • 32
    ISSN: 0935-6304
    Keywords: Gas chromatography-mass spectrometry ; amino acid enantiomers ; D-amino acids ; physiological fluids ; mammals ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Quantities of D-amino acids were determined in body fluids (urine, blood plasma and blood serum, milk) of mammals (hamster, horse, bovine, sheep, pig, and dog). Amino acids were isolated using a cation exchanger and converted into their N(O)-pentafluoropropionyl (or trifluoroacetyl) amino acid 2-propyl esters. Enantiomers were separated and quantified on a Chirasil-L-Val capillary column with mass spectrometric detection using selected ion monitoring. D-Enantiomers of most protein L-amino acids were detected. Largest absolute and relative amounts in most cases were determined for D-Ser and D-Ala in urine. Stereoisomers of 2,6-diaminopimelic acid were also measured in bovine, ovine, and porcine urine. Since D-amino acids were detected in all representative classes of the major orders of Mammalia, namely Artiodactyla, Perissodactyla, Rodentia, and Carnivora, and taking reports in the literature into account, it is postulated that D-amino acids occur in all mammals.
    Additional Material: 5 Ill.
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  • 33
    ISSN: 0935-6304
    Keywords: GC-MS/MS ; PCDDs ; PCDFs ; human tissue ; fish tissue ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---This paper outlines the possibilities of selectivity and sensitivity enhancement in measuring PCDD/F congeners using an ion trap GC-MS/MS. The pressure of the collision gas and the collision energy were optimized. The modified GC-MS/MS method was applied to the determination of PCDDs and PCDFs in human and fish tissues. Limits of quantification were about 1 pg/g of fat for all seventeen 2378 PCDD/Fs tested (starting amount of fat, 2 g).
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  • 34
    ISSN: 0935-6304
    Keywords: Solvation parameter model ; ystem constants for poly(dimethyldiphenylsiloxane) HP-5 and poly(ethylene glycol) HP-INNOWax stationary phases ; temperature ; molecular interaction ; retention models ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---No abstract
    Additional Material: 1 Ill.
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  • 35
    ISSN: 0935-6304
    Keywords: On-line coupling HPLC/NMR ; HPLC/ESI-MS ; (2E,4Z)-decadienoic acid ; Agromyces spec ; isolation ; structure elucidation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---No abstract
    Additional Material: 4 Ill.
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  • 36
    ISSN: 0935-6304
    Keywords: Microfabrication ; monolith ; electrochromatography ; peptides ; reactive ion etching ; reversed phase ; nanocolumns ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Monolith columns are generally fabricated by polymerization of monomers within a column. This paper reviews an alternative strategy in which the bed is microfabricated in an inorganic material by ablation. Channels of 1.5 μm width and 10 μm depth were sculpted in quartz by deep reaction ion etching. Using this approach chromatographic beds were constructed in which cubic support structures were created and arranged in rows to mimic particles in a conventional column. Beds ranging from hundreds of thousands to millions of “particles” with volumes of 15 nL to 15 μL were produced. Columns that had been derivatized with an octadecyl silane stationary phase were used to separate both low molecular weight analytes and peptides in the CEC mode. Plate height in the CEC mode was 1.2 μm at maximum efficiency.
    Additional Material: 9 Ill.
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  • 37
    ISSN: 0935-6304
    Keywords: Monolith ; continuous bed column ; convective interaction media ; membrane chromatography ; membrane adsorber ; HPMDC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Monolithic stationary phases have revolutionized protein chromatography because they combine speed, capacity, and resolution in a unique manner. Since such stationary phases contain no particles but only flow-through pores, the usual mass transfer restrictions to the chromatography of large molecules are not observed and extremely fast separations become possible. Recently the area of application of monolith chromatography has been extended to the separation and analysis of small molecules and plasmid DNA. This review summarizes the state of art in high performance monolith and especially high performance monolithic disk chromatography (HPMDC). The current understanding of the theory of protein HPMDC is summarized, while an introduction to the evolving field of small molecule HPMDC is attempted. The basic differences between the monolithic disks and columns packed with conventional stationary phases (including perfusion and micropellicular particles) but also monolithic columns (porous rods) are outlined. Finally, the potential of HPMDC to analytical and preparative biochromatography is demonstrated by a discussion of recent applications of chromatographic disks for protein isolation and bioprocess analysis.
    Additional Material: 14 Ill.
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  • 38
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0935-6304
    Keywords: In situ molecular imprinting ; continuous polymer rod ; miniaturized column ; chiral recognition ; diastereoselectivity ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Molecularly imprinted continuous polymer rods are prepared inside PEEK tubes of 1 mm i. d. by an in situ preparation technique; and chiral separations on such media have been demonstrated. The miniaturized column filled with (-)-cinchonidine-imprinted or (+)-cinchonine-imprinted polymer rods based on a copolymer of 2-(trifluoromethyl)acrylic acid and ethylene glycol dimethacrylate permitted diastereoseparation of (-)-cinchonidine and (+)-cinchonine; the template molecule is retained to a greater extent than the corresponding antipode. Increasing the amount of cyclohexanol in the polymerization mixture decreased the backpressure of the resultant rod and the addition of latex beads suspended in water to the prepolymerization mixture affected the selectivity and affinity of the imprinted polymer rods. The column length is adjusted easily by cutting, thus allowing easy control of retention behavior and analysis time.
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  • 39
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Solid-phase extraction, on-line derivatization, and measurement by ion trap mass spectrometry (ITD-MS) were used to investigate the biological degradation of pharmaceutical residues (clofibric acid, ibuprofen, diclofenac). The results of the single steps of sample pretreatment and analytical determination are reported. MS/MS measurements were performed on an ITD-MS by selecting collision induced dissociation of the molecular ions (M+) as parent ions to defined daughter ions. A pilot sewage plant and biofilm reactors operating under oxic and anoxic conditions were run as model systems with synthetic sewage water containing 10 to 50 mg/L dissolved organic carbon (DOC) and pharmaceuticals in concentrations of 10 μg/L. Clofibric acid displayed its persistent character in all cases. The pilot sewage plant and the oxic biofilm reactor showed comparable results for diclofenac and ibuprofen, which both were partly degraded. These results can explain the occurrence of these substances in sewage effluents and in the aquatic environment. A high degree of degradation was found especially for ibuprofen in the oxic biofilm reactor, which was attributed to adaptation of the biofilm to the residue. Two metabolites of ibuprofen could be identified on the basis of their mass spectra and comparison with literature data, viz. hydroxyibuprofen and carboxyibuprofen.
    Additional Material: 8 Ill.
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  • 40
    ISSN: 0935-6304
    Keywords: Programmable temperature vaporizing injection (PTV) ; thermal desorption ; gas chromatography ; mass spectrometry ; plasticizers ; polyethylene ; food wrapping film ; explosive powders ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Programmable Temperature Vaporizing Injection (PTV) has been used extensively as a means of injecting large volumes of samples to enhance sensitivity. This paper describes the use of PTV injection in the desorption mode for the analysis of a range of solid samples, and four examples of this application are described in detail. Detection by mass spectrometry was used extensively as a means of identification of the components in the various samples which were characterized.
    Additional Material: 12 Ill.
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  • 41
    ISSN: 0935-6304
    Keywords: Enantiomeric separation ; capillary electrochromatography ; positively charged polyacrylamide gel ; allyl carbamoylated β-cyclodextrin derivatives ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The novel enantiomeric separation of acidic and neutral compounds by capillary electrochromatography with β-cyclodextrin-bonded positively charged polyacrylamide gels was examined. The columns used are capillaries filled with a positively charged polyacrylamide gel, a so-called monolithic stationary phase, to which allyl carbamoylated β-CD derivatives covalently bind. The capillary wall was activated first by bifunctional reagent to make the resulting gel bind covalently inside the fused-silica tubing. Enantiomeric separations of sixteen acidic and two neutral compounds were achieved using the above-mentioned columns and 200 mmol dm-3 Tris-300 mmol dm-3 boric acid buffer (pH 8.1) as a mobile phase. High efficiencies of up to 150 000 plates m-1 were obtained for dansyl-DL-amino acids. The within-run and between-run reproducibilities of retention time and separation factor were examined for three dansyl-DL-amino acids and warfarin. The relative standard deviations of the within-run and between-run reproducibilities of retention time were less than 1.2 and 1.3% over the six injections, respectively. Those of the separation factor were less than 0.3 and 0.2%, respectively. The gel-filled capillaries were stable for at least four months with intermittent use.
    Additional Material: 6 Ill.
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  • 42
    ISSN: 0935-6304
    Keywords: Capillary electrochromatography ; monolithic column ; electroosmotic flow ; retention mechanism ; aromatic compound ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new kind of monolithic capillary electrochromatography column with poly(styrene-co-divinylbenzene-co-methacrylic acid) as the stationary phase has been developed. The stationary phase was found to be porous by scanning electron microscopy and the composition of the continuous bed was proved by IR spectroscopy to be the ternary polymer of styrene, divinylbenzene, and methacrylic acid. The effects of operating parameters, such as voltage, electrolyte, and organic modifier concentration in the mobile phase on electroosmotic flow were studied systematically. The retention mechanism of neutral solutes on such a column proved to be similar to that of reversed-phase high performance liquid chromatography. In addition, fast analyses of phenols, chlorobenzenes, anilines, isomeric compounds of phenylenediamine and alkylbenzenes within 4.5 min were achieved.
    Additional Material: 9 Ill.
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  • 43
    ISSN: 0935-6304
    Keywords: Continuous-bed ; sol-gel ; octadecylsilica ; mixed-mode stationary phase ; large-pore ; column technology ; capillary electrochromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Sol-gel bonded packing materials in continuous-bed columns have been prepared for capillary electrochromatography (CEC). Three packing materials were investigated: small-pore Spherisorb ODS1 (3 μm, 80 Å) with octadecyl as stationary phase, small-pore mixed-mode Spherisorb ODS/SCX (3 μm, 80 Å) with octadecyl and propyl sulfonic acid as stationary phases, and large-pore Nucleosil ODS (7 μm, 1 400 Å) with octadecyl as stationary phase. The characteristics of these columns were compared in terms of electroosmotic flow, efficiency, inertness, and retention factors. In contrast to columns containing sol-gel bonded ODS, columns containing sol-gel bonded mixed-mode ODS/SCX generated nearly pH independent electroosmotic flow (EOF) over pH 2-9. Columns containing sol-gel bonded large-pore ODS produced nearly three times lower reduced plate height than those containing small-pore ODS. Efficiencies of 220,000 plates per meter and 175,000 plates per meter were obtained from columns containing sol-gel bonded 7 μm, 1 400 Å ODS and columns containing sol-gel bonded 3 μm, 80 Å ODS, respectively, which are among the highest reported efficiencies for continuous-bed columns. In CEC, over one million plates per meter and pH independent EOF are expected from continuous-bed columns containing sol-gel bonded 1.5 μm particles with large pores and mixed-mode stationary phases.
    Additional Material: 11 Ill.
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  • 44
    ISSN: 0935-6304
    Keywords: Monolithic chromatography columns ; capillary electrochromatography (CEC) ; micro high performance liquid chromatography ; sol-gel based columns for chromatography ; fritless capillary chromatography columns ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Particle-loaded (3 μm, octadecylsilica) monolithic sol-gel columns have been prepared and selected characteristics measured. Several electrical properties may be calculated from simple current measurements in the column as a whole. Resistivity in the packed segment is approximately three times that in open segments, resulting in a 60% increase in field strength in the packed regions compared to the capillary with no packing. The surprisingly high specific permeability of these sol-gel columns is characteristic of 8-μm particles, which allows their operation in the microLC mode at pressures as low as 69 kPa where their efficiency is about 50,000 plates per meter and in the CEC mode where efficiency is about 106,000 plates per meter at 5 kV. There is a relatively rapid loss of efficiency with increasing linear velocity beyond 0.2 mm/s in microLC mode, which may be due to additional diffusion processes in the inter-particulate voids. A rapid loss of efficiency above 0.5 mm/s is also observed in the CEC mode, for the same reasons. Chromatographic retention behavior in either separation mode is characteristic of conventional octadecylsilica particles, indicating that analytes have significant access to the surface within the pores of the immobilized bonded phase.
    Additional Material: 6 Ill.
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  • 45
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0935-6304
    Keywords: Capillary electrochromatography ; packed columns ; fritless columns ; stationary phases ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Fritless packed silica gel columns were prepared using sol-gel technology. A part of a 75 μm i.d. fused silica capillary was filled with a mixture of tetramethoxysilane and poly(ethylene glycol). After gelling at 40°C and heating at 300°C, the resultant silica gel was derivatized with dimethyloctadecylchlorosilane. A scanning electron micrograph of a cross-section of the capillary column showed that the gel took the form of a spherical particle aggregate and adhered to the column inner wall. The column performance was evaluated for electrochromatography using acetonitrile-50 mM HEPES buffer (pH 6.6) (60/40 or 40/60, v/v) as the mobile phase. An electroosmotic flow of 1.0 mm/s was generated with (60/40, v/v) acetonitrile/HEPES buffer at a field strength of 546 V/cm. Using a sol-gel-derived packed column at an electroosmotic flow of 0.5 mm/s, efficiencies of up to 1.1×105 plates/m were obtained for retained solutes.
    Additional Material: 4 Ill.
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  • 46
    ISSN: 0935-6304
    Keywords: HPLC ; monolithic column ; silica rod column ; fast separations ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The application of a new silica-based, monolithic-type HPLC-column for fast separations is presented. The column is prepared according to a new sol-gel process, which is based on the hydrolysis and polycondensation of alkoxysilanes in the presence of water soluble polymers. The method leads to “rods” made of a single piece of porous silica with a defined pore structure, i. e. macro- and mesopores. The main feature of silica rod columns is a higher total porosity, about 15% higher than of conventional particulate HPLC columns. The resulting column pressure drop is therefore much lower, allowing operation at higher flow rates including flow gradients. Consequently, HPLC analysis can be performed much faster, as it is demonstrated by various applications.
    Additional Material: 9 Ill.
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  • 47
    ISSN: 0935-6304
    Keywords: Preparative chromatography ; silica monoliths ; PrepROD™ ; productivity ; SMB-chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The use of monolithic silica sorbents for the isolation of substances by preparative liquid chromatography is demonstrated. Preparative liquid chromatography is recognized as a valuable technique for the isolation and purification of substances in the pharmaceutical and fine chemicals industry. The system technology has meanwhile reached a high standard, and the greatest future improvements are expected to arise from new and improved adsorbents. Monolithic silica sorbents offer some unique features for preparative liquid chromatography. They exhibit high efficiencies even at high flow rates due to their fast convective mass transfer and can therefore be used at very high mobile phase velocities, leading to high productivity and hence to maximum process economy. The benefits of this new type of adsorbent are illustrated for an example in batch-chromatographic mode and an example using the continuous simulated moving bed (SMB) technology.
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  • 48
    ISSN: 0935-6304
    Keywords: Capillary electrochromatography ; monolithic columns ; synthetic polymers ; stationary phase ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Monolithic materials have quickly become a well-established stationary phase format in the field of capillary electrochromatography (CEC). Both the simplicity of their in situ preparation method and the large variety of readily available chemistries make the monolithic separation media an attractive alternative to capillary columns packed with particulate materials. This review summarizes the contributions of numerous groups working in this rapidly growing area, with a focus on monolithic capillary columns prepared from synthetic polymers. Various approaches employed for the preparation of the monoliths are detailed, and where available, the material properties of the resulting monolithic capillary columns are shown. Their chromatographic performance is demonstrated by numerous separations of different analyte mixtures in variety of modes. Although detailed studies of the effect of polymer properties on the analytical performance of monolithic capillaries remain scarce at this early stage of their development, this review also discusses some important relationships such as the effect of pore size on the separation performance in more detail.
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  • 49
    ISSN: 0935-6304
    Keywords: Sample preparation ; gas extraction techniques ; membrane-type techniques ; water analysis ; soil analysis ; gas chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---This review focuses on the role of so-called solventless methods of sample preparation in contemporary environmental analysis. The basic classification of this group of methods as well as the principal features and advantages of the techniques in current use are discussed.
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  • 50
    ISSN: 0935-6304
    Keywords: Proteomics ; protein analysis ; multidimensional HPLC ; ion-exchange chromatography ; reversed phase chromatography ; comprehensive HPLC ; two-dimensional HPLC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The interactive modes of High Performance Liquid Chromatography (HPLC) of proteins provide a platform for the construction of a multidimensional HPLC system coupled to mass spectrometry. We present a system composed of both anion and cation exchanger columns, in the first dimension, and n-octadecyl bonded 1.5 μm nonporous silica columns in the second dimension. Both columns are operated under gradient conditions. A system suitability test with standard proteins showed that the total analysis can be performed within about 20 minutes. The fractions taken from the ion exchanger column are directly analyzed within one minute on the reversed phase column at a high flow rate. Two reversed phase columns are applied and operated alternatively: while the first column performs the separation within one minute, the analytes leaving the first dimension are enriched in an on-column focusing mode on top of the second column. The sample clean-up and enrichment is performed on a novel type of restricted access cation exchanger column with internal sulfonic acid groups and external diol groups. The columns exhibit a molecular weight exclusion limit for globular proteins of about 15 kDa. Our next studies will be directed towards the analysis of proteins and peptides from extracts of fibroblasts.
    Additional Material: 4 Ill.
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  • 51
    ISSN: 0935-6304
    Keywords: Enantioselectivity ; gas chromatography ; ethylated γ-cyclodextrin ; toxaphene ; enantiomers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The enantioselectivity of three batches of octakis-(2,3,6-tri-O-ethyl)-γ-cyclodextrin (TEG-CD), which differed significantly in their degree of ethylation, is reported for toxaphene congeners. The cyclodextrin composition was determined by high performance liquid chromatography-mass spectrometry. Columns prepared with almost fully ethylated cyclodextrin showed no enantiomer separation. Increasing the average number of free OH groups up to an optimum of 3.8 allowed to resolve the following toxaphene congeners into enantiomers: Parlar no. 11, 12, 15, 21, 25, 32, 38, 42.1, 42.2, 50, 51, 56, 58, 59, 62, 69 as well as B8-1412. More free OH groups did not improve the enantiomer resolution. The structure of the polysiloxane used for dilution of TEG-CD also had an influence on the enantiomer separations achieved. Compared to OV 1701-OH, the use of PS 086 significantly improved the enantiomer resolutions of the separated congeners. However, neither increasing the column length nor the cyclodextrin amount in the stationary phase led to better separation results.
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  • 52
    ISSN: 0935-6304
    Keywords: μLC ; FID ; LC-FID ; carbohydrates ; amino acids ; alcohols ; phosphonic acids ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The potential of the on-line coupling of microcolumn liquid chromatography (μLC) using aqueous eluents with a flame ionization detector (FID) was evaluated. An eluent-jet interface was modified to allow the efficient introduction of the eluent into the FID. The potential of the method is demonstrated by the μLC-FID determination of lower alcohols and bis(2-hydroxyethylthio)alkanes on porous and non-porous stationary phases, respectively. Flow injection analysis (FIA)-FID experiments with highly polar, thermolabile, semi-volatile and non-volatile compounds like amino acids, organic acids, alkylphosphonic acids, and carbohydrates showed the developed configuration to be a promising approach for the detection of a wide range of analytes. Compared with a nebulization interface, the eluent-jet interface showed 4-10 times higher peaks for citric acid. Detection limits by FIA for all compounds were in the range of 0.2-5 ng injected. With ribose as test compound, plots of peak height vs. amount injected showed good linearity (r2 〉 0.999) in the range of 75-12,000 μg/mL. The repeatability showed relative standard deviations of less than 5%.
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  • 53
    ISSN: 0935-6304
    Keywords: Liquid chromatography ; chiral separation ; chiral stationary phase ; separation of enantiomers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new reciprocal π-basic chiral stationary phase (CSP) was designed based on the reciprocity conception of chiral recognition and prepared starting from (S)-leucine. The CSP thus prepared was applied in resolving various π-acidic N-(3,5-dinitrobenzoyl)-α-amino amides and esters and found to be very effective. Especially, N-(3,5-dinitrobenzoyl)-α-amino N,N-dialkyl amides were resolved very well on the new reciprocal CSP. From the chromatographic resolution results and based on the reciprocity conception of chiral recognition with the aid of Corey/Pauling/Koltan (CPK) molecular model studies, a chiral recognition mechanism which utilizes π-π interaction and simultaneously two hydrogen bonding interactions between the CSP and the analyte has been proposed. The CSP prepared in this study was also successful in resolving 3,5-dinitrophenylcarbamate derivatives of 2-hydroxycarboxylic acid esters.
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  • 54
    ISSN: 0935-6304
    Keywords: Conjugated linoleic acids ; underivatized ; Ag+-HPLC ; resolution ; mixed mode retention ; hydrogen bonding ; competing acid ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Fatty acids (FAs) and fatty acid residues are generally methylated and analyzed by GC. The reasons for this are partly historic and partly because of the sensitivity advantage of flame ionization detection over UV absorption by the carboxylic acid functionality in saturated FAs. However, for strongly absorbing unsaturated acids such as the conjugated linoleic acids (CLAs), the sensitivity advantage is greatly reduced. Hence there seems little reason to waste time and introduce errors associated with methylation. Remarkably, this appears not to have been recognized. In this paper we describe our method development for the analysis of underivatized CLAs by silver ion HPLC separation on the ChromSpher Lipids column. Using mobile phases previously optimized for the analysis of the methylated CLAs, retention is excessive and a competing acid is required. Various combinations of small concentrations of acetic acid (3.0-2.5%) with acetonitrile (0.0-0.025%), respectively, yield similar resolution and run times. As well as its role as a competing acid, acetic acid acts as a general strong solvent and thus can be used alone as a modifier (without acetonitrile). However, for slightly shorter run times a mobile phase of 2.5% acetic acid and 0.025% acetonitrile was chosen as the optimum mobile phase for analysis. The separation of the free CLAs is clearly superior to those previously published and obtained in this study for the methylated CLAs. The additional specific strong interactions of the underivatized CLAs seem certain to be due to hydrogen bonding between the CLA carboxylic acid functionality and the large number of residual silanols on the surface of the silica support of the stationary phase.
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  • 55
    ISSN: 0935-6304
    Keywords: Antioxidants ; propyl gallate ; octyl gallate ; dodecyl gallate ; butylated hydroxyanisole ; butylated hydroxytoluene ; reverse-phase liquid chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The influence of cationic and anionic surfactants and short-chain alcohols in the mobile phase on the retention of five antioxidants has been studied. The solutes chosen were butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and propyl, octyl, and dodecyl gallates (PG, OG, DG).The surfactants were hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), and n-propanol (PrOH) was the selected alcohol. A simple isocratic reversed-phase method for the antioxidant determination is proposed. Separation of five primary antioxidants takes 18 min with the mobile phase SDS 0.10 M/H3PO4 0.01 M/PrOH 30%. Variation of the percentage of alcohol in the mobile phase permits optimization of the retention times of the antioxidants. Detection limits in the pg range were obtained for the all solutes. The method was used to determine the antioxidants in olive oil at three different levels, giving mean recoveries close to 100% for all the solutes (BHA 102%, PG 99%, OG 99%, DG 99%) except BHT (84%).
    Additional Material: 3 Ill.
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  • 56
    ISSN: 0935-6304
    Keywords: HPLC ; industrial wastewater ; process development ; 4-amino-azobenzene-4′,5-disulfonic acid (AABDS) ; 4-amino-azobenzene (AAB) ; 4-amino-azobenzene-4′-sulfonic acid (AABS) ; 4-amino-azobenzene-4′,3,5-trisulfonic acid (AABTS) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A simple and rapid reversed-phase high-performance liquid chromatographic method for the separation and determination of 4-amino-azobenzene-4′,5-disulfonic acid (AABDS) and its process-related impurities was developed. The separation was achieved on a μ-Bondapak C18 column using 0.15 M ammonium sulfate-acetonitrile (55:45) (v/v) as eluent. A UV-visible spectrophotometric detector fixed at 386 nm was used both for detection and quantitation. The method was used not only for quality assurance but also for process development and wastewater management of AABDS.
    Additional Material: 4 Ill.
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  • 57
    ISSN: 0935-6304
    Keywords: Polyunsaturated fatty acids (PUFA) ; high performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (LC-MS with APCI) ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Analysis of polyunsaturated fatty acids using high performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry is described. The standard fatty acid methyl esters from 16 to 22 carbons were analyzed by LC-MS with APCI. The effect of orifice voltage and total carbon atoms versus number of double bonds in each homologue on the mass spectra is discussed. The correction coefficients for homologues from saturated fatty acids to hexaenoic acid are also mentioned.
    Additional Material: 4 Ill.
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  • 58
    ISSN: 0935-6304
    Keywords: Silica ; monolithic column ; aging ; mesopores ; pore size distribution ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Mesopore formation in silica gels having continuous macropores has been investigated. The macroporous wet silica gel prepared by the sol-gel process including phase separation was aged in a basic solvent making use of hydrolysis of urea in a closed condition. The mesopore structure was finally obtained by subsequent evaporation drying of solvent and heat-treatment at 600°C for 2 h. The dissolution-reprecipitation kinetics at the interfaces between wet gel skeletons and an external solvent affected the size and volume of pores formed within the skeletons. Below 120°C, mesopores suitable for various chromatographic applications have been formed typically within 24 h. On the other hand, at 200°C, the pore size attained the macropore dimensions (〉50 nm), and the whole macroporous morphology was significantly modified.
    Additional Material: 7 Ill.
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  • 59
    ISSN: 0935-6304
    Keywords: Chemiluminescence ; diol compound ; oxalate ; post-column reaction ; ruthenium complex ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---In this paper we propose a new post-column detection method for polyols containing 1,2-diol, 1,3-diol, and saccharides. The polyols are oxidized in a photochemical reactor to yield oxalate with subsequent chemiluminescence detection using [Ru(III)(bpy)3]3+. A mixing solution of eluate and oxidizing reagent is delivered to a reaction coil, which is then irradiated with ultraviolet light to promote the oxidation reaction. The detection limits for 1,2-ethanediol (ethylene glycol) and 1,3-propanediol were 38 pmol and 23 pmol, respectively.
    Additional Material: 5 Ill.
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  • 60
    ISSN: 0935-6304
    Keywords: Monolithic column ; silica monolith ; HPLC ; capillary liquid chromatography ; capillary electrochromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Two types of monolithic silica columns derivatized to form an ODS phase, one prepared in a fused silica capillary (SR-FS) and the other prepared in a mold and clad with an engineering plastic (poly-ether-ether-ketone) (SR-PEEK), were evaluated. The column efficiency and pressure drop were compared with those of a column packed with 5-μm ODS-silica particles and of an ODS-silica monolith prepared in a mold and wrapped with PTFE tubing (SR-PTFE). SR-FS gave a lower pressure drop than a column packed with 5-μm particles by a factor of 20, and a plate height of 20 μm at a linear velocity below 1 mm/s. SR-PEEK showed higher flow-resistance than the other monolithic silica columns, but they still showed a minimum plate height of 8-10 μm and a lower pressure drop than popular commercial columns packed with 5-μm particles. The evaluation of SR-FS columns in a CEC mode showed much higher efficiency than in a pressure-driven mode.
    Additional Material: 6 Ill.
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  • 61
    ISSN: 0935-6304
    Keywords: Capillary electrochromatography ; nucleosides ; short-end injection ; phenyl-bonded silica ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The influence of several experimental parameters (pH, ionic strength, organic modifier content of hydro-organic buffer) upon EOF, migration time, and retention factor has been studied in CEC with a phenyl-bonded silica column on a model mixture of five nucleosides. This paper illustrates the current interest in CEC as a method of resolving complex mixtures of neutral and ionic solutes and demonstrates the potential of the short-end injection method as a means of reducing analysis time.
    Additional Material: 4 Ill.
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  • 62
    ISSN: 0935-6304
    Keywords: On-line coupled LC-GC ; nitrogen selective detection ; NPD ; carbazoles ; PANH ; personal exposure measurement ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A coupled LC-GC method for the analysis of carbazole-type PANH has been developed and evaluated. Group separation and isolation of carbazoles from interfering acridines in a complex sample matrix was accomplished by using a back-flush technique and an in situ end-capped dimethylaminopropyl silica column in the HPLC part of the system. On-line injection of the carbazole fraction into the GC column was performed with a loop-type interface utilizing concurrent solvent evaporation technique. An LOD of 1-3 pg of individual carbazole compounds was achieved by nitrogen selective detection using an NPD. The method is shown to be robust and is demonstrated by application to personal exposure measurement in an aluminum reduction plant.
    Additional Material: 4 Ill.