bluuebunny/crossref_metadata_2025 huggingface dataset:
A new gas chromatographic retention index for pesticides and related compounds
Authors: Hall G. L. , Whitehead W. E. , Mourer C. R. , Shibamoto T.
Published: May 2005

A new gas chromatographic (GC) retention index based on a homologous series of tri‐n‐alkylamines is proposed for use in the detection of pesticides and related compounds because the standard n‐paraffin hydrocarbons used for the Kovats index do not show up well on the nitrogen‐phosphorus detectors commonly used in pesticide analysis. Using fused silica bonded phase capillary columns (DB‐1 or DB‐5), the trialkylamine indices of 106 selected pesticides and related compounds were measured and their relationship to the Kovats index determined.
Simultaneous assay of serum vitamin A and vitamin E by high performance liquid chromatography using time‐switched UV and fluorimetric detectors
Authors: Russell M. J. , Thomas B. S. , Wellock E.
Published: May 2005

An HPLC method utilizing a UV and a fluorimetric detector linked in series is described. By use of a simple integrator‐controlled time‐switched relay, analysis of serum vitamin A and E is accomplished on the same chromatogram and at optimum sensitivity for each detector. A single internal standard (retinyl acetate) monitored only by the UV detector permits measurement of both vitamins over a wide linear range. Precision of the assays is satisfactory, both on a within‐day and on a day‐to‐day basis. Recoveries of both vitamins are virtually 100% whilst sensitivity is 2 μg/L (retinol) and 0.05 mg/L (α‐tocopherol).
Analysis time in conventional and continuous development thin‐layer chromatography
Authors: Johnson E. K. , Wenning M. J. , Tecklenburg R. E. , Nurok D.
Published: May 2005

Equations for predicting analysis time in thin‐layer chromatography as a function of spot separation, solvent velocity constant, ΔRf and Rf, are presented and discussed.
Kovats and lee retention indices determined by gas chromatography/mass spectrometry for organic compounds of environmental interest
Authors: Rostad C. E. , Pereira W. E.
Published: May 2005

Retention indices of standard organic compounds of environmental interest were determined by gas chromatography/mass spectrometry, using a DB‐5 fused‐silica capillary column. Retention indices are useful references for tentative compound identification by gas chromatography, or confirmation by gas chromatography/mass spectrometry. They provide elution order for isomers that might be indistinguishable based on mass spectra. Modified Kovats and Lee retention indices are given for polycyclic aromatic hydrocarbons; sulfur heterocycles; nitrogen heterocycles; aromatic amines; oxygen heterocycles; phenols; alcohols; ketones; alkanes; nitriles; and methylesters of fatty, dicarboxylic, and aromatic acids for comparison and reference. Retention index values for heterocycles by gas chromatography/mass spectrometry are comparable with gas chromatography values previously reported.
Preparation of glass capillary columns coated with immobilized OV‐240‐OH (33% cyanopropyl substituted, OH‐terminated). An approach to improve the inertness and thermal stability of cyanoalkyl polysiloxane coatings
Authors: Blum W.
Published: May 2005

Coating intensely leached glass capillaries with OV‐240‐OH, the most polar commercially available OH‐terminated polysiloxane phase at the present time, is described. Beside chemical bonding of the phase via condensation with silanol groups of the support, additional immobilization using dimethyltetramethoxysiloxane as a crosslinker is carried out. After in situ methylation of the immobilized coating, and transformation of acidic impurities of the cyanopropyl substituted phase into the respective methyl esters, increased inertness of the column was observed. Working instructions are given, and processes involved are discussed.
Loop‐type interface for concurrent solvent evaporation in coupled HPLC‐GC. Analysis of raspberry ketone in a raspberry sauce as an example
Authors: Grob K. , Stoll J.‐M.
Published: May 2005

Presently, two coupling techniques are used for directly introducing HPLC fractions into capillary GC: The retention gap technique (involving negligible or partially concurrent solvent evaporation) and fully concurrent solvent evaporation. While the former involves use of a conventional on‐column injector, it is now proposed that concurrent solvent evaporation technique be carried out using a switching valve with a built‐in sample loop. The technique is based on the concept that the carrier gas pushes the HPLC eluent into the GC capillary against its own vapor pressure, generated by a column temperature slightly exceeding the solvent boiling point at the carrier gas inlet pressure. Further improvement of the technique is achieved by flow regulation of the carrier gas (accelerated solvent evaporation) and backflushing of the sample valve (improved solvent peak shape).

Concurrent solvent evaporation using the loop‐type interface is easy to handle, allows transfer of very large volumes of HPLC eluent (exceeding 1 ml), and renders solvent evaporation very efficient, allowing discharge of the vapors of 1 ml of solvent through the column within 5–10 min.
Quantitative analysis of ethylenediamine in plasma by capillary column gas chromatography
Authors: Heusler H. , Richter E. , Epping J. , Schmidt M.
Published: May 2005

A specific and sensitive method for the determination of ethylenediamine in human plasma is described. The aqueous sample is treated with m‐toluoyl chloride, yielding the N,N′‐bis(m‐toluoyl) derivative of the diamine, which is extracted into dichloromethane and quantitated after “on column” methylation by capillary gas liquid chromatography with alkali flame ionization detection. The corresponding derivative of putrescine serves as internal standard. The assay is reproducible and calibration curves are linear over the concentration range 0.05 to 10 μg · ml−1. The lower detection limit is about 10 ng · ml−1. The structures of the compounds of interest eluting from the capillary column are examined by gas liquid chromatography/mass spectrometry. The assay has been applied to the analysis of ethylenediamine in plasma following the administration of aminophylline and ethylenediamine in a cross‐over study to patients with bronchopulmonary diseases. The method also proves suitable for measuring other primary and secondary amines and diamines in aqueous solutions by gas liquid chromatography.
Simultaneous determination of glyceryl trinitrate and its metabolites in plasma using capillary gas chromatography with on‐column injection
Authors: Langseth‐Manrique K. , Bredesen J. E. , Greibrokk T.
Published: May 2005

A specific, sensitive, and precise assay for simultaneous quantitation of glyceryl trinitrate (GTN) and its metabolites 1,2‐and 1,3‐glyceryl dinitrate (GDN) has been developed. The method involves one single extraction step with benzene, followed by evaporation at 55°C. One μl of the extract was injected onto a capillary fused silica column with trifluoropropyl as the stationary phase. The column separated all the nitrates within 17 minutes using temperature programming from 90 to 155°C. The lower limits of detection were 0.05, 0.5, and 0.1 nmol/I for GTN, 1,2‐GDN and 1,3‐GDN respectively. The calibration curves were linear in the concentration ranges 0.05–10.0 nmol/I (GTN), 0.5–10.0 nmol/I (1,2‐GDN) and 0.1–10.0 nmol/I (1,3‐GDN). Plasma concentration data from two patients receiving intravenous GTN infusion are presented.
Limits in arson debris analysis by capillary column gas chromatography/mass spectrometry
Authors: Bertsch W. , Sellers C. S.
Published: May 2005

Sample enrichment technology and instrumental sensitivity are no longer limiting factors in arson debris analysis. When pyrolyzed, petroleum based composite materials may produce artifacts. Urban air is another major source of interference since some of the components typically found in air, in particular alkylated aromatic hydrocarbons, are customarily used as indicators for the presence of gasoline. It is suggested to replace qualitative analysis with a quantitative approach, taking the sample matrix into consideration.
The effect of column characteristics on the minimum analyte concentration and the minimum detectable amount in capillary gas chromatography
Authors: Noy Th. , Curvers J. , Cramers C. A.
Published: May 2005

The need for faster and more efficient separations of complex mixtures of organic compounds by gas chromatography has led to the development of small inner diameter open tubular columns. Owing to their decreased plate height, extremely narrow peaks are obtained. When differently sized columns with equal plate numbers are compared, injection of a fixed amount of a solute will give the highest detector signals for the smallest bore columns. When P is defined as the ratio of the column inlet and outlet pressures, it can be seen from theory that under normalized chromatographic conditions the minimum detectable amount (Qº) for a mass flow sensitive detector increases proportionally to the square of the column diameter for P = 1. In the situation of greater interest in the practice of open tubular gas chromatography where P is large, a linear relationship is derived between Qº and the column diameter.

It is a widespread misunderstanding, however, that narrow bore capillary columns should be used for this reason in trace analysis. If a fixed relative contribution of the injection band width to the overall peak variance is allowed, a decreased plate height drastically restricts the maximum sample volume to be injected. It is shown that the minimum analyte concentration in the injected sample (Cº) is inversely proportional to the column inner diameter when a mass flow sensitive detector is used. For actual concentrations less than Cº, sample preconcentration is required. The effect of peak resolution and selectivity of the stationary phase in relation to Cº and Qº will be discussed as well. The validity of the given theory is experimentally investigated. Minimum analyte concentrations and minimum detectable amounts are compared using columns with different inner diameter.
Liquid chromatographic trace enrichment with on‐line capillary gas chromatography for the determination of organic pollutants in aqueous samples
Authors: Noroozian E. , Maris F. A. , Nielen M. W. F. , Frei R. W. , de Jong G. J. , Th. Brinkman U. A.
Published: May 2005

Trace enrichment for the GC analysis of a series of chlorinated pesticides and polychlorinated biphenyls (PCBs) in aqueous samples has been achieved through a simple on‐line technique involving sorption on an LC micro‐precolumn followed by direct elution into a gas chromatograph with hexane. A 5‐m retention gap coupled to the capillary GC column served as the recipient of a relatively large sample volume (ca. 100 μl) introduced into the GC. Partially concurrent solvent evaporation during sample introduction allowed a large sample capacity. Recoveries of more than 95% were observed for the majority of the compounds studied. Using 1.0 ml aqueous samples, detection limits of less than 1 ppt were found. The applicability of the developed method was demonstrated for a river water sample.
Micro high performance liquid chromatography of aliphatic amines by means of resonance raman detection
Authors: Koizumi H. , Suzuki Y.
Published: May 2005

A micro high performance liquid chromatography coupled with a resonance Raman detection system is described. For highly sensitive Raman detection, aliphatic amines were derivatized with dabsyl chloride (4‐dimethylaminoazobenzene‐4′‐sulfonyl chloride). The derivatives were separated on an ODS micro column (0.5 mm i.d. × 145 mm PTFE tube). Chromatograms were obtained by measuring the intensity of Raman scattering at 1136 cm−1 with the 488.0 nm line of an Arion laser. The lower detection limit was 1.5 ng and the RSD of relative peak height (n = 9) was 5.9% at 11 ng of methylamine derivative. Moreover, by stopping the flow of the micro HPLC system at the retention time of the individual derivatives, it was possible to measure their resonance Raman spectra.
Evaluation of dead time calculation in liquid chromatography using a linearization procedure for homologous series
Authors: van Tulder P. J. M. , Franke J. P. , de Zeeuw R. A.
Published: May 2005

A mathematical method for the calculation of the dead time (tm) in HPLC was evaluated using a computer simulation approach, in which artificial perturbations were introduced to Simulated homolog retention times. The calculation was based on a modified and extended Grobler and Bálisz (GB) method. Investigated wav how the precision of the calculated tM is affected by: statistical fluctuations in retention times and which, and how many homolog retention times are used. Based on these simulations a two‐step procedure for the tM calculation is proposed: In the first step the linearity of log tR, n vs carbon number n is checked using as many homolog retention times as possible. The slope value bo of the first linear regression in the GB method is used for the selection of homolog retention times in the final tM calculation. In the second step the optimal selection of homologs is made and the final tM calculation is carried out. Guidelines for homolog selection are given.
Use of computerized pattern recognition in the analysis of stress induced changes in coffee aroma
Authors: Roberts D. , Bertsch W.
Published: May 2005

The aim of the study was to evaluate changes in the aroma of coffee that has been exposed to heat for some time. Coffee grinds were extracted with water. The coffee was kept hot and sampled periodically using a continuous gas phase extraction method. Gas chromatography/mass spectrometry was used to follow changes in chromatographic profiles. Data were subjected to pattern recognition. About 20 substances were found that significantly changed when exposed to heat.
Sample introduction in high speed capillary gas chromatography; input band width and detection limits
Authors: van Es A. , Janssen J. , Bally R. , Cramers C. , Rijks J.
Published: May 2005

The speed of analysis in capillary gas chromatography can be substantially increased by reduction of the column inner diameter. However, special demands are then posed upon instrumental design. In particular, the sampling system is highly critical because it has to be capable of delivering extremely small injection band widths which must be compatible with the column inside diameter. This study focuses on the evaluation of two potentially suitable sample introduction systems with respect to input band width and detection limits and their compatibility with small bore (≦ 100 μm) columns in capillary gas chromatography. One of them allows liquid on‐column injection, based on liquid splitting, of only a few nl onto small bore (≦ 100 ◂m) fused silica columns. For gases, input band widths as low as 1 ms are obtained with this system. The other one is part of a miniaturized gas chromatograph with extremely low dead volume interfaces and detector volumes. It allows input band widths for gases of a few ms. Without any preconcentration ppm concentrations are measured in gaseous samples with a 80 ◂m thick film capillary column. It will be shown that a further reduction of the minimum detectable amount and analysis time is possible with this equipment.
Concepts and comparisons in multidimensional separation
Authors: Giddings J. C.
Published: May 2005

Multidimensional separation methodology provides a mechanism for a very substantial increase in the resolving power of chromatographic and related systems. After defining the conditions required for multidimensional separation and reviewing the origin of its high resolving power, a comparison is drawn between the two principal kinds of multidimensional systems, represented by continuous two‐dimensional operation and coupled column assemblies. It is shown that their roles are complementary. The two‐dimensional system gives a broad powerful overview of a sample while the coupled column system can be used flexibly to magnify and resolve selected regions of the sample space.
Modifications of a commercial thermodesorption unit to obtain more efficient cryotrapping and compatibility with a mass selective detector (HP 5970)
Authors: Schmidbauer N. , Oehme M.
Published: May 2005

Increased O2 content of the carrier gas due to connections which were not diffusion tight and long cooling time of the cryotrap due to insufficient insulation were the main drawbacks of a commercial thermodesorption unit intended for coupling to a GC/ mass selective detector. These shortcomings were overcome by redesigning the cryotrap part and testing different seals for the desorption tube. Furthermore, the modified unit can now be easily mounted on various gas chromatographys without any risk of cold spots in the transfer line. A detailed working description of the modifications is given.
HRGC separation of hydroperoxides formed during the photosensitized oxidation of (R)—(+)‐Limonene
Authors: Schieberle P. , Maier W. , Firl J. , Grosch W.
Published: May 2005

(R)—(+)‐Limonene was photooxidized in the presence of Rose Bengal as catalyst. After TLC isolation, the hydroperoxides formed were separated directly by HRGC and analyzed by MS (El; Cl). Each hydroperoxide isomer was then isolated by HPLC for structure determination which after reduction of the HOO group with sodium borohydride was performed by 1H‐NMR and 13C‐NMR.

Six hydroperoxide isomers formed by oxidation of the endocyclic double bond were identified. The compounds eluted from the HRGC column in the following order (proportions are given in brackets) I (40.1%) (1S, 4R)‐p‐mentha‐2, 8‐diene 1‐hydroperoxide; II (5.8%) (1R, 4R)‐p‐mentha‐2, 8‐diene 1‐hydroperoxide; III (20.6%) (2R, 4R)‐p‐mentha‐[1(7), 8]‐diene 2‐hydroperoxide; IV (8.5%) (2R, 4R)‐p‐mentha‐6, 8‐diene 2‐hydroperoxide; V (4%) (2S, 4R)‐p‐mentha‐6, 8‐diene 2‐hydroperoxide; and VI (21.0%) (2S, 4R)‐p‐mentha‐[1(7), 8]‐diene 2‐hydroperoxide. Direct HRGC separation of the limonene hydroperoxides offers, inter alia, the possibility of determining their flavor qualities by HRGC/effluent sniffing.
PoraPLOT Q: A porous layer open tubular column coated with styrene‐divinylbenzene copolymer
Authors: de Zeeuw J. , de Nijs R. C. M. , Buyten J. C. , Peene J. A. , Mohnke M.
Published: May 2005

A porous polymer is deposited on the inner wall of fused silica capillary columns. The retention characteristics of this porous polymer were evaluated and found to be comparable with Porapak Q. The porous polymer has a high retention volume which enables the separation of permanent gases at ambient temperatures or higher. The hydrophobic character of the porous polymer allows the injection of water containing samples without changing retention due to adsorption of water. The inertness of the porous polymer allows the elution of a range of apolar and polar compounds. The maximum temperature of the porous polymer was estimated to be 250°C. With this new type of capillary column, high resolution separations are obtained in combination with short analysis times.
Estimation of the instrumental band broadening contribution to the column elution profiles in open tubular capillary liquid chromatography
Authors: Claessens H. A. , Hetem M. J. J. , Leclercq P. A. , Cramers C. A.
Published: May 2005

In comparison with conventionally packed HPLC columns, from a theoretical point of view, open capillary liquid chromatography (OTLC) systems offer a number of advantages like high plate numbers and short analysis times. On the other hand, drastic changes have to be made to the instrumentation. In particular, the contribution to band broadening by the chromatographic equipment must be considerably reduced. In the present study an OTLC system was developed and evaluated, which yields satisfactory results for 26 μm i. d. columns. The determination of the contribution of the chromatographic equipment to the total band broadening is discussed.
OH‐terminated cyanopropyl silicones
Authors: David F. , Sandra P. , Diricks G.
Published: May 2005

Due to their high polarity and unique selectivity, cyanopropyl silicones are basic stationary phases for high resolution capillary gas chromatography. Different OH‐terminated cyanopropyl silicones, containing a high cyanopropyl content, were synthesized and chromatographically evaluated. Special attention was paid to the degree of immobilization of the phases in FSOT columns. Depending on the problem at hand, a choice has to be made between immobilization and maximum selectivity.
Simple instrument modification for packed fused silica capillary or micro‐LC: Evaluation on the use of tubular UV‐detection cells
Authors: Vindevogel J. , Schuddinck G. , Dewaele C. , Verzele M.
Published: May 2005

Most UV detector modifications for Micro‐LC use tubular fused silica tubes (on‐column UV detection). To get a better understanding of the optical processes involved, a microcomputer model was developed in order to extract design guidelines. A gradient elution test was used for fast cell quality determination.
Gas chromatography and gas chromatography/mass spectrometry for the characterization of complex mixtures of large oligosaccharides
Authors: Karlsson H. , Hansson G. C.
Published: May 2005

High temperature gas chromatography and gas chromatography/mass spectrometry are used in the characterization of complex natural mixtures of permethylated oligosaccharides released from proteins or lipids. The high resolution allows separation of isomeric compounds and the mass range extends to oligosac‐charides around molecular mass 2000 daltons or 10 sugar residues for isomalto‐oligosaccharides. The mass spectra of permethylated oligosaccharide alditols from mucin glycopeptides are very informative and the approach allows a simple and rapid characterization of these complex components.
Sample enrichment in high speed narrow bore capillary gas chromatography
Authors: van Es A. , Janssen J. , Cramers C. , Rijks J.
Published: May 2005

Reduction of the column diameter has proved to be a highly efficient tool to increase the speed of analysis. Unfortunately, the requirements for instrumental design with respect to sample input band width, low dead volume interfacing, and time constants of detection and registration systems are the more critical the smaller the inside diameter.

Recently we reported input band widths as low as 1 ms [1] for gaseous samples at ppm concentration levels, without any preconcentration, in a study with narrow bore columns and thermal conductivity detection.

In this study a simple versatile micro on‐column cold trap/thermodesorption enrichment system for narrow bore columns is introduced and evaluated. The combination of considerable sample enrichment and preservation of the compatibility of the required input band width with column dimensions is critically examined. The process of thermodesorption (reinjection) which is the most critical step, is particularly emphasized.

The system consists of a short aluminum coated fused silica or metal capillary with a low mass and a low cost electrical heating. Input band widths down to 1 ms are obtained without extreme demands on electrical power (300 watt). The potential of the system is illustrated with some extremely fast separations.
Analysis of volatile organic chemicals in aqueous samples by purge/GC with selective water removal
Authors: Cochran J. W. , Henson J. M.
Published: May 2005

A gas chromatographic method for volatile organic chemicals in which an aqueous sample is purged directly to a cryogenically cooled, fused silica column uses a Nafion tube drier between the purge vessel and GC column. The Nafion strips water from the gas stream during the purge step while allowing volatile halocarbons and aromatics to continue to the GC column. Examples of this technique are presented on 0.53 mm and 0.25 mm fused silica columns coated with a variety of stationary phases.
Optimization of the cold split‐splitless injector in the solvent‐split mode
Authors: Termonia M. , Lacomblez B. , Munari F.
Published: May 2005

In this study, the cold split‐splitless injector recently introduced by Carlo Erba was optimized for the trace analysis of polycyclic aromatic hydrocarbons. Injections of hundreds of microliters of hexane solutions were performed in the solvent split mode using an autosampler programmed for large volume injection. Injection parameters such as type of insert, initial oven temperature, split time, and flow are shown to play important roles in defining the conditions for obtaining quantitative results. The loss of early eluting compounds can be minimized by achieving a solvent trapping effect, making use of n‐octane as co‐solvent in n‐hexane.
Quantification of mass flow effects in capillary SFC
Authors: Berger T. A.
Published: May 2005

A model for restrictor flow produces accurate predictions of flow that can be used to optimize restrictor design. The relative amplitudes of restrictor and other flows and their effect on efficiency are discussed.
Cellulose acetate as stationary phase in microcolumn LC
Authors: Kiso Y. , Takayama K. , Jinno K.
Published: May 2005

The retention characteristics of alkylbenzenes and polycyclic aromatic hydrocarbons (PAHs) have been examined in liquid chromatography on a microcapillary column packed with cellulose acetate. Particulate and fibrous cellulose acetate were used as the stationary phase. Fibrous cellulose diacetate was found to be of use as an alternative stationary phase for liquid chromatography, although the separation efficiency was low. The retention characteristics for planar PAHs were linearly correlated with the size of the molecules, but the retention behavior for alkylbenzenes and nonplanar PAHs was affected by exclusion. The retention order was strongly influenced by the addition of dimethylformamide or water to methanol in the mobile phase. The results suggested that the retention behavior is influenced by a slight change in the polymer matrix of cellulose acetate.
Applications of coupled LC‐GC: A review
Authors: Davies I. L. , Markides K. E. , Lee M. L. , Raynor M. W. , Bartle K. D.
Published: May 2005

Although coupled liquid chromatographygas chromatography (LC‐GC) was first demonstrated ten years ago, only in the last few years has there been a sudden surge of interest in the technique. Approximately 70% of the total number of LC‐GC applications have been published in the last two years (1987–88) alone. This review categorizes LC‐GC publications into four main application areas: fossil fuels, foods, environmental samples, biologiical/pharmaceutical samples, and miscellaneous samples. Multidimensional separations carried out using other coupled‐column chromatographic techniques (such as supercritical fluid chromatography (SFC) with GC, and on‐line trace enrichment‐GC) have also been included in this review.
Direct and automatic capillary GC analysis for molecular weight determination and distribution in crude oils and condensates up to C20
Authors: Durand J. P. , Fafet A. , Barreau A.
Published: May 2005

A direct and automatic method has been developed for molecular weight (MW) determination and distribution in crude oils and condensates up to C20 (340°C) by gas chromatography. Chromatographic separation has been achieved with a 50 m OV‐1 fused silica capillary column, fitted with a pre‐column to eliminate the fraction boiling above 340°C. The internal standard is added for quantification. Approximately 550 peaks have been identified by the use of GC/MS on different paraffinic, naphthenic, and aromatic crude oils or condensate samples. From identification and by correlation with MS group‐type analysis, a carbon number and a hydrocarbon group are attributed to each peak or group of peaks. Further molecular weights have been calculated from these groups. A comparison between results from this GC method and cryometry of narrow and wide fractions shows good agreement, within the precision of cryometry. An automatic identification by computer using programmed temperature indices was used for the direct determination of molecular weight. The final report gives weight percentage, molar percentage, and molecular weight for every boiling range group and hydrocarbon group.
Evaluation of a PTV injector for quantitative analysis of volatile compounds at low concentrations
Authors: Herraiz M. , Reglero G. , Herraiz T.
Published: May 2005

The performance of a PTV injector operated in the solvent venting mode with Tenax in the glass insert was evaluated with synthetic mixtures containing 5 to 50 ng of n‐alkanes, ethyl esters, n‐alcohols, and carboxylic acids.

The influence of the sampled amount, the injected volume, and the nature of the solvent on accuracy and precision were studied.

Coefficients of variation of relative (normalized) peak areas and absolute peak area ratios of each compound to the standard are of the order of 5 %.
Enantioselective capillary gas chromatography on the basis of host‐guest interactions with modified cyclodextrins
Authors: König W. A. , Krebber R. , Wenz G.
Published: May 2005

The use of per‐O‐alkylated as well as partially alkylated/acylated derivatives of α‐, β‐, and γ‐cyclodextrins as chiral stationary phases has opened many new applications to enantioselective gas chromatography. Chiral recognition is now independent of hydrogen bonding interactions and enantiomer separations are achieved for a large variety of compounds which could not be separated before, including lactones, spiroacetals, alkyl halides, olefins, and even compounds with axial asymmetry.
Rapid and quantitative extraction and analysis of trace organics using directly coupled SFE‐GC
Authors: Hawthorne S. B. , Miller D. J. , Krieger M. S.
Published: May 2005

Supercritical fluid extraction can be coupled with capillary gas chromatography (SFE‐GC) using commercially‐available on‐column or split/splitless injection ports. While liquid solvent extractions require several hours or even days to perform, SFC‐GC analyses can be completed in ≤ 1 hour including extraction, analyte concentration, and GC separation. SFE‐GC yields chromatographic peak shapes that compare favorably with those obtained using conventional liquid solvent injections. Quantitative extraction and recovery of analytes is usually achieved in 10 minutes, and maximum sensitivity is obtained since the extracted analytes can be quantitatively transferred into the GC column for cryogenic focusing prior to GC analysis. SFE‐GC analysis of a variety of organic pollutants from environmental solids and sorbent resins, and flavor and fragrance compounds from food products will be discussed.
How to avoid water contamination in the thermodesorption cryofocusing technique. Application to ethane analysis in human breath by means of an ion trap detector (ITD)
Authors: Ghoos Y. , Hiele M. , Rutgeerts P. , Vantrappen G.
Published: May 2005

The purpose of this study was to modify an automatic pre‐concentration system to avoid water contamination and to apply this technique to ethane analysis in breath. The ion trap detector was very useful in monitoring the whole analytical procedure.
Investigation of antioxidants and UV stabilizers from plastics. Part I: Comparison of HPLC and SFC; preliminary SFC/MS study
Authors: Arpino P. J. , Dilettato D. , Nguyen Khoa , Bruchet A.
Published: May 2005

Synthetic mixtures of additives (antioxidants, UV stabilizers) used in the manufacture of food packaging materials were separated by normal phase HPLC under isocratic or gradient elution, and by capillary SFC using CO2 as mobile phase. SFC proved to be more efficient for the separation and determination of additives with a wide range of boiling points and for substances lacking a UV chromophoric moiety. Combined SFC/MS, using a direct coupling interface, produced clear charge transfer spectra resembling EI spectra and proton exchange CI spectra when ammonia was added to the ion source.
Determination of free fatty acids in milk and cheese procedures for extraction, clean up, and capillary gas chromatographic analysis
Authors: De Jong Catrienus , Badings Herman T.
Published: May 2005

A rapid, reliable and precise capillary gas chromatographic method for routine quantification of short‐ and long‐chain free fatty acids (FFA) in milk and cheese is described. Procedures of (1) lipid extraction, (2) isolation of the FFA from milk and cheese extracts, and (3) capillary gas chromatographic analysis were developed and optimized. FFA can be extracted from cheese for 95–100% with ether‐heptane after grinding with sodium sulfate and addition of 2.5 M sulfuric acid. From milk, 95–100 % of the FFA (≤ C8:0) are also extracted with ether‐heptane after addition of ethanol and 2.5 M sulfuric acid. Internal standards are used to compensate for the losses of lower FFA (C2:0–C8:0) in the aqueous phase. In view of the excellent recovery (98–100 %) and a considerable saving of time, the use of an aminopropyl column is preferred for the isolation of the FFA from lipid‐extracts. The underivatized FFA are separated directly by capillary gas chromatography making use of columns which enable accurate and rapid (≤ 40 min) determination of FFA C2:0–C20:0. With the method described, all major FFA (C2:0–C18:3) in milk and cheese can be quantified with good repeatability (rsd less then 2 %). The method is also applicable to the analysis of short‐chain fatty acids in other products.
Rapid determination of volatiles in alcoholic beverages by precolumn‐backflush gas chromatography
Authors: Hagman Gunnar , Roeraade Johan
Published: May 2005

A method for quantitative determination of volatiles such as ethyl acetate, acetaldehyde, and methanol in alcoholic beverages is described. A short packed precolumn coupled to a capillary column via an effluent splitter is employed. The less volatile part of the sample is retained on the precolumn and back‐flushed using a 10‐port rotary valve, while the volatiles areseparated on the capillary column. The advantage of the system is that the analysis time per sample can be reduced to a few minutes. Moreover, the capillary column can be kept at low temperature, since it is not contaminated with material of low volatility.

The water in the sample was found to have a significant influence on the retention of the compounds (as also observed earlier by Grob und Habich [1] ). This effect was exploited to increase the resolution between ethyl acetate and methanol, by injecting a portion of pure water prior to sample injection. Apart from the better separation, the water vapor also has a deactivating effect.

The packed precolumn tolerates large amounts of non‐volatile material. Even after several hundred direct injections of wine and spirits, the chromatographic performance of the system was still satisfactory.
High‐performance liquid chromatography of proteins on short capillary columns
Authors: Mal'tsev V. G. , Nasledov D. G. , Trushin S. A. , Tennikova T. B. , Vinogradova L. V. , Volokitina I. N. , Zgonnik V. N. , Belenkii Boris G.
Published: May 2005

A microchromatographic procedure for highly sensitive analysis of proteins has been developed by using short capillary columns with reverse‐phase, ion‐exchange, and hydrophobic interaction sorbents. The high analytical mass sensitivity on the level of several nanograms was attained by the miniaturization of the column and the optimization of gradient steepness.
Comparison of the SCD and FPD for HRGC determination of atmospheric sulfur gases
Authors: Gaines K. K. , Chatham W. H. , Farwell S. O.
Published: May 2005

The FPD and the new SCD have been examined for their respective performance characteristics as sulfur selective detectors for HRGC in the determination of atmospheric sulfur gases. Overall, the SCD was an extremely selective and sensitive sulfur gas detector with lower MDLs than the FPD and fewer problems with interferences and noise stability, thus allowing the SCD more flexibility in capillary column selection. Modification of the FPD, however, provided more symmetrical peaks and greater resolution than the Sievers Model 350 SCD.
HRGC of wine free amino acids as a tool for elementary wine characterization
Authors: Vasconcelos Ana M. P. , das Neves Higuinaldo J. Chaves
Published: May 2005

In this paper we show that wine free amino acids derivatized as isopropyl N‐heptafluorobutyryl esters can be used as a tool for wine characterization. Elementary wines of eight Vitis vinifera varieties were studied during a seven year period. The characteristic wine amino acids for each variety were assessed by means of pattern recognition techniques. A “star symbol plot” was used for graphic representation.
PTV vapor overflow — principles of a solvent evaporation technique for introducing large volumes in capillary GC
Authors: Grob Konrad
Published: May 2005

The concept of a GC solvent evaporation technique is outlined that involves a modified Programmed Temperature Vaporizing (PTV) injector. The vapor overflow technique is intended for introducing samples in large volumes of solvent by syringe injection of strongly diluted samples or by coupled LC‐GC. The liquid is introduced into a packed vaporizing chamber kept above the solvent boiling point at a pressure which is near or below ambient. The carrier gas is essentially switched off. Evaporation and discharge of the solvent vapors occurs by expansion of the vapors, driven by the solvent vapor pressure. For transferring the sapmple into the column, the carrier gas is switched on again and the vaporizing chamber heated.

Compared to PTV solvent split injection, vapor overflow offers the following advantages: It automatically optimizes operational parameters, therefore facilitating its application. Losses of volatile materials are minimized by a minimal flow rate through the injector.

Vapor overflow is a promising technique for transferring watercontaining eluents in coupled LC‐GC since no wettability is required and leaching of pre‐column surfaces is avoided.
Identification of active compounds in wheat straw extracts with allelopathic activity by HRGC‐MS and HRGC‐FTIR
Authors: das Neves Higuinaldo J. Chaves , Gaspar Elvira M. Monteiro
Published: May 2005

The allelopathic effects of decomposing wheat straw have been known for some time. In spite of the ecological and economical importance of the subject, only a limited number of compounds have been asociated with the allelopathic activity of wheat straw. In this study the high resolution, speed of analysis, and sensitivity of capillary gas chromatography coupled with mass spectromtry (HRGC‐MS) and Fourier transform infrared spectrometry (HRGC‐MS‐FTIR) have been used in a systematic study of the composition of biologically active wheat straw extracts. Droplet counter‐current chromatography (DCCC) was used for fractionation and isolation of components. The extract components were analyzed as methyl derivatives and free hydroxyl groups were located by means of ethylation with diazoethane. Twenty compounds were identified, most of them being phenolic acids. Naphthoic acid, azelaic acid and 1,2,3,5‐tetrabromobenzene were also identified.
Using the tools of chromatography, mass spectrometry, and automated data processing in the detection of arson
Authors: Bertsch Wolfgang , Zhang Q. W. , Holzer Günther
Published: May 2005

The analysis of residual accelerants in fire debris is commonly carried out by a three‐step procedure: sample preparation; separation and detection; and data interpretation. Each of these steps can be optimized individually but successful analysis requires that they are compatible with each other. The isolation of residual accelerant from fire debris requires that several methods are used to cover the range of fueis that are commonly used by arsonists. Since almost all incendiary fires are set with petroleum based fuels such as gasoline or heating oil, analysis is targeted toward hydrocarbons. Capillary column gas chromatography on apolar phases is now the overwhelmingly predominant method of separation. Data interpretation is commonly carried out by visual comparison of chromatograms.

Fire debris analysis presents some unique challenges that are not often encountered in other fields. The analyte may be present at only trace levels and pyrolysis products from building materials or furnishings may dominate chromatographic patterns. Synthetic polymers may act as precursors to hydrocarbons that compete with substances typically found in petroleum based fuels. Exposure to heat and other environmental factors may also generate severe distortions in the chromatographic profiles of accelerants.

Unfortunately, there is no simple solution to these problems. Methods are available to reduce some of the chemical noise introduced by interferences and thus enhance the recognizability of the target substances. Mass spectrometry, in combination with a modern data system, is the most effective approach to filter out unwanted substances. The interpretation of the analytical results is aided by scaling, side‐by‐side comparison, or stacking of chromatograms. An additional advantage of such computerized systems is the possibility of complete automation of the analysis.

In this communication, we look at the interplay of chromatographic resolution, noise reduction by mass spectrometry, and automated data evaluation. Examples from model experiments and from simulated arson samples are presented.
Capillary electrophoresis: An integrated system with a unique split‐flow sample introduction mechanism
Authors: Tehrani Joe , Macomber R. , Day L.
Published: May 2005

The performance of an integrated capillary electrophoresis system with a novel split‐flow sample injection mechanism and special high sensitivity UV absorbance detector is described. Sample introduction into the capillary is accomplished with a standard HPLC‐type microliter syringe. The injected sample is divided proportionally between the separation capillary and an adjustable splitvent. The volume of sample introduced into the capillary can be manipulated by varying the length or the i.d. of the splitvent tubing; or the volume of sample injected. Data are presented showing reproducibility of retention time, peak height, and peak area; minimum detectability; and operation at short UV wavelengths.
Optimizing temperature program and flow rates for apillary GC analysis of EPA‐608 pesticides
Authors: Klee Matthew S. , Chang Imogene
Published: May 2005

An approach is described for optimizing chromatographic conditions for dual‐column analysis of U.S. EPA Method 608 pesticides. Sample throughput for environmental analysis of pesticides can be increased by performing the screening and confirmation analyses at the same time. This requires simultaneous injection, separation, and detection in a GC with dual inlets, columns, and detectors. Resolution maps for flow rate and temperature relationships of poorly resolved peak pairs for 5%‐phenyl methyl silicone and 7%‐cyanopropyl 7%‐phenyl methyl silicone capillary columns are presented. Resolution of target pesticides on the 5%‐phenyl methyl silicone column was much more sensitive to changes in flow and temperature‐ramp rates than was the 7%‐cyanopropyl 7%‐phenyl methyl silicone column. Optimal conditions resulted in a run time of approximately 20 min.
Optimized gas chromatographic analysis of natural pyrethrins and pyrethroids
Authors: Class Thomas J.
Published: May 2005

Gas chromatographic analysis of natural pyrethrins in insecticidal pyrethrum extract and in insecticide formulations is achieved by on‐column injection with hydrogen as carrier gas under constant flow and programmed pressure conditions. Short thin‐film fused silica capillaries (DB 5 and DB 1701) coupled to retention gaps separate the pyrethrins (cinerin I and II, jasmolin I and II, and pyrethrin I and II) and their analogue S‐bioallethrin (Esbiol) in less than twelve minutes at temperatures below 210°C without any discrimination, degradation or isomerization of thermally labile pyrethrin I and II. With S‐bioallethrin added as internal standard, spray and powder formulations are extracted with ethyl acetate and analyzed by gas chromatography with flame ionization detection for pyrethrum constituents, for other pyrethroids such as tetramethrin, cyphenothrin, cypermethrin, and for the commonly used synergist piperonl butoxide.
Capillary electrophoretic separation of amino acids: Fraction collection
Authors: Fujimoto Chuzo , Muramatsu Yoshie , Suzuki Misa , Jinno Kiyokatsu
Published: May 2005

A simple method is described which enables solutes to be collected at an electrically isolated exit after they have been separated by a free solution capillary electrophoretic system. The method is illustrated by the separation of dansyl amino acids using multiple separation capillaries.
Influence of temperature control in capillary electrophoresis
Authors: Kurosu Yasuyuki , Hibi Kiyokatsu , Sasaki Toru , Saito Muneo
Published: May 2005

We have investigated the influence of capillary temperature on migration time and peak area and have evaluated different cooling systems. It was found that for applied voltages below 15 kV (i.e. those most frequently used) temperature control effectively improves peak area reproducibility but has less effect on migration time.
The rôle of countercurrent chromatography in the fractionation of complex mixtures
Authors: Al‐Shammary Fahad Jaber , Mian Neelofur Abdul Aziz , Mian Mohammad Saleem
Published: May 2005

The biologically active pricipals in nature are frequently present as only a few parts per million of complex mixtures of non‐volatile components and often have limited stability. Their isolation often requires the application of all available techniques, such as adsorption chromatography, ion exchange procedures, size exclusion techniques, and solvent partition methods consistent with their physical properties and stability. The process of countercurret chromatography is essentially liquid‐liquid chromatography in which the stationary liquid bed is retained in the column by a force field rather than by a solid supporting matrix. Adsorption effects are thereby eliminated. The technique is particularly advantageous in the preparative separation of milligram to gram quantities of polar and labile organic compounds and bio‐particulate materials such as cells and cell fragments. Virtually any twophase solvent system, either aqueous or non‐aqueous may be employed. Countercurrent chromatography (CCC) provides a convenlent alternative to adsorption chromatography for fractionation of natural products or other complex mixtures. In some cases, this high resolution method offers advantages with regard to the avoidance of contamination from solid adsorbents, versatility, and relatively inexpensive operation. The article covers some of the applications, selection of solvents, and advantages of CCC.
Capillary supercritical fluid chromatography with flame photometric detection using a large bore column SFC pumping system
Authors: Koizumi Hitoshi , Suzuki Yoshihito
Published: May 2005

A commercially available instrument with an SFC pumping system suitable for wide bore columns (4.6 mm i.d.) has been modified for capillary supercritical fluid chromatography (CSFC) by incorporating a double‐stage flow splitter. The first flow splitter was installed in front of the sample injection valve in order to avoid a high solute split ratio. The second splitter was mounted in the column oven so that the injected sample (0.2 μL) would be split to the capillary column. In order to perform pressure programmed elution, a pressure regulating system equipped with a gradient programmer has been used. Flame photometric detection was optimized for the analysis of organosulfur compounds by CSFC. In this study, detection limits were found to be 6–14 ng and the experimentally determined exponent (n value) varied from 1.721 to 1.984 depending on the compounds tested. Sulfur‐ and phosphorus‐containing thermally labile pesticides can be chromatographed and selectively detected by using CSFC/FPD in either sulfur‐ or phosphorus mode, respectively.