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GC System (gc + system)

Distribution by Scientific Domains

Chemistry	50%
Physics and Astronomy	37%

Selected Abstracts

Quantitation of valproic acid in pharmaceutical preparations using dispersive liquid-liquid microextraction followed by gas chromatography-flame ionization detection without prior derivatization

DRUG TESTING AND ANALYSIS, Issue 7 2010
Hamid Reza Sobhi
Abstract Dispersive liquid-liquid microextraction (DLLME), coupled with gas chromatography-flame ionization detection (GC-FID), has been successfully used for the extraction and determination of valproic acid (VPA) in pharmaceutical preparations. In the developed method, an appropriate mixture of extracting and disperser solvents was rapidly injected into an aqueous sample. Having formed a cloudy solution, the mixture was centrifuged and then the extracting solvent was sedimented at the bottom of a conical test tube. The extract was then injected into a GC system directly, without any further pretreatment. Initially, microextraction efficiency factors were optimized and the optimum experimental conditions found were as follows: tetrachloroethylene (9.0 µL) as extracting solvent; acetone (1.0 mL) as disperser solvent; 5 mL acidic aqueous sample (pH 1) without salt addition. Under the selected conditions, the calibration curve showed linearity in the range of 0.1,5.0 mg/L with regression coefficient corresponding to 0.9998. The limit of detection was found to be 0.05 mg/L. Finally, the method was applied for the determination of VPA in two different pharmaceutical preparations. A reasonable intra-assay (3.9,10.8%, n = 3) and inter-assay (5.6,11.4%, n = 3) precision illustrated the good performance of the analytical procedure. The protocol proved to be rapid and cost-effective for screening purposes. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Detectability enhancement of spectrophotometric detectors by the use of multidimensional gas chromatography

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 18 2002
Juan Carlos Medina
Abstract Multidimensional gas chromatography (2D GC) is demonstrated as a way to improve limits of detectability of spectrophotometric detectors. UV and IR detectors are generally less sensitive than mass spectrometers or other GC detectors. This has placed some limitations on the useful capabilities provided by spectrophotometric detectors, such as the ability to provide structure-related information for a particular analyte. In this paper, we report results from interfacing a 2D GC instrument to a UV detector. Symmetry factor and the ratio of retention time divided by peak width did not show deterioration of the quality of chromatography when a megabore column was used with this detector. Furthermore, an increase in the limits of detectability over that attainable in a single-column system was realized by using the 2D GC system. However, the low flow (1 mL/min) imposed by the use of a microbore column (250 ,m ID) caused significant tailing when the UV detector was used. [source]

Comprehensive two-dimensional gas chromatography-mass spectrometry: A review

MASS SPECTROMETRY REVIEWS, Issue 2 2008
Luigi Mondello
Abstract Although comprehensive two-dimensional gas chromatography (GC,×,GC) has been on the scene for more than 15 years, it is still generally considered a relatively novel technique and is yet far from being fully established. The revolutionary aspect of GC,×,GC, with respect to classical multidimensional chromatography, is that the entire sample is subjected to two distinct analytical separations. The resulting enhanced separating capacity makes this approach a prime choice when GC analysts are challenged with highly complex mixtures. The combination of a third mass spectrometric dimension to a GC,×,GC system generates the most powerful analytical tool today for volatile and semi-volatile analytes. The present review is focused on the rather brief, but not scant, history of comprehensive two-dimensional GC-MS: the first experiments were carried out at the end of the 1990s and, since then, the methodology has been increasingly studied and applied. Almost all GC,×,GC-MS applications have been carried out by using either a time-of-flight or quadrupole mass analyzer; significant experiments relative to a variety of research fields, as well as advantages and disadvantages of the MS systems employed, are discussed. The principles, practical and theoretical aspects, and the most significant developments of GC,×,GC are also described. © 2008 Wiley Periodicals, Inc., Mass Spec Rev 27:101,124, 2008 [source]

An extensive study of dynamical friction in dwarf galaxies: the role of stars, dark matter, halo profiles and MOND

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
F. J. Sánchez-Salcedo
ABSTRACT We investigate the in-spiralling time-scales of globular clusters (GCs) in dwarf spheroidal (dSph) and dwarf elliptical (dE) galaxies, due to dynamical friction (DF). We address the problem of these time-scales having been variously estimated in the literature as much shorter than a Hubble time. Using self-consistent two-component (dark matter and stars) models, we explore mechanisms which may yield extended DF time-scales in such systems in order to explain why dwarf galaxies often show GC systems. As a general rule, dark matter and stars both give a comparable contribution to the dynamical drag. By exploring various possibilities for their gravitational make-up, it is shown that these studies help to constrain the parameters of the dark matter haloes in these galaxies, as well as to test alternatives to dark matter. Under the assumption of a dark halo having a central density core with a typical King core radius somewhat larger than the observed stellar core radius, DF time-scales are naturally extended upwards of a Hubble time. Cuspy dark haloes yield time-scales ,4.5 Gyr, for any dark halo parameters in accordance with observations of stellar line-of-sight velocity dispersion in dSph galaxies. We confirm, after a detailed formulation of the DF problem under the alternative hypothesis of modified Newtonian dynamics (MOND) and in the lack of any dark matter, that due to the enhanced dynamical drag of the stars, the DF time-scales in MOND would be extremely short. Taking the well-measured structural parameters of the Fornax dSph and its GC system as a case study, we conclude that requiring DF time-scales comparable to the Hubble time strongly favours dark haloes with a central core. [source]

Group-specific component (GC) in curiaú and pacoval, two african-derived brazilian populations

AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 6 2001
Silviene Fabiana De Oliveira
The group-specific component (GC) system is of interest in anthropological genetic studies because the distribution of its subtypes distinguishes among major ethnic groups. The GC system was analyzed in Curiaú and Pacoval, two remnant Quilombo populations (African-derived populations) from the Brazilian Amazon. There was no significant statistical difference in allelic frequencies between the two populations or between them and three other African-derived Brazilian populations (Mimbó, Sítio Velho, and Gaucinha in Northeastern Brazil). These populations share similarities among themselves and with African populations (high frequencies of GC*1F and lower frequencies of GC*1S), which may reflect the influence of a high level of African contribution to their formation, but there is a clear difference between them and Europeans and South American Indians. It is suggested that the GC system is a useful marker for studying relationships between single populations and major ethnic groups, but does not discriminate between populations which share the same parental stock. Am. J. Hum. Biol. 13:718,720, 2001. © 2001 Wiley-Liss, Inc. [source]

Dynamical evolution of the mass function and radial profile of the Globular Cluster systems of the Milky Way and M87

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2008
J. Shin
Abstract Evolution of the mass function (MF) and radial distribution (RD) of the globular cluster (GC) systems of the Milky Way and M87 are calculated using an advanced and realistic Fokker-Planck (FP) model that considers dynamical friction, disk/bulge shocks, and eccentric cluster orbits. We perform hundreds of FP calculations with different initial cluster conditions, and then search a wide parameter space for the best-fit initial GC MF and RD that evolves into the observed present-day GC MF and RD. By allowing both MF and RD of the initial GC system to vary, we find that in case of the Milky Way, our best-fit models have a higher peak mass for a log-normal initial MF and a higher cutoff mass for a powerlaw initial MF than previous estimates. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

An extensive study of dynamical friction in dwarf galaxies: the role of stars, dark matter, halo profiles and MOND

Compound-specific stable carbon isotope ratios (,13C values) of the halogenated natural product 2,3,3,,4,4,,5,5,-heptachloro-1,-methyl-1,2,-bipyrrole (Q1)

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 20 2006
Walter Vetter
Compound-specific isotope analysis using gas chromatography interfaced to isotope ratio mass spectrometry (GC/IRMS) was applied for the determination of ,13C values of the marine halogenated natural product 2,3,3,,4,4,,5,5,-heptachloro-1,-methyl-1,2,-bipyrrole (Q1). The ,13C value of a lab-made Q1 standard (,34.20,±,0.27,) was depleted in 13C by more than 11, relative to the residues of Q1 in dolphin blubber from Australia and skua liver from Antarctica. This clarified that the synthesized Q1 was not the source for Q1 in the biota samples. However, two Australian marine mammals showed a large variation in the ,13C value, which, in our experience, was implausible. Since the GC/IRMS system was connected to a conventional ion trap mass spectrometer by a post-column splitter, we were able to closely inspect the peak purity of Q1 in the respective samples. While the mass spectra of Q1 did not indicate any impurity, a fronting peak of PCB 101 was identified in one sample. This interference falsified the ,13C value of the respective sample. Once this sample was excluded, we found that the ,13C values of the remaining samples, i.e. liver of Antarctic brown skua (,21.47,±,1.47,) and blubber of Australian melon-headed whale (,22.80,±,0.33,), were in the same order. The standard deviation for Q1 was larger in the skua samples than in the standard and the whale blubber sample. This was due to lower amounts of skua sample available. It remained unclear if the Q1 residues originate from the same producer and location. Copyright © 2006 John Wiley & Sons, Ltd. [source]