bluuebunny/crossref_metadata_2025 huggingface dataset:
Injector chambers for classical GC splitless injection must be large!
Authors: Grob Konrad , Biedermann Maurus
Published: May 2005

Injector overflow is determined quantitatively by analysis of the septum purge effluent. Vaporizing chambers must have an internal volume of about 1 ml (e.g. 80 × 3.6 mm i.d.). This allows splitless injection of volumes between 1 and 2.5 μl, depending on the solvent. The septum purge should be closed during splitless transfer to prevent losses by back‐diffusion.
Analysis of pyrethrins using capillary supercritical fluid chromatography and capillary gas chromatography with fourier transform infrared detection
Authors: Wieboldt R. C. , Kempfert K. D. , Later D. W. , Campbell E. R.
Published: May 2005

The six insecticidally active components in a commercial preparation of pyrethrin extract are separated by capillary gas chromatography (GC) and by capillary supercritical fluid chromatography (SFC). Thermal degradation of pyrethrin I and II are observed under the GC conditions required to separate the pyrethrin components. The use of shorter columns and thinner stationary phase coatings reduce the amount of degradation but cannot eliminate degradation of pyrethrin II. The SFC chromatograms, obtained under thermally mild conditions, show that all components including pyrethrin II elute without degradation. Infrared spectra of cinerin I & II, jasmolin I & II, and pyrethrin I & II are obtained using a flow through SFC/IR detection cell. Spectra clearly reveal the structural differences needed to distinguish and identify the components in the extract.
Quantitation in miniaturized GC and SFC systems
Authors: Schomburg G. , Behlau H. , Häusig U. , Hoening B. , Roeder W.
Published: May 2005

Separations of high efficiency and/or speed can be achieved in capillary GC by capillary columns of lower internal diameter (< 50 μm). Sampling techniques for the analytical application of narrow bore fused silica columns have been evaluated with regard to quantitation. On‐column injection cannot be applied. Therefore liquid samples have to be vaporized in external devices before they enter the chromatographic system. Sample introduction by syringe with subsequent splitting must and can be applied but requires special syringes with perfect piston sealing because of the high inlet pressures needed even with hydrogen as carrier gas. For general analytical applications, valve systems should be developed to eliminate both the syringe and the septum from instrumental GC set‐up's.

In SFC using either narrow bore capillary or packed microbore columns, time‐controlled valve sampling with partial displacement of the sample from the loop seems to be an adequate technique because of the very high inlet pressures involved. Splitting in combination with valve operation can also be applied in capillary SFC at least to samples of good solubility in the mobile phase. A disadvantage of splitting in SFC is that another restriction for the adjustment of the split flow is necessary.
The computer‐aided optimization of capillary columns for minimum time analysis and minimum detectabiliy
Authors: Villalobos R. , Annino R.
Published: May 2005

A model utilizing the extended Golay‐Giddings equation, with an added term that expresses the instrumental contributions to the plate height, has been tested and found to accurately predict the chromatograph's output for a given set of operating conditions. The model forms the basis of a computer program that will recommend the length of column (of a specified inside diameter and film thickness) to be used (at a given temperature and input pressure) to obtain a minimum time analysis of the most difficult to separate pair of the mixture. Alternative solutions are available that specify the length of column, operating pressure, and the maximum permissible sample size required to provide a minimum analysis time for a system with specified minimum detection limits.
Quantitative determination of oxocarboxylic and hydroxycarboxylic acids in normal individuals and ketoacidotic patients
Authors: Liebich H. M. , Dotzauer A.
Published: May 2005

Oxo‐ and hydroxycarboxylic acids as metabolites of valine, leucine, and isoleucine and of ketogenesis are simultaneously quantitated in the form of their methyl esters and methyl esters/O‐methyloximes by gas chromatography using internal and external standards. Normal values for the urinary excretions of the amino acid metabolites are between 3 ± 2 μmol/24 h (mean value ± standard deviation) for 2‐oxoisocaproic acid and 122 ± 58 μmol/24 h for 3‐hydroxyisobutyric acid. In diabetic ketoacidosis the values are increased by a factor of 2‐10.
Inner wall coating of micro‐LC columns. Wall effects in LC
Authors: Verzele M. , Dewaele C. , De Weerdt M. , Abbott S.
Published: May 2005

An elastic inner wall coating in the fused silica capillaries used for Micro‐LC (LC on packed fused silica capillary columns) stabilizes the packed bed and thus increases column efficiency and life expectancy. Probably the particles of packing material are partly forced into the elastic polymer layer which thus holds the packing in position. Bonded polymers of very different chemical polarity can be used with equally good results. Variation of the coating layer thickness shows that there is an optimum value around 0.3 μm. A discussion of various wall effects in LC columns is presented. The i.d. of the columns is a most important parameter in this respect.
Analysis of the headspace of foodstuffs near room temperature
Authors: Kallio H. , Leino M. , Salorinne L.
Published: May 2005

Formation of volatiles in onion varieties, aging of coffee, and the quality of birch syrup were studied by using near room temperature headspace GC‐MS analysis. Accurate volumes (1–500 mL) of the gaseous samples were introduced into the capillary column either by a syringe or by sucking with a pump. The standard deviation of the contents was typically 1‐7% depending on the foodstuff and the compound. The ratio of 2,3‐butanedione to 2‐methylfuran decreased during the storage of coffee and was a typical measure of aging. Analysis of even the very polar 2,5‐dimethyl‐4‐hydroxy‐3(2H)‐furanone in the headspace of birch syrup was possible. The distribution patterns of the sulfur‐containing volatiles generated by crushed onions were close to each other in different varieties. The rate of the total formation of the compounds varied from cultivar to cultivar.
Systematic investigation of enantiomer resolution of N‐pivaloyl derivatized amino acid esters. Preparation of glass capillary columns coated with the chiral phase XE‐60‐L‐val‐pea
Authors: Aichholz R. , Fischer P.
Published: May 2005

A laboratory working procedure is described for silanization of glass capillaries with bis(cyanopropyl)tetramethyldisiloxane, prior to coating with XE‐60‐L‐valine‐(S)‐α‐phenylethylamide as chiral stationary phase. GC columns thus prepared exhibit good inertness and no long‐term deterioriation of enantioselectivity up to 220°C. A general procedure is given for derivatization of simple and of polyfunctional amino acids, in a batch mixture, simultaneously, and completely at both the N‐ and the C‐terminus and all other protic functions. Within the seven series of N‐pivaloyl amino acid esters tested (methyl to neopentyl), baseline separation is obtained for all R/S pairs, including the proline derivative.
Detection of C, H, N, and O in capillary gas chromatography by atomic emission
Authors: Sullivan J. J. , Quimby B. D.
Published: May 2005

Using a new atomic emission detector for gas chromatography, the quantitative and qualitative aspects of selective elemental detection of carbon, hydrogen, nitrogen, and oxygen were investigated. Sensitivity, precision, degree of tailing, and response variation between compounds are reported for capillary applications.

Earlier atomic emission detectors reported poor sensitivity and selectivity for the analysis of oxygen. These problems have been greatly reduced due to lower interactions between elements in the sample and the silica wall of the water‐cooled discharge tube.

Using near‐optimal sample amounts and chromatographic conditions, area precision was found to be very good with little variation in response factors among different compounds. For the compounds tested, response factors varied over a span of 2% to 3% for carbon, hydrogen, and nitrogen, and over 7% for oxygen. For quantitative analysis, area ratios were calibrated directly from the area ratios of two elements of an internal standard, and yielded better precision and compound independence than the individual calibrated response of each element.

Empirical formulas were calcualted using one peak as a qualitative internal standard. Unambiguous formulas were determined for some, but not all, of the compounds tested. Further increases in precision and/or compound independence is needed before empirical formula determination can be used as a routine tool.
Use of xenon as a mobile phase for on–line capillary supercritical fluid chromatography–fourier transform infrared spectrometry
Authors: Raynor M. W. , Shilstone G. F. , Bartle K. D. , Clifford A. A. , Cleary M. , Cook B. W.
Published: May 2005

Xenon is investigated as a mobile phase for on‐line capillary supercritical fluid chromatography‐Fourier transform infrared spectrometry (SFC‐FTIR). Polycyclic aromatic hydrocarbons, aromatic isocyanates, and epoxy acrylate oligomers are analyzed as examples to show that xenon has similar selectivities and solvating powe to CO2. Its optical transparency makes it ideal for IR detection. A stop flow system is constructed to increase the sensitivity of spectra measured from compounds which are weak IR absorbers.
Extending the scope of enantiomer separation on diluted methylated β‐cyclodextrin derivatives by high‐resolution gas chromatography
Authors: Nowotny H.‐P. , Schmalzing D. , Wistuba D. , Schurig V.
Published: May 2005

High‐resolution open‐tubular columns coated with solutions of heptakis(2,3,6‐tri‐O‐methyl)‐β‐cyclodextrin (Phase I) or heptakis(2,6‐di‐O‐methyl‐3‐O‐trifluoroacetyl)‐β‐cyclodextrin (Phase II) in moderately polar polysiloxanes such as OV‐1701 (5% cyanopropyl/7% phenyl/88% methylpolysiloxane) and OV‐225 (25% cyanopropyl/50% phenyl/25% methylpolysiloxane) are used for the gas chromatographic enantiomer separation of volatiles belonging to different classes of compounds. No derivatization procedures are necessary for most of the resolved chiral molecules. The chiral stationary phases can be operated between 25 and 190°C for extended periods of time. The enantiomer separation of saturated, unfunctionalized hydrocarbons clearly demonstrates the importance of molecular inclusion in chiral recognition using cyclodextrins for this class of compounds. The different, and in some cases complementary, selectivity of the Phases I and II is demonstrated.
Capillary column SFC instrumentation based on piston pumps with a programmable back‐pressure regulator for on‐line mixing of mobile phases
Authors: Anton K. , Pericles N. , Widmer H. M.
Published: May 2005

An alternative phase delivery system based on piston pumps and a back‐pressure regulator has been developed for capillary column SFC. The chromatography is not affected by the fast piston pump refill. A homogeneous on‐line mixing of binary phases with simultaneous pressure programming is easily accessible without any additional computing. Acceptable reproducibilities (< 3.5% RSD for external and < 2.0% RSD for internal standard methods) were found with mixtures of 2‐propanol/CO2 as mobile phases using UV detection and split ratios of 1:60 and 1:120. Variation and control of the split are easily done by simple flow rate volumetric changes.
An automated large volume on‐column injection technique for capillary gas chromatography
Authors: McCabe T. , Hiller J. F. , Morabito P. L.
Published: May 2005

Automated large volume (25‐200 μl) on‐column injections into a gas chromatograph with a capillary column were successfully performed by coupling a retention gap technique with an air actuated rotary valve. The linearity, injection precision, and carryover were evaluated. Slight boiling point discrimination was observed. This technique is compatible with commonly used chromatographic detectors (FID, ECD, MS) and conditions, while requiring very little instrument modification. The work is directed at the eventual reduction of manpower and turnaround time for sample collection and extraction, and Kuderna‐Danish concentration when dealing with methods similar to EPA 625.
A new method for in situ crosslinking of stationary phases on fused silica capillary columns
Authors: Liu Huwei , Zhang Aiqing , Jin Yonghao , Fu Ruonong
Published: May 2005

A new mixed crosslinking agent composed of dicumyl peroxide and tetra(methylvinyl)cyclotetrasiloxane was used to prepare fused silica capillary columns with in situ crosslinked stationary phases including PEG‐20M, SE‐54, and OV‐1. These columns proved to have good thermostability and inertness. As examples of potential applications a mixture of isomers of nitrotoluene and dinitrotoluene, and pyrolyzates of polystyrene were separated by using these columns.
HPLC determination of valproic acid in human plasma by derivatization with O‐p‐nitrobenzyl‐N,N′‐diisopropylisourea
Authors: de Illiano B. Gentile , de Gainzarain A. Quintana
Published: May 2005

A sensitive and specific method for the determination of valproic acid in plasma has been developed. After the proteins in the plasma have been precipitated with a saturated solution of ammonium sulfate in 1N HCl, the valproic acid, together with the internal standard, is extracted from the plasma with dichloromethane.

An aliquot of the organic solution is taken for derivatization of the valproic acid and the internal standard with O‐p‐nitrobenzyl‐N,N′‐diisopropylisourea.

Separation is carried out by HPLC using two chromatographic systems: an adsorption system with a μ Porasil column, hexane‐chloroform (94:6) as mobile phase, and caproic acid as internal standard and a partition reverse phase system comprising a μ Bondapak TM/C18 column, acetonitrile/methanol/0.0035 M phosphate buffer (60:10:30), and caprylic acid as internal standard. UV detection is at 254 nm.

This method, developed in both systems, permits the determination of plasma levels of valproic acid in the reported range of 50‐100 μg/mL. With adequate sensitivity, specificity, precision, and accuracy.

The plasma levels of valproic acid may be determined by this method without interference from the commonest antiepileptic drugs. Good correlation is obtained with the enzymatic immune analytic method: EMIT.
A fundamental study of the effects of modifiers in supercritical fluid chromatography
Authors: Janssen J. G. M. , Schoenmakers P. J. , Cramers C. A.
Published: May 2005

The effects of organic modifiers on retention and peak shape in packed‐column supercritical fluid chromatography were studied. The adsorption behavior of different modifiers was investigated on stationary phases consisting of hydrocarbon monolayers chemically bonded on silica. Adsorption isotherms for several modifiers were recorded using breakthrough measurements. The results were compared with those obtained by a simple method based on the injection of different sample sizes. Modifiers were selected to reflect various types of interactions with the silica support. Isotherms were found to be approximately Langmuirean. Experiments were performed to elucidate the influence of adsorbed molecules on the retention of selected test solutes.

The introduction of a solvent modifier can lead to a substantial change in the mobile phase density, the effect of which is comparable with that of an increase in the density of pure carbon dioxide. Our results confirm that the effects of low concentrations of modifiers (between 0 and 2 percent) in packed‐column SFC are largely due to deactivation of residual silanol groups on the silica support. The accessibility of the active sites was found to depend strongly on the size and structure of the modifier molecules. The decrease of retention due to the addition of low concentrations of modifiers could be described accurately by a model derived from Langmuir adsorption behavior. Some semi‐quantitative rules for the selection of modifiers and the required concentrations for optimum deactivation of the support are discussed.
Rapid and ultra‐sensitive GC/MS analyses with a microchannel plate array detector Part I: Possibilities of simultaneous ion detection in narrow‐bore GC/MS
Authors: Leclercq P. A. , Snijders H. M. J. , Cramers C. A. , Maurer K. H. , Rapp U.
Published: May 2005

Identification and detection limits for scanning and non‐scanning mass spectrometers are discussed. It is theoretically deduced and experimentally confirmed that these limits are on the low pico‐and femtogram levels, respectively, when using conventional secondary electron multiplier‐amplifier systems. The sensitivity can be increased at least tenfold by pulse‐counting techniques, instead of current amplification, provided the chemical noise is sufficiently low. The potential advantages of a detection system for simultaneous ion detection in a significant mass range, for obtaining complete mass spectra in fast GC/MS analyses, are demonstrated. A double focusing mass spectrometer was constructed, using the well‐proven Mattauch‐Herzog principles. By application of an “electronic photoplate”, substance identification in the low femtogram range on a millisecond time scale, so far only accessible for single ion monitoring techniques, is feasible.
Sampling device for a simple, fast calibration technique in gas chromatographic trace analysis of gas phases and vapor phases
Authors: Hachenberg H.
Published: May 2005

In order to accommodate continually changing tasks in the [μl/l]–[nl/m3] ranges of gas chromatographic trace analysis of gas phases and vapor phases, a simple and time‐saving calibration technique is presented which renders unnecessary conventional test mixtures of the abovementioned concentration ranges.

This new method is based on the simulation of such mixtures at the inlet of the GC unit with the aid of commercially available multiway sampling valves of various volumes by means of partial pressure sampling.
A new configuration for coupling purge‐and‐trap/cryogenic focusing/capillary column gas chromatography with splitless injection mode
Authors: Liu Shili , Kang Jiangshi , Strother Dennis L. , Carley Robert J. , Stuart James D.
Published: May 2005

A new configuration for coupling a purge‐and‐trap unit to a capillary column gas chromatograph via a cryogenic focusing interface has been developed. In this configuration, the precolumn of the cryogenic focusing interface was inserted through the septum of a split/splitless injection port where it served as both sample transfer and carrier gas supply lines. The injection port of the gas chromatograph was modified by plugging the carrier gas and the septum purge lines. This configuration allowed for the desorption of analytes at high flow rates while maintaining low, analytical‐column flow rates which are necessary for optimum capillary column operation. The capillary column flow rate is still controlled by the column backpressure regulator. Chromatograms of purgeable aromatics exhibited improved resolution, especially for early eluting components compared to those obtained by direct liquid injection using the normal splitless injection mode. Quantitative sample transfer to the analytical column afforded excellent linearity and reproducibility of compounds studied.
Automated sample clean‐up and fractionation of organochlorine pesticides and polychlorinated biphenyls in human milk using NP‐HPLC with column‐switching
Authors: Hogendoorn E. A. , van der Hoff G. R. , van Zoonen P.
Published: May 2005

A method has been developed for the automated sample pretreatment of organochlorine pesticides (OCP's) and polychlorinated biphenyls (PCB's) in extracts of human milk. This work was part of a regular monitoring program presently carried out at our institute. In this program several hundreds of human milk samples have to be analyzed for the occurrence of PCB's and OCP's.

With a normal bore straight phase HPLC system, utilizing column switching we are able to separate the fat from the compounds of interest and, moreover, complete separation of the PCB fraction from the OCP's can be achieved. Under the conditions used to separate the PCB fraction from intefering OCP's column‐switching is essential since the retention times for the OCP's vary from 4 minutes for hexachlorobenzene (HCB) to more than 2 hours for dieldrin.

1 ml of an extract containing 45 mg of fat is injected on the first (pre)column, the fat is retained on this column and the early eluting HCB, the PCB fraction, and the DDT complex are transferred to the second (analytical) column. Compounds eluting later than p,p′‐DDT are collected directly from the precolumn. Meanwhile, the PCB fraction is separated from the rest of the OCP's on the analytical column.

Contrary to conventional gravity‐controlled chromatography or solid phase extraction the clean‐up process can be monitored on‐line by UV‐detection, thus rendering a fast and reliable optimization of the system. The OCP‐fractions collected from the LC are pooled before they are transferred to a high resolution gas chromatograph equipped with a large volume option. The PCB‐fraction is injected directly in a HRGC equipped with a concurrent solvent evaporation injection device.

The limits of detection for the OCP's (HCB, α‐,β‐ and γ‐HCH, β‐Hepo (heptachlorepoxide), dieldrin, p,p′‐DDE, o,p′‐DDT p,p′‐DDT and TDE) and the PCB's investigated are at sub‐ppb level (fat basis); the recoveries vary from 80 to 100%.
Cyclodextrins as chiral stationary phases in capillary gas chromatography. Part VI: Octakis (2,3,6‐tri‐O‐pentyl)‐γ‐cyclodextrin
Authors: König W. A. , Kebber R. , Wenz G.
Published: May 2005

Perpentylated γ‐cyclodextrin is a very hydrophobic liquid which exhibits enantioselectivity toward a number of non‐polar chiral substrates including the saturated hydrocarbons cis‐ and trans‐pinane, β‐chiral olefins, iron(O) tricarbonyl complexes of prochiral olefins and 3,3,8,8‐tetramethyl‐trans‐cyclooctene, a compound with planar chirality.
Intra‐ and intermolecular interactions in the first members of homologous series of carbonyl containing compounds in gas chromatography
Authors: Golovnya R. V. , Grigoryeva D. N. , Vasilyev A. V.
Published: May 2005

Variation of the values of free energy of sorption of the methylene unit has been studied in the homologous series of n‐alkyl methyl ketones, n‐alkyl butyl ketones, n‐alkyl acetates, and methyl esters of carboxylic acids, depending on the homologue number and the temperature of analysis. The experiment was carried out on a capillary column with a thick film of immobilized Silicone SE‐54 and on packed columns with OV‐210 and Silar‐10C. An intramolecular donor‐acceptor interaction between neighboring CH3 and CO groups is assumed to be the reason for anomalously high values of free energy of sorption of the first CH2 unit in the series: RmC(O)OCH3, RmC(O)CH3, and RmC(O)C4H9. The anomaly disappeared in stationary phases containing strongly electronegative CF3 and CN groups because of specific inter molecular interactions.
Automated on‐line HPLC‐HRGC with gradient elution and multiple GC transfer applied to the characterization of citrus essential oils
Authors: Munari F. , Dugo G. , Cotroneo A.
Published: May 2005

Citrus essential oil analysis is characterized by the complexity of the separation of all the components which may belong to different classes of compounds and be present in a wide range of concentrations.

Capillary GC is the best technique for characterizing the volatile fraction of citrus essential oil. In many cases, however, this technique does not achieve complete separation of all the components.

A combination of LC and HRGC in off‐line methods is necessary to achieve complete resolution of the minor components present in the oil and in general to facilitate the identification of the components belonging to different classes. Very recently we have demonstrated the possibility of using on‐line HPLC‐HRGC coupling for fractionation and identification of alcohols in lemon oils.

In the present work, a fully automatic HPLC‐HRGC instrument was used for the pre‐separation of the essential oils into the various classes of compounds, using gradient elution and multiple fraction transfer into the capillary column.

This method allowed a pre‐separation of the components into four major classes of compounds: hydrocarbons, aldehydes, esters, and alcohols before their transfer into the GC. A good correlation with the existing off‐line methods was found.

The ability of the Instrument to perform, In a fully automatic way, HPLC pre‐separation with gradient elution and GC transfer of more than one fraction from a single HPLC injection, was found to be very useful for routine characterization of various essential oils.
Ethyl acetate for the desorption of a liquid chromatographic precolumn on‐line into a gas chromatograph
Authors: Vreuls Jolan J. , Cuppen Wilhelmus J. G. M. , De Jong Gerhardus J. , Th. Brinkman Udo A.
Published: May 2005

The feasibility of using ethyl acetate for the desorption of trace pollutants from a liquid chromatographic precolumn on‐line into a diphenyltetramethyldisilazane‐deactivated retention gap and, subsequently analysis by means of capillary gas chromatography has been demonstrated. First 5% of methanol are added to the water sample to prevent sorption of analytes onto parts of the preconcentration system. About 1 ml of this aqueous sample is injected onto a precolumn containing a polymeric stationary phase, using water–methanol (95:5, v/v) for transport and clean‐up. The precolumn is desorbed with ethyl acetate and a fraction of 75 μl is injected on‐line into the retention gap; separation is then achieved on a capillary CP Sil 19 column. No breakthrough of the test compounds was observed in the preconcentration step. The recovery was quantitative and the response obtained with flame ionization detection was linear in the range 0.1–100 ng/ml. The effect of varying the sorption flow rate on the recovery was studied. The system was applied to the analysis of river water.
Computer‐assisted optimization of selectivity (mobile phase, pH, and ion concentration) in high‐perfomance liquid chromatography
Authors: Qin‐Sin Wang , Ru‐Yu Gao , Heng‐Yan Wang
Published: May 2005

A computer‐assisted method is presented for optimization of mobile phase composition in reverse‐phase and normal‐phase HPLC. The method is based on window diagrams, but only three preliminary tests are required. The method is successfully applied to two examples and there is good agreement between predicted and experimental results. Optimal values for ion concentration and pH in ion chromatography from a published optimization method are compared to values calculated using the computer‐assisted method presented in this paper. The same results are obtained, but the method presented here is simpler and faster than previously published one.
Quantitative determination of paraffin oil in blood by capillary gas chromatography
Authors: Tsikas Dimitrios , Brunner Georig
Published: May 2005

A capillary gas chromatographic method is described for the quantitative determination of liquid paraffin in blood. Paraffin is extracted from blood into n‐heptane. After solvent evaporation and dissolution of the residue in 100–200 μl n‐heptane one μl is injected into a gas chromatograph fitted with a fused silica capillary column (Permabond® OV‐1‐CB‐0.1, 10 m × 0.32 mm i.d.) and flame ionization detector. Analysis is performed by using an oven program [50°C (3 min)−285°C (5 min), rise 10%min]. The sensitivity (1.5 ng hexadecane) and the reproducibility prove the applicability of the method for the determination of liquid paraffin in blood and for the study of the stability of the liquid paraffin hollow fiber membranes used in an extracorporeal liver support system.
Microbore columns vs. open tubular columns for supercritical fluid chromatography in environmental analysis: Separation of polychlorinated biphenyls and terphenyls
Authors: Onuska Francis I. , Terry Ken A. , Rokushika Souji , Hatano Hiroyuki
Published: May 2005

The supercritical fluid chromatographic behavior of polychlorinated biphenyls (PCBs) and polychlorinated terphenyls (PCTs) is described. The method uses a microbore C‐18 column and an open tubular capillary column coated with SE‐52 and carbon dioxide as the supercritical fluid. Factors affecting the separation and retention of these compounds are discussed.
Variable splitter for regulation of the solvent evaporation rate in the coupling of liquid chromatography with gas chromatography
Authors: Dolecka Ewa , Vreuls Jolan J. , de Jong Gerhardus J. , Th. Brinkman Udo A. , Maris Frans A.
Published: May 2005

A system is described which accelerates the solvent evaporation rate in the retention gap. The evaporation is due to a saturation effect of the carrier gas stream, and a considerable increase in evaporation rate is obtained by inserting a split outlet between the retention gap and the capillary separation column in the gas chromatograph. By varying the backpressure of the spliter device, the flow rate through the retention gap can be adjusted and so too the evaporation rate. The evaporation process was monitored by inserting a dectecter in the split outlet line. The technique was applied to the on‐line LC trace enrichment/GC analysis of water containing a mixture of polycyclic aromatic hydrocarbons.
Qualitative supercritical fluid extraction coupled to capillary gas chromatography
Authors: Levy Joseph M. , Rosselli Athos C. , Boyer David S. , Cross Kathryn
Published: May 2005

The usefulness and ease of utilizing supercritical fluid extraction (SFE) directly coupled to capillary gas chromatography (GC) as quantitative or qualitative analytical problem‐solving tools will be demonstrated. As an alternative to conventional liquid solvent extractions, SFE presents itself as a means to achieve high extraction efficiencies of different compounds in complex solid matrices in very rapid tims frames. Moreover, SFE has an additional advantage of being able to achieve distinct extraction selectivities as a function of the solubilizing power of the supercritical fluid extracting phase. For on‐line SFE/GC, the extraction effluent is directly transferred to the analytical chromatograph. On‐line SFE/GC involves the decompression of pressurized extraction effluent directly into a heated, unmodified capillary split injection port of the GC. In this respect, SFE introduction into GC can be used as an alternative means of GC injection, comparable to such modes of injection as pyrolysis and thermal desorption. This paper will show applications of SFE/GC where mass spectrometric detection together with flame ionization detection was used for component identification from environmental, tobacco, and petroleum matrices.
An investigation of gas chromatography with atomic emission detection for the determination of empirical formulas
Authors: Wylie Philip L. , Sullivan James J. , Quimby Bruce D.
Published: May 2005

The atomic emission detector (AED) is a valuable tool for the identification of unknowns in complex mixtures. To the extent that elemental response factors are independent of compound structure, gas chromatographic results allow calculation of atomic ratios for unknown compounds. In favorable cases, empirical formulas can be found. An algorithm for automated calculation of empirical formulas for all the peaks in a chromatogram has been developed. When finite accuracy prevents an exact determination of empirical formulas, the algorithm gives a list of all formulas for each compound which are compatible with the user‐defined limits.

Examples are given of calculations for fatty acid methyl esters, substituted phenols, and pesticides. Analyses of volatile pollutants and polychlorinated biphenyls reveal a nonlinearity for hydrogen response, and an interference of chlorine on hydrogen. A lubricating oil analysis is used to illustrate the identification of unknowns.
Direct injection of large sample volumes into capillary columns with packed column injector
Authors: Watanabe Chuichi , Hashimoto Keiji
Published: May 2005

A direct injection method for large volume samples which avoids severe tailing of the solvent peak has been developed using a packed column injector (up to 100 μl) leading into an ordinary capillary column (0.3 mm i.d.). Modifications are made to the cooler zones of the inlet port and on the carrier gas flow control system. This injection technique is based on the effective use of phase soaking and cold trapping using a retention gap. The large volume of solvent vapor is rapidly purged out of the injector with a higher flow of carrier gas while the solutes trapped at the head of the column are subsequently analyzed with another optimum flow rate. The proposed carrier gas flow regulation system is also compared with conventional split/splitless injection methods.
Electron capture ion mobility spectrometry for the selective detection of chlorinated and brominated species after capillary gas chromatography
Authors: St. Louis Robert H. , Hill Herbert H.
Published: May 2005

This paper reports the first investigation of electron capture ion mobility spectrometry as a detection method for capillary gas chromatography. In previous work with negative ion mobility detection after gas chromatography, the principal reactant ion species were O2− or hydrated O2− due to the presence of oxygen in the drift gas. These molecular reactant ions have a mobility similar to chloride and bromide ions, which are the principal product ions formed by most halogenated organics via dissociative ion‐molecule reactions. Oxygenated reactant ions thus interfere with the selective detection of chloride and bromide product ions. A recently described ion mobility detector design efficiently eliminated ambient impurities, including oxygen, from infiltrating the ionization region of the detector; consequently, in the negative mode of operation, the ionization species with N2 drift gas were thermalized electrons. Thermalized electrons have a high mobility and their drift time occupies a region of the ion mobility spectrum not occupied by chloride, bromide, or other product ions. The result was improved selectivity for halogenated organics which ionize by dissociative electron capture. This was demonstrated by the selective detection of 4,4′‐dibromobiphenyl from the components of a polychlorinated biphenyl mixture (Aroclor 1248).
Recent advances in supercritical fluid chromatography/mass spectrometry
Authors: Olesik Susan V.
Published: May 2005

A summary of the recent advances in SFC/MS is included in this review. Interface designs are described as well as the key control variables. Finally, future developments in SFC/MS are predicted.
Structure‐type separation of diesel fuels by solid phase extraction and identification of the two‐ and three‐ring aromatics by capillary GC‐mass spectrometry
Authors: Bundt Joachim , Herbel Walter , Steinhart Hans , Franke Stefan , Francke Wittko
Published: May 2005

A simple and effective solid phase extraction (SPE) method using silica gel micro glass columns has been developed for the separation of diesel fuel into groups of aliphatic, and mono‐, di‐ and polyaromatic hydrocarbons. It is based on a stepwise gradient of dichloromethane in n‐pentane. The resulting fractions were analyzed by capillary gas chromatography with a flame ionization detector and coupled gas chromatography‐mass spectrometry.

Commercially available standards, and retention indices and mass spectra were used for identification of individual aromatic compounds. The principal polycyclic aromatic hydrocarbons (PAHs) in diesel fuel are naphthalene, biphenyl, fluorene, phen‐anthrene and their alkylated derivatives. Sulfur‐containing PAHs are mainly represented by methyl‐substituted dibenzo‐thiophenes.
A polymeric liquid crystal capillary column for GC‐MS analysis of PCDD and PCDF
Authors: Albrecht Iris D. , Naikwadi Krishnat P. , Karasek Francis W.
Published: May 2005

A newly developed side chain liquid crystal polysiloxane has been investigated as a stationary phase for the isomer‐specific analysis of polychlorinated dibenzo‐p‐dioxins and polychlorinated dibenzofurans substituted at positions 2, 3, 7, and 8. The retention times from the chromatograms of a standard solution containing all PCDD and PCDF isomers were compared with those from solutions containing only those tetra‐ to octa‐chlorinated compounds substituted at positions 2, 3, 7, and 8. In general, PCDDs substituted at positions 2, 3, 7, and 8 eluted later than most other isomers of the same congener group. The separations obtained on this stationary phase were compared with those obtained elsewhere using a commercially available product.
On‐line coupled HPLC‐HRGC: A powerful tool for vapor phase FTIR analysis (LC‐GC‐FTIR)
Authors: Full Gerhard , Krammer Gerhard , Schreier Peter
Published: May 2005

The design of an on‐line LC‐GC‐FTIR system using an on‐column interface and partially concurrent solvent evaporation with early vapor exit is described. The integration of LC‐GC coupling into vapor phase FTIR analysis enables problems of sensitivity encountered with HRGC‐FTIR detection to be over‐come. The applicability of the method is demonstrated by the identification and determination of citropten and bergapten in bergamot oil.
GC‐MS investigation of α‐polyfluoroalkylbenzyl phosphorus esters
Authors: Shcherbina T. M. , Laretina A. P. , Goryunov E. I. , Kabachnik M. I.
Published: May 2005

The stereochemistry of some α‐polyfluoroalkylbenzyl phosphorus esters has been studied by capillary gas chromatography (CGC). The compounds are mixtures of two or three diastereomers, depending on the number of asymmetric centers and the molecular symmetry. The primary fragmentation processes in the mass spectra of the phosphorus esters and their deuterated analogous have also been studied.
Determination, by GC‐MS using deuterated internal standards, of formaldehyde and methanol evolved during curing of coatings
Authors: McGuire Jeffrey M. , Nahm Steven H.
Published: May 2005

A quick and accurate capillary GC‐MS method based on dynamic headspace analysis has been developed for elucidating the curing chemistry and evaluating the degree of curing of new high performance coatings. This method quantitatively analyzes volatile reaction products, particularly formaldehyde and methanol, evolved from these coatings during curing. The reaction volatiles are cryogenically trapped, and then chromatographed with deuterated formaldehyde and methanol as internal standards. The relative standard deviations of the method are 3–6% and 1‐2% for determinations of formaldehyde and methanol, respectively.
Microcolumn liquid chromatography of the enantiomers of organophosphorus pesticides with thermionic and ultraviolet detection
Authors: Kientz Charles E. , Langenberg Jan P. , de Jong Gerhardus J. , Th. Brinkman Udo A.
Published: May 2005

Microcolumn liquid chromatography (micro‐LC) of some chiral organophosphorus pesticides has been studied using Chiralcel OD columns and simultaneous ultraviolet (UV) and phosphorus selective detection, the latter by means of a micro‐UV cell coupled on‐line to a thermionic detector (TID). Micro‐LC showed a ca. 5‐fold improved separation impedance, a ca. 1.8‐fold increased column permeability, and greater inertness compared with conventional LC.

By using the TID, organophosphorus pesticides could be satisfactorily determined at trace levels, the detection limit being 4 pg/s of phosphorus. The response of the micro‐LC‐TID system is linear in the range of 0.05–20 ng (r = 0.9994).
Determination of the migration times of flow measurement markers in CEC
Authors: Hanai Toshihiko , Hatano Hiroyuki , Nimura Noriyuki , Kinoshita Toshio
Published: May 2005

The electroosmotic migration times of fructose, water, and phenol have been measured in several solutions. The electroosmotic flow rate was fundamentally dependent on buffer concentration and on the concentration of additives such as sodium chloride; additives such as methanol and sodium dodecylsulfate did not influence the flow rate, yet tetrabutylammonium bromide had a significant effect.
Analysis of organic solvents in printing inks by headspace gas chromatography – mass spectrometry
Authors: Rastogi Suresh Chandra
Published: May 2005

Static headspace analysis by gas chromatography has been found to be a suitable method for the analysis of organic solvents in printing inks. Experimental conditions for the analysis have been optimized, and the accuracy and relative standard deviation of the method has been determined. The solvent content of 29 printing inks has been measured.
Analysis of seven chlorobiphenyl congeners by multidimensional gas chromatography
Authors: de Boer Jacob , Dao Quy T.
Published: May 2005

Chlorobiphenyl congeners (CBs) are used as indicator compounds in analysis performed to determine whether or not PCB concentrations in food products, waste mineral oil, and environmental samples comply with the maximum levels permitted by legislation. Seven of these compounds have been checked for coelution with other CB congeners by means of a multidimensional gas chromatographic method utilizing a combination of two narrow bore columns, one coated with a conventional non‐polar stationary phase and the other with a liquid crystalline (smectic) stationary phase.

Peaks of the relevant CBs have been transferred, by heart cutting, from the non‐polar column to the liquid crystal column, on which unambiguous separation from possible coeluting CB congeners was obtained. It has been shown that if the seven congeners are analyzed solely on a single, non‐polar capillary column the results obtained for two of them may be affected by coelution of other compounds.
Analysis of pheromones: Enrichment on thick film capillary traps and GC detection with a living detector (EAD)
Authors: Burger Barend V. , Nell Anika E. , Petersen Warren G. B.
Published: May 2005

Insect pheromones and other insect semiochemicals have been concentrated in capillary traps for thermal desorption and gas chromatographic separation. Whereas highly volatile compounds are not quantitatively retained by traps short enough to enable thermal desorption in the injector, quantitative trapping is possible on longer fused silica traps. Short traps coated with a 145 μm film of a polysiloxane were used for the quantitative determination of the constituents of a dung beetle attractant. By means of a “living detector” with the antenna of an insect as sensing element the compounds eluting from a gas chromatographic column, were screened for possible semiochemical activity.
Gas chromatographic separation of protein amino acids in four minutes
Authors: Hušek Petr , Sweeley Charles C.
Published: May 2005

A method is presented for analysis of protein amino acids in five minutes, including derivatization. The chemical treatment involves reaction with ethyl chloroformate: if the composition of the reaction medium is optimum this reagent esterifies carboxylic groups simultaneously with derivatization of other reactive groups and the reaction is complete in seconds. The moderately polar silicone OV‐1701 was found to be a convenient liquid phase for separation of the derivatives: a five meter capillary column of internal diameter suitable for routine use was able to separate the amino acids in four minutes. Derivatization of arginine was incomplete and it failed to elute from the column.
Analysis of chemical warfare agents in water by solid phase extraction and two‐channel capillary gas chromatography
Authors: Häkkinen Vesa M. A.
Published: May 2005

Solid phase extraction with commercial C‐18 cartridges has been applied to the analysis of some well known chemical warfare agents in water samples. Different sample pretreatment and cartridge conditioning procedures, and different extraction solvents were tested to study the optimum conditions for efficient extraction and recovery of the compounds of interest. The eluates were analyzed with a two‐channel gas chromatograph equipped with an autosampler and a retention index monitoring system.

The suitability of this technique for real samples is discussed: the rapid hydrolysis of many of the compounds studied and the poor recoveries of the polar degradation products are practical limitations of the method.
Supercritical fluid extraction of polychlorinated dibenzo‐p‐dioxins from municipal incinerator fly ash
Authors: Onuska Francis I. , Terry K. A.
Published: May 2005

The supercritical fluid extraction of polychlorinated dibenzo‐p‐dioxins from an incinerator fly ash sample has been investigated; supercritical nitrous oxide and its mixtures with methanol and toluene were employed as mobile phases.

Recoveries of individual polychlorinated dibenzo‐p‐dioxins congeners were calculated from results of analysis of 13C‐labeled dioxins by high resolution GC‐MS employing selected ion monitoring. The extraction procedure was compared with extraction in a Soxhlet apparatus, which is currently used as a standard method for removing chlorinated dibenzo‐p‐dioxins from fly ash samples: the results indicated that the time required for the extraction and clean‐up can be reduced from 24 to 2.5 hours/sample. Quantitative recovery of the chlorinated dibenzo‐p‐dioxins was achieved at μg/kg levels, the relative standard deviation was between 1.8 and 5.8%.

The use of a virtually inert fluid such as pure nitrous oxide provides significant improvement over conventional extraction procedures because no solvent residue is left in the processed extract.
Some practical experiences in the use of a solventless injection system for packed column supercritical fluid chromatography
Authors: Oudsema John W. , Poole Colin F.
Published: May 2005

The operating characteristics of a solventless injector for packed column supercritical fluid chromatography are described. Successful operation depends on the difference between the volatilities of the analytes and the solvent or matrix being sufficient for their separation by gas purging in a thermostatted precolumn, and also on the existence of an effective re‐focusing mechanism at the head of the analytical column for the sample dissolved in liquid or supercritical fluid carbon dioxide. The latter is easily achieved in density programmed operation by stationary phase trapping at low fluid densities or phase ratio trapping by changing the temperature at low to moderate fluid densities. The solventless injector can easily accommodate sample volumes from 1–100 μl and is easily adapted for in‐line derivatization using reagents which can, after reaction, be eliminated by gas purging. For general purposes the solventless injector can be used to overcome most of the problems encountered when rotary valve loop injectors are used with small bore packed columns, and will probably replace this type of injector as the injector of choice for supercritical fluid chromatography with mobile phases of low polarity.
Studies of grass forages and their fibrous fractions by pyrolysis gas chromatography – ion trap detection
Authors: Piccaglia Roberta
Published: May 2005

Grass forage samples with different fiber content and composition, and their fibrous fractions, have been analyzed by pyrolysis – gas chromatography with ion trap detection. The identities of the pyrolysis fragments indicated their origin to be carbohydrates, lignin, and nitrogen compounds. Comparison of the resulting quantitative data by factorial variance revealed pyrogram peaks attributable to neutral detergent fiber, cellular contents, and lignin. Quantitative pyrolysis data from these components showed the same trends as those recorded by the method of Goering and Van Soest [1].
Direct supercritical fluid extraction of nitrogenous bases from aqueous solution
Authors: Hedrick Joseph L. , Taylor Larry T.
Published: May 2005

The feasibility of using supercritical carbon dioxide for both static and dynamic extraction of organic bases from an aqueous matrix has been investigated. It appears that the greater the lipophilic portion of the molecule the more readily is the base extracted: triprolidine, sulfamethazine and caffeine were extracted whereas picolinic acid, succinonitrile, and nicotine were not.