Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CHROMATOGRAPHY”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 469 records · Page 26Linked to original sources
PubMed1984

[Comparative studies of partial amino acid sequences of prolamins and glutelins from various cereals. VI. Anion exchange chromatography of peptide fractions obtained by cation exchange chromatography].

The main peptide fractions obtained from prolamins and glutelins of wheat, rye, barley, and corn by chymotryptic hydrolysis, gel filtration and cation exchange chromatography [1, 2] were further separated by anion exchange chromatography. The amino-acid compositions of the peptides obtained from wheat, rye and barley prolamins are closely related. Typical compositions are Glx greater than 44, Pro greater than 28, and Phe greater than 7 mol-%. The peptide fractions from corn prolamine are different (Glx greater than 20, Leu greater than 20, Ala greater than 12, Pro greater than 10 mol-%). The peptide fractions from wheat, rye and barley glutelins are less similar. Typical compositions are Glx greater than 30, Pro greater than 15, and Gly greater than 8 mol-%. Most of the fractions from corn glutelin contain many amino-acids with Glx, Leu, and Ala predominating. Wheat differs significantly from the other cereals because of the unique composition of some high molecular weight peptide fractions from glutelin, which are rich in Glx (greater than 49) and Gly (greater than 19 mol-%).

Amino Acid Sequence↗
PubMed1992

On-line coupled liquid chromatography-gas chromatography (LC-GC) and LC-LC-GC for detecting irradiation of fat-containing foods.

On-line coupled liquid chromatography-gas chromatography-flame ionisation detection (LC-GC-FID) enables efficient and unambiguous determination of irradiation for some fat-containing foods (e.g. meat). Other products, however, contain interfering components or are contaminated, e.g., with mineral oil. Since more selective detection by mass spectrometry has limited success, the determination was improved by a more selective isolation of some key components among the fat degradation products, e.g. the dienes or trienes, by LC-LC-GC-FID. Applications are shown for soup mixes, some spices, fish, and shrimps.

Alkanes↗
PubMed2005

Determination of selected polycyclic aromatic hydrocarbons and oxygenated polycyclic aromatic hydrocarbons in aerosol samples by high-performance liquid chromatography and liquid chromatography-tandem mass spectrometry.

Fine and ultrafine particles are probably responsible for numerous health effects, but it is still unclear whether and to what extent the particle itself or organic compounds adsorbed or condensed on the particle are responsible for the effects observed. One important class of particle-bound substances are the polycyclic aromatic hydrocarbons (PAH) and their oxygenated derivatives. To improve the tools used for chemical characterization of particulate matter analytical methods for the determination of PAH and oxygenated PAH in aerosol samples of different origin have been developed and optimized. PAH on high-volume filters and on soot aerosols were analyzed by using accelerated solvent extraction for extraction and high-performance liquid chromatography with fluorescence detection for separation and quantification. Total PAH concentrations were in the range 0.3-9.3 ng m(-3). For analysis of selected oxygenated PAH on high-volume filters a liquid chromatography-tandem mass spectrometric method was developed and optimized. Preliminary investigations showed that oxygenated PAH at pg m(-3) concentrations can be determined.

Aerosols↗
PubMed2005

Chromatography in silico, basic concept in reversed-phase liquid chromatography.

Basic phenomena in reversed-phase liquid chromatography have been quantitatively analyzed using a computational chemical calculation. Pyridine interacted with an ionized silica surface under neutral conditions. Alkyl-chain length affected the contact surface area with an analyte. Steric hindrance was demonstrated using a model graphitic carbon phase and unsaturated alkenes. Quantitative structure-retention relationships in reversed-phase liquid chromatography were demonstrated for phenolic compounds and acidic and basic drugs. The correlations between predicted and measured retention factors were satisfactory. Dissociation constants were derived from the atom partial charge and used to predict retention factors of partially ionized compounds.

Adsorption↗
PubMed2005

Biosynthesis of Cd-bound phytochelatins by Phaeodactylum tricornutum and their speciation by size-exclusion chromatography and ion-pair chromatography coupled to ICP-MS.

Cd-bound phytochelatins (Cd-PCs) have been synthesised by incubation of Phaeodactylum tricornutum cell cultures with Cd and purified by size-exclusion chromatography-UV-Vis. These complexes, which were identified in previous work, have now been used as model substances to develop and optimise ion-pair chromatography (IPC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS) for analysis of Cd-PCs. Subsequent analysis of samples taken from Silene vulgaris plants cultivated under heavy metal stress conditions revealed Cd signals but no Cd-PC signals. By use of isotopically enriched (116)Cd-PCs the sample preparation steps were verified to determine the stability of the analytes. We observed species transformation between Cd-PCs and other unidentified Cd complexes. Consequently, the kinetic and thermodynamic lability of Cd-PCs are decisive factors in their detection.

Cadmium↗
PubMed2006

Study of the microbiodegradation of terpenoid resin-based varnishes from easel painting using pyrolysis-gas chromatography-mass spectrometry and gas chromatography-mass spectrometry.

The alterations produced by microbiological attack on terpenoid resin-based varnishes from panel and canvas paintings have been evaluated using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and gas chromatography-mass spectrometry (GC-MS). The proposed methods include the on-line derivatisation of drying oils and diterpenoid resins using hexamethyldisilazane during pyrolysis and the application of methyl chloroformate as a derivatisation reagent for triterpenoid resins in GC-MS. Two types of specimens, consisting of model oil medium prepared from linseed oil and model spirit varnishes prepared from colophony and mastic resins dissolved in turpentine, have been used as reference materials. For a series of specimens upon which different genera of bacteria and fungi were inoculated and encouraged to grow, analyses indicated that no mechanisms that commonly occur during the attack of enzymes on drying oils and terpenoid biodegraders were observed to occur in the oil medium and varnishes studied. Thus, the degradation pathways observed in the performed trials usually occur as consequence of natural ageing. Specific trials consisting of the application of biocides to uninoculated colophony varnish resulted in the identification of processes that produce undesirable degradation of the varnish due to interactions between the biocide and the varnish components. Finally, the studied biocides--Biotin, New-Des and Nipagine--generally exhibited good inhibiting effects on the microorganisms studied, although some interesting differences were found between them regarding the application method and type of biocide.

Biodegradation, Environmental↗
PubMed1975

Monoamine metabolites and related compounds in human amniotic fluid: assay by gas chromatography and gas chromatography-mass spectrometry.

Some catecholamine metabolites and related compounds have been identified in amniotic fluid obtained by transabdominal amniocentesis at various stages of pregnancy, including 4-hydroxy-3-methoxymandelic acid, 4-hydroxy-3-methoxyphenylglycol, 4-hydroxy-3-methoxyphenylcetic acid, p-hydroxypheny lacetic acid, p-hydroxphenyllactic acid and N-benzoylglycine (hippuric acid). Analysis was by gas chromatography with electron capture detection and by gas chromatography-mass spectrometry. Two of these compounds were determined quantitatively, free 4-hydroxy-3-methoxphenylglycol and p-hydroxyphenllactic acid: the concentration of the former increased with advancing pregnancy and that of the latter tended to decrease. Conjugated 4-hydoxy-3-methoxyphenylglycol could not be determined with accuracy as appreciable amounts of the unconjugated compound were found in the snail extract used for enzymatic hydrolysis. Assay of 4-hydroxy-3-methoxyphenylglycol in amniotic fluid is likely to be of diagnostic importance in the prenatal diagnosis of congenital neuroblastoma. Although 4-hydroxy-3-methoxyphenylethanol, 3, 4-dihydroxymandelic acid and 3, 4-dihydroxyphenylacetic acid were specifically looked for in amniotic fluid, they could not be detected.

Amniocentesis↗
PubMed1993

Peculiarities of zone migration and band broadening in gradient reversed-phase high-performance liquid chromatography of proteins with respect to membrane chromatography.

The peculiarities of zone migration and band broadening in the reversed-phase gradient HPLC of proteins were investigated. In the isocratic mode a critical composition of the mobile phase was found at which all proteins regardless of their molecular mass migrate with equal velocity and have a capacity factor equal to the phase ratio (VP/V0), i.e., the same capacity factor as a marker of total accessible volume would have in steric exclusion chromatography. It is shown that steric exclusion conditions are never achieved in gradient HPLC. In the first (adsorption stage) of gradient elution where the separation takes place the velocity of a protein increases until it becomes equal to the velocity of the desorbing solvent front at a critical distance X0 from column entrance. Strong broadening is characteristic of this stage. In the second (critical) stage the protein travels the remaining distance (L-X0) with the velocity of the solvent. A definition of X0 is given allowing one very simple calculation of the minimum permissible column length as a function of gradient steepness, mobile phase velocity and protein adsorption parameter. When x = X0 the protein zone has the smallest dispersion. Making L < X0 is especially disadvantageous, as it leads to anomalous bandspreading. The theory of gradient HPLC was refined on this basis and the usefulness of this approach in high-performance membrane chromatography is demonstrated.

Adsorption↗
PubMed1995

Linear solvation energy relationships in micellar liquid chromatography and micellar electrokinetic capillary chromatography.

Linear solvation energy relationships (LSERs) were used to evaluate and characterize chemical interactions that influence retention behavior in micellar liquid chromatography (MLC) and micellar electrokinetic capillary chromatography (MEKC). High correlations were found between solutes' capacity factors in MLC and in MEKC, as well as binding constants to micelles and their solvatochromic parameters using two anionic surfactants, sodium dodecyl sulfate (SDS) and sodium cholate (SC), and one cationic surfactant, tetradecyltrimethylammonium bromide (C14TAB). Surprisingly, in the C14TAB MLC system capacity factor (k') vs. solvatochromic parameters gives better correlation than log k' vs. solvatochromic parameters, which is an opposite behavior to that observed in the SDS MLC system. The capacity factors in the C14TAB MLC system were characterized using LSERs with and without organic modifiers. It was found that the addition of a small amount of short-chain alcohols (e.g., 7% 2-propanol or 5% butanol) does not significantly change the high correlations between k' vs. solvatochromic parameters. The changes in the coefficients with the volume fraction of organic solvents were explained by comparing the differences in chemical natures between mobile phase and stationary phase. Stationary phase shows a significant effect on the chemical interactions in MLC through LSER study using a diphenyl column and a C8 column. LSERs were also used to characterize retention behavior in MEKC. High correlations between the logarithm of solutes' capacity factors and their solvatochromic parameters were observed for a group of 25 uncharged substituted aromatic compounds and polycyclic aromatic hydrocarbons with SDS and SC micelles. It was found that solutes' size and basicity are the two dominant factors that influence the migration behavior in MEKC.

Chromatography, Liquid↗
PubMed1995

Ion-pair chromatography and micellar electrokinetic capillary chromatography in analyzing beta-adrenergic blocking agents from human biological fluids.

Ion-pair chromatography (IPC) and micellar electrokinetic capillary chromatography (MECC) were used for the separation and determination of parent beta-blockers from human biological fluids. In both these techniques, N-cetyl-N,N,N-trimethylammonium bromide (CTAB) was used as a buffer additive. In IPC, CTAB was an ion-pair former, and in MECC it was a micelle-forming surfactant. The effectiveness of the IPC method using methanol-gradient elution and that of MECC were compared for drug-spiked serum and urine samples. Detection was performed with a diode-array detector in the IPC method and with a 214-nm filter in the MECC technique. In both methods a phosphate buffer (pH 7.0) was used. In MECC the buffer solution contained 10 mM CTAB, while in IPC the CTAB concentration was decreased from 7 to 4 mM during the separation when a methanol gradient was used. The study showed that the IPC technique performed better for bioanalyses than the high-performance MECC technique, since in MECC UV detection presented a problem because of the low sample concentration. However, in MECC sample preparation was less time-consuming, using hydrolyzation and protein precipitation and, unlike the IPC technique, it did not require any liquid-liquid extraction step.

Adrenergic beta-Antagonists↗
PubMed1996

Separation parameters via virtual migration distances in high-performance liquid chromatography, capillary zone electrophoresis and electrokinetic chromatography.

Among the various differential migration processes of separation, high-performance liquid chromatography (HPLC) and capillary zone electrophoresis (CZE) have emerged as the two major high-performance analytical techniques for separation of complex biological substances. In both HPLC and CZE with electroendoosmotic flow, the differential migration process can be divided into a separative component, which involves selective interactions with the stationary phase or differences in the electrophoretic migration velocities, and a non-separative component representing migration by convection that does not contribute directly to separation. The introduction of virtual migration distances leads to an additivity relationship for the two components that is applicable to both of the above techniques and facilitates the recognition of the underlying similarities as well as the expression and comparison of the various separation parameters. Examination of the key migration parameters led to the characterization and the classification of the various modes of CZE with electroendoosmotic flow. The treatment was extended to the analysis of capillary electrochromatography and micellar electrokinetic chromatography; two hybrid processes which exhibit features borrowed from HPLC and CZE. The use of virtual migration distances also led to a consistent and unified description of the characteristic parameters of these separation systems.

Chromatography, High Pressure Liquid↗
PubMed1991

Comparison of ion-exchange chromatography, isoelectric precipitation and reversed-phase high-performance liquid chromatography for the separation of individual cardiac myosin light chains.

Three modified procedures for the separation of cardiac myosin light chains are carefully compared. Ion-exchange chromatography gives a purified cardiac myosin light chain 1, whereas light chain 2 is always contaminated by light chain 1. Reversed-phase high-performance liquid chromatography gives the best resolution of these light chains and needs only 20 min for each run. However, it requires pure preparation of myosin light chains before separation. Isoelectric precipitation is the simplest procedure and suitable for large quantities of material. Although it gives the highest yield the separation is not adequate. A modified and rapid procedure for the isolation of cardiac and skeletal total myosin light chains is also presented.

Chromatography, Ion Exchange↗
PubMed1992

Determination of ceftazidime in dolphin serum by liquid chromatography with ultraviolet-visible detection and confirmation by thermospray liquid chromatography-mass spectrometry.

A simple and sensitive liquid chromatographic method has been developed for the determination of therapeutic levels of ceftazidime in dolphin serum. The method involved an ultrafiltration of diluted serum with an equal amount of acetonitrile-ethanol-water (40:40:20, v/v/v) through a 10,000 daltons molecular mass cut-off filter. Separation of ceftazidime from the other serum components was performed by ion-paired (dodecanesulfonate) liquid chromatography using a reversed-phase column eluted with acetonitrile-water solution. The ultraviolet absorbance of the column effluent was monitored in the 200-340 nm range of a photodiode-array detector or at 258.8 nm on a variable-wavelength ultraviolet-visible detector. Recoveries of ceftazidime from dolphin serum spiked with 20 and 2 micrograms/ml were 92.9 and 91.1% with coefficients of variation of 5.5 and 5.7%, respectively. A correlation coefficient of 0.9994 occurred with ceftazidime in aqueous solutions (n = 6, in duplicates). The limit of detection for this antibiotic was estimated to be approximately 50 ppb (ng/ml). The unbound ceftazidime concentrations in dosed dolphin serum were determined to calculate the protein bindings of this antibiotic which yielded 32 +/- 2%. The ceftazidime peak identity in dosed dolphin serum was confirmed by thermospray liquid chromatography-mass spectrometry. The thermospray mass spectrum of ceftazidime exhibited only the fragment ions, involving the opening of the beta-lactam ring, at m/z 237, 255 and 315 when positive-ion detection mode was employed and the fragment ions at m/z 235, 253 and 313 when negative-ion detection mode was used.

Animals↗
PubMed1993

Determination of nicotine and two major metabolites in serum by solid-phase extraction and high-performance liquid chromatography, and high-performance liquid chromatography-particle beam mass spectrometry.

A rapid and selective assay of nicotine, cotinine and trans-3'-hydroxycotinine in human serum, based on high-performance liquid chromatography with UV detection has been developed. The compounds were subjected to solid-phase extraction, using Extrelut 1 cartridges. Recoveries were ca. 95% for nicotine, 90% for cotinine and 50-55% for trans-3'-hydroxycotinine. The limit of quantitation observed with this method was 10 ng/ml for nicotine and 5 ng/ml for each of the metabolites. The compounds were also identified using high-performance liquid chromatography with particle beam mass spectrometry, to confirm their presence in human serum.

Chromatography, High Pressure Liquid↗
PubMed1996

Quality control in the determination of cortisol in plasma/serum by using, on every sample, two different three-step separation methods including ultrafiltration, restricted-access high-performance liquid chromatography and reversed-phase high-performance liquid chromatography, and contrasting results to immunoassays.

Tests of HPLC columns with restricted access, polymer covered alumina, polymer, and different ODS phases showed that base-acid compatible ODS columns gave the best peak shapes of cortisol, internal standard, as well as of plasma/serum (P/S) matrix components. Further trials with cortisol in P/S showed that three separation steps were essential in order to obtain chromatographic data which were superior to immunoassay data. Also, sufficient confidence in results required determination of each sample with two newly developed separation methods: (a) pre-separation with a restricted access column, concentration of the desired cut with a 20 mm base-acid compatible ODS column, and analysis with a 250 mm column filled with the same ODS; (b) pre-separation with an ultrafilter followed by the last two steps in (a). For detection UV was preferred over fluorescence. This twin multistep chromatography showed that immunoassays were very treacherous in that they produced a spectrum of results ranging from good to untenable without any warning whatever about functionality. The measurement of official controls, with reference values derived via gas chromatography-isotope dilution mass spectrometry, also demonstrated the superiority of the double HPLC method.

Chromatography, High Pressure Liquid↗
PubMed2004

Complementary use of gas chromatography-mass spectrometry, gas chromatography-atomic emission detection and nuclear magnetic resonance for identification of pharmaceutically related impurities of unknown structures.

The complementary use of gas chromatography-mass spectrometry (GC-MS), gas chromatography-atomic emission detection (GC-AED) and nuclear magnetic resonance (NMR) spectroscopy is demonstrated by the identification of four major by-products in a sample from an exploratory attempt to synthesise 1.3-dichloro-5-(difluoromethoxy)benzene. GC-MS was used for straightforward identification of the target compound and one of the impurities. By employing GC-AED, the sample was screened for heteroatoms in the analysed molecules and determination of the partial empirical formula of one sample component was carried out. The combined spectroscopic data obtained from the MS and AED experiments facilitated structure elucidation of two of the additional by-products. Finally, identification of the last unknown component could be obtained by combining spectral information from GC-MS, GC-AED and NMR data acquired after isolation of the impurity from the sample.

Gas Chromatography-Mass Spectrometry↗
PubMed2004

Monolayer-protected gold nanoparticles as an efficient stationary phase for open tubular gas chromatography using a square capillary model for chip-based gas chromatography in square cornered microfabricated channels.

The application of a dodecanethiol monolayer-protected gold nanoparticle (MPN) stationary phase within a microchannel environment was explored using a square capillary column as a model for high-speed, microfabricated gas chromatography (microGC). Successful deposition and evaluation of a dodecanethiol MPN phase within a 1.3 m long, 100 microm x 100 microm square capillary is reported. The thickness of the MPN phase was evaluated using SEM analysis. An average thickness of 15 nm along the capillary walls was determined. While the film depth along the walls was very uniform, the corner depths were greater with the largest observed depth being 430 nm. Overall, an efficient chromatographic system was obtained with a minimum reduced plate height, h(min), of 1.2 for octane (k = 0.22). Characterization of the MPN column was completed using four compound classes (alkanes, alcohols, ketones, and aromatics) that were used to form a seven-component mixture with a 2-s separation. A mixture consisting of a nerve agent simulant in a sample containing analytes that may commonly interfere with detection was also separated in only 2 s, much faster than a similar separation previously reported using a microGC system requiring 50 s. A comparison of the MPN stationary phase to phases employed in previously reported microGC systems is also made. Application of the square capillary MPN column for a high-speed separation as the second column of a comprehensive 2-D gas chromatography system (GC x GC) was also explored.

Chromatography, Gas↗
PubMed2004

Determination of epichlorohydrin by sulfite derivatization and ion chromatography: characterization of the sulfite derivatives by ion chromatography-mass spectrometry.

This work is an upgrade of a previously developed method (J. Chromatogr. A 884 (2000) 251] for epichlorohydrin determination by ion chromatography (IC) and conductivity detection. Here, an ion chromatography-mass spectrometry (IC-MS) coupling has been employed for the separation and the identification of products of epichlorohydrin when reacted with the nucleophilic agent SO3(2-). The high capacity column (IonPac AS11-HC) used for separation provided good resolution. This allowed evaluation of the IC behavior and mass spectrometric identification of epichlorohydrin sulfite derivatives. By using atmospheric pressure interfaces (ESI and APCI) the following species were tentatively identified: 2,3-dihydroxy-1-propanesulfonic, 2,3-epoxy-1-propanesulfonic,1,3-dihydroxy-2-propanesulfonic and 3-oxetanesulfonic acids and 2-hydroxy-1,3-propanedisulfonic acid (or its isomer 3-hydroxy-1,2-propanedisulfonic acid). The study showed that chlorine atoms are displaced from epichlorohydrin during the reaction, while mass spectrometry confirmed that none of the products formed contains chlorine atoms.

Chromatography, Liquid↗