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 1,099 records · Page 61Linked to original sources
PubMed1992

Separation of (R)- and (S)-naproxen using micellar chromatography and an alpha 1-acid-glycoprotein column: application for chiral monitoring in human liver microsomes by coupled-column chromatography.

A column-switching system for fast determination of (R)- and (S)-naproxen in liver microsomes has been developed. The centrifuged sample was injected directly onto a pre-column with octadecylcoated silica. The retained analytes were then directed to an alpha 1-AGP column using a mobile phase composed of phosphate buffer (pH 6.5), dimethylocytylamine (30 mM) and the nonionic surfactant, Tween 20 (40 g/l). The method gave high absolute recoveries and good repeatabilities: 99.6% (1.7% relative standard deviation) and 94.9% (2.4% R.S.D.) for the (R)- and (S)-naproxen, respectively. The use of a surfactant in combination with an aliphatic amine in the mobile phase involves reduced retention times with retained enantioselectivity. Furthermore, the presence of the surfactant makes it possible to inject biological samples directly into the chromatographic system.

Chemistry Techniques, Analytical↗
PubMed1985

Quantitative analysis of veralipride in plasma and urine by gas chromatography-mass spectrometry and gas chromatography with flame-ionization detection.

A highly sensitive and selective quantitative assay for unchanged veralipride has been developed. The compound is extracted from alkalized samples (plasma or urine) with dichloromethane and converted to its trimethylated derivative by reaction with trimethylanilinium hydroxide. The reaction mixture is then chromatographed on a 3% OV-1 column. Trimethylated derivatives of plasma samples were assayed by selected-ion monitoring in the chemical-ionization mode and quantified by comparing the intensity of the quasi-molecular ion m/z 426 (M + H) with the intensity of the corresponding ion from trideuterated internal standard, m/z 429 (M + H). Flame-ionization detection was used for the assay of urine samples. The peak height ratio of trimethylated veralipride over trimethylated sulpiride, the internal standard, was used for quantitation of urine samples. A relative standard deviation of less than 10% was found when quantifying 10 ng/ml veralipride in plasma or 1 microgram/ml in urine.

Capsules↗
PubMed1987

Application of high-performance liquid chromatography and thermospray high-performance liquid chromatography-mass spectrometry to the analysis and identification of 2',3'-dideoxyadenosine and its metabolite in biological media.

Reversed-phase high-performance liquid chromatographic (HPLC) procedures are described for determining the stability of 2',3'-dideoxyadenosine (DDA) in biological fluids at therapeutic dosages. The validated methodology uses both direct injection and solid-phase extraction techniques. Deamination of DDA to 2',3'-dideoxyinosine (DDI) in plasma by adenosine deaminase was monitored by HPLC, and the identification of DDI verified by thermospray HPLC-mass spectrometry. This methodology should prove useful in future studies concerning the stability and metabolism of dideoxynucleosides.

Adenosine Deaminase↗
PubMed1994

Determination of the enantiomers of nisoldipine in human plasma using high-performance liquid chromatography on a chiral stationary phase and gas chromatography with mass-selective detection.

A method is described that combines chiral HPLC and off-line GC with mass-selective detection for the quantitation of the enantiomers of nisoldipine [(+/-)-I] in human plasma. An isotope-labelled internal standard [nine-fold deuterated (+/-)-I] is used throughout the assay. The limit of quantification is 0.1 microgram/l for each enantiomer. Data on the precision, accuracy and selectivity of the method are presented. Enantioselective analysis was performed in subjects receiving the racemic drug in tablet form. In healthy volunteers the maximum concentration and the area under the curve of the pharmacologically more active (+)-enantiomer were greater by 9-fold and 13-fold, respectively, compared to those of the (-)-enantiomer. In elderly hypertensive patients plasma concentrations of (+)-I were ca. five times as high as those of the (-)-enantiomer. Stereoselectivity was not affected by hepatic impairment. After intravenous administration of (+/-)-I there were no relevant differences between the plasma concentrations of the enantiomers.

Adult↗
PubMed1994

Investigation of meperidine and its metabolites in urine of an addict by gas chromatography-flame ionization detection and gas chromatography-mass spectrometry.

A gas chromatographic method with flame ionization detection (FID) for the quantitative analysis of meperidine and mass spectrometry (MS) for the qualitative analyses of meperidine and its metabolites in urine was established. Meperidine, normeperidine and acetyl normeperidine in urine were extracted with ether. Free and conjugated meperidinic and normeperidinic acids in urine, which are hydrophillic, were hydrolyzed by acid, esterified with methanol and derivatized with acetic anhydride. Meperidine and its four metabolites were identified by GC-MS. Meperidine was measured by GC-FID during 72 h after intramuscular administration of meperidine to an addict.

Biotransformation↗
PubMed1991

Use of stop-flow oxalate ester chemiluminescence as a means to determine conditions for high-performance liquid chromatography chemiluminescence detection of retinoids using normal-phase chromatography.

Stop-flow chemiluminescence (CL) has been used to determine the conditions necessary for the oxalate ester CL detection of selected retinoids after separation by normal-phase HPLC. Also, the detection of the selected retinoids by bis(2,4,6-trichlorophenyl) oxalate (TCPO)-hydrogen peroxide (H2O2) chemiluminescence and fluorescence (FL) are compared. Stop-flow CL was performed on a prototype uit from High-Tech Scientific, Ltd (Salisbury, UK). Detection limits were determined for retinyl palmitate, retinyl acetate, retinol, etretinate, acitretin and tretinoin, after separation on a YMC PVA-sil, 25 cm x 4.6 mm column using hexane-tetrahydrofuran-acetic acid (75:25:0.01, v/v/v) as eluent at 1.5 ml min-1. A Schoeffel 970 detector was used for both CL and FL detection. Detection by FL was determined with lambda ex 355 nm and lambda em greater than 418 nm. CL detection was performed with the deuterium lamp off and no emission filter. CL was induced by mixing the reagents post-column. Pump A--hexane--THF--AcOH (75:25:0.01, v/v/v) at 1.5 ml min-1, pump B--70 mM TCPO in THF at 0.5 ml min-1, pump C--THF--50% aq H2O2 (75:25, v/v) 1.0 mg ml-1 imidazole at 1.0 ml min-1.

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

Reversed-phase liquid chromatography of the opioid peptides. 3. Development of a microanalytical system for opioid peptides involving microbore liquid chromatography, post-column derivatization and laser-induced fluorescence detection.

A microanalytical system has been developed for the determination of peptides in small samples. Naphthalene-2,3-dicarboxaldehyde-beta-mercaptoethanol (NDA-BME) was used as the labelling reagent system as an alternative to NDA-cyanide (NDA-CN) because of the faster labelling when CN was replaced by a thiol. The fluorescence characteristics of the NDA-thiol adducts, N-substituted 1-alkylthiobenz[f]isoindoles (TBIs), were found to be different from the previously described cyanobenz[f]isoindole (CBIs) adducts formed by the reaction of primary amines with NDA-CN. The excitation maximum of the TBI adducts was at 460 nm, which was closer to the 457.9 nm argon-ion laser line, than the 440-nm maximum of the CBI adduct. The limit of detection for leucine enkephalin was 36 fmol (S/N = 3) and linearity was proven for greater than 2 orders of magnitude, from 45 fmol to 9 pmol for an injection volume of 60 nl. The detectability was limited by the high background noise produced by the post-column derivatization system. The utility of the system was demonstrated for the analysis of methionine enkephalin and its potential oxidation products, using leucine enkephalin as a suitable internal standard.

Chromatography, Liquid↗
PubMed2004

Analysis of aspartyl peptide degradation products by high-performance liquid chromatography and high-performance liquid chromatography-mass spectrometry.

A reversed-phase HPLC method for the analysis of degradation products of the model aspartyl tripeptides Phe-Asp-GlyNH2 and Gly-Asp-PheNH2 after incubation at pH 2 and 10 was developed. Most of the compounds could be separated with a gradient of acetonitrile in water containing 0.1% trifluoroacetic acid. Resolution of the isomeric pairs L-Phe-alpha-L-Asp-GlyNH2/L-Phe-beta-L-Asp-GlyNH2 and L-Phe-alpha-D-Asp-GlyOH/L-Phe-beta-D-Asp-GlyOH was achieved with a gradient of acetonitrile in phosphate buffer, pH 5.0. Under acidic conditions the major degradation pathway was cleavage of the peptide backbone amide bonds yielding dipeptides and amino acids, C-terminal deamidation as well as formation of succidinimyl peptides. At alkaline pH both deamidation of the C-terminal amide as well as isomerization and concomitant enantiomerization of Asp were observed. The peaks were identified both by reference substances and by online electrospray mass spectrometry. The results were compared to a previous developed capillary electrophoresis method. Diastereomeric pairs ofpeptides that could not be separated by capillary electrophoresis were resolved by HPLC while the separation of corresponding pairs of alpha- and beta-Asp peptides was not always achieved by HPLC in contrast to capillary electrophoresis illustrating that both techniques can be complimentary in peptide analysis.

Aspartic Acid↗
PubMed2004

Characterization of three agave species by gas chromatography and solid-phase microextraction-gas chromatography-mass spectrometry.

Steam distillation (SD) extraction-solid-phase microextraction coupled to GC-MS was developed for the determination of terpenes and Bligh-Dyer extraction-derivatization coupled with GC for the determination of fatty acids such as ethyl esters were used. It was found that the three different Agave species have the same profile of fatty acids; the quantity of these compounds is different in each Agave variety. On the other hand, different terpenes were identified in the three Agave plants studied: nine in A. salmiana, eight in A. angustifolia and 32 in A. tequilana Weber var. azul.

Agave↗
PubMed2004

Combined use of liquid chromatography-nuclear magnetic resonance spectroscopy and liquid chromatography-mass spectrometry for the characterization of an acarbose degradation product.

Directly coupled LC-MS and LC-NMR were applied to identify and structurally characterize an acarbose degradation product A in acidic media. A comparative analysis of the stop-flow LC-NMR (1H and TOCSY) and LC-MS data provided evidence that A is structurally related to acarbose, differing from the parent compound in a number of subunits present in the molecule. Spectral analysis revealed that A was the alpha-glucosidase inhibitor amylostatin XG. Complementary information obtained from the two methods led to the structural elucidation of A which was later corroborated by high-resolution NMR spectroscopy of the isolated molecule.

Acarbose↗
PubMed2004

Transforming chiral liquid chromatography methodologies into more sensitive liquid chromatography-electrospray ionization mass spectrometry without losing enantioselectivity.

LC-electrospray ionization (ESI) MS conditions were optimized for the individual chiral separation of 19 compounds of pharmaceutical interest using the macrocyclic glycopeptide-based chiral stationary phases in both polar organic and reversed-phase modes (RPM). The influence of mobile phase composition and MS additive type on sensitivity was investigated for all classes of compounds tested. Compounds with amine or amide groups were efficiently separated, ionized, and detected with the addition of 0.1% (w/w) ammonium trifluoroacetate to the solvent system in either the reversed-phase or polar organic mode (POM). Macrocyclic glycopeptide coupled column technology was initially used to screen all chiral compounds analyzed. Baseline resolution of enantiomers was then achieved with relatively short retention times and high efficiencies on Chirobiotic T, Chirobiotic V or Chirobiotic R narrow bore chiral stationary phases. The polar organic mode offered better limits of detection (as low as 100 pg/ml) and sensitivity over reversed-phase methods. An optimum flow-rate range of 200-400 microl/min was necessary for sensitive chiral LC-ESI-MS analysis.

Chromatography, Liquid↗
PubMed2004

Determination of benzoyl peroxide and benzoic acid in wheat flour by high-performance liquid chromatography and its identification by high-performance liquid chromatography-mass spectrometry.

An HPLC method on C18 column using a gradient mobile phase is proposed for the separate determination of residual benzoyl peroxide (BP) and benzoic acid (BA) in flour and wheat products. The recoveries obtained were quite excellent, from 96.0 to 99.3% for BP added to the flour, and 91.3% for BA added to the flour. Analysis of 10 samples of commercial foods such as flour and wheat products, detected 0.7 microg/g of BP in imported noodles. Furthermore, we successfully verified the existence of BP by LC-MS. These methods are simple and reliable for determination and verifying the amount of BP and BA in foods since now the use of BP as a food additive is permitted in many countries.

Benzoic Acid↗
PubMed2004

Quantification of ligustilides in the roots of Angelica sinensis and related umbelliferous medicinal plants by high-performance liquid chromatography and liquid chromatography-mass spectrometry.

A reversed phase high-performance liquid chromatographic method was developed for quantifying E-ligustilide (1) and Z-ligustilide (3) in the roots of Angelica sinensis (Oliv.) Diels with confirmation using UV, atmospheric pressure chemical ionisation (APCI) MS and APCI-MS-MS techniques. Based on the UV spectra of compounds 1, E-butylidenephthalide (2), 3 and Z-butylidenephthalide (4), the absorption at 350 nm was chosen as measuring wavelength in which baseline separation of compounds 1 and 3 could be obtained but avoided the interference of compounds 2 and 4. The identity of compounds 1 and 3 in samples were unambiguously determined by the respective quasi-molecular ions ([M+H]+) in APCI-MS. According to the stability data, acetonitrile was chosen for the preparation of standard solutions in order to minimize the isomerization of compound 3. Compounds 1 and 3 were qualitatively and quantitatively analyzed in seven samples of the roots of Angelica sinensis (Oliv.) Diels, Angelica acutiloba Kitagawa, Angelica acutiloba Kitagawa var. sugiyamae Hikino and the rhizome of Ligusticum chuanxiong Hort. Analysis of an extract from a sample root of Angelica gigas Nakai using LC-MS for the first time could not detect the presence of ligustilide in this herb. The overall analytical procedure is rapid and reproducible which is considered suitable for quantitative analysis of large number of samples.

Angelica sinensis↗
PubMed2004

Comparative study of analytical methods involving gas chromatography-mass spectrometry after derivatization and gas chromatography-tandem mass spectrometry for the determination of selected endocrine disrupting compounds in wastewaters.

Two GC-MS methods, based on the application of N,O-bis(trimethylsilyl)trifluoroacetamide-derivatization-GC-MS (selected-ion monitoring) and GC-MS-MS without derivatization, respectively, were optimised and applied to the determination of a group of five selected endocrine disrupting compounds (EDCs) in wastewaters. Both methods included solid-phase extraction with Oasis HLB cartridges allowing an enrichment factor for wastewater samples of 100-fold. The investigated EDCs were estrone, 17beta-estradiol, 17alpha-ethynylestradiol, 4-tert-octylphenol and bisphenol A. Results obtained from the validation studies yielded comparable results in both cases. Recoveries in spiked wastewaters at 50 ng/l were higher than 90% for all the compounds, except for 4-tert-octylphenol (75%). Repeatability and reproducibility were adequate, varying from 1.6 to 14%, except for estrone which reproducibility was 28% when the derivatization-GC-MS method was applied. Limits of detection calculated ranged from 2.5 to 27.5 ng/l with differences between both methods from 1.1 (estrone) to 10.4 (bisphenol A) times. Both methods were successfully applied to the analysis of the target compounds in sewage treatment plant influents and effluents. Traces of bisphenol A, 4-tert-octylphenol, estrone and 17beta-estradiol were detected at concentration levels ranging from 13.3 to 1105.2 ng/l.

Endocrine Glands↗
PubMed2005

Detection of Nepsilon-monomethyllysine using high-performance liquid chromatography and high-performance liquid chromatography-mass spectrometry.

Nepsilon-Monomethyllysine was identified in the serum, urine, brain, and liver samples of rats treated per os with L-deprenyl. The identification procedure included reaction with Fmoc chloride, clean-up, and analysis using HPLC-UV-MS. Oral administration of (-)-N-14C-methyl-N-propynyl(2-phenyl-1-methyl)ethylammonium hydrochloride L-deprenyl) to rats resulted in transfer of the radiolabelled methyl group to the Nepsilon-amino group of the endogenous lysine. The radiolabelled Nepsilon-monomethyllysine was urinary eliminated together with the other radiolabelled deprenyl metabolites, such as deprenyl-N-oxide and methamphetamine. The presence of Nepsilon-monomethyllysine has also been traced, and its concentrations were compared in the serum, liver and brain of rats subjected to L-deprenyl treatment. Methyl group transfer from the L-deprenyl to endogenous compounds; and the urinary elimination of their products may offer a vital way to eliminate or to decrease the degree of drug transmethylation to the lysine constituents of blood vessels' proteins.

Animals↗
PubMed2005

Study of Burseraceae resins used in binding media and varnishes from artworks by gas chromatography-mass spectrometry and pyrolysis-gas chromatography-mass spectrometry.

In the present work, a study attempting to characterize the Manila elemi and Mexican copal resins from the Burseraceae family, which are used as components of varnishes and binding media of artworks, has been carried out. A new GC-MS method involving the use of methyl chloroformate as derivatisation reagent has been proposed. A second method which uses pyrolysis-GC-MS and hexamethyldisilazane as derivatization reagent has also been applied. Characterization of the main components of the mono-, sesqui- and triterpenoid fractions occurring in the raw materials has been achieved. Both alpha- and beta-amyrin have been established as the major triterpenoid compounds occurring in these resins together with hop-22(29)-en-3beta-ol, found only in the Mexican copal. Artificially aged samples of Manila elemi and Mexican copal have also been analysed in order to study the stability of the triterpenoid components of the resins and their possible use as marker molecules. The results obtained indicate that these molecules, in particular, alpha- and beta-amyrin undergo oxidation processes during both artificial and natural ageing. Nevertheless, hop-22(29)-en-3beta-ol could be selected as marker compound for Mexican copal. The proposed methods of analysis have been applied to real paint samples extracted from paintings in which Mexican copal was present as the main component of an "oleoresin" binding medium to assess their ability for identifying this product when used in artworks. Satisfactory identification of this resin is obtained by means of GC-MS whereas Py-GC-MS provides, in general, weaker signals for the components of the resin. Additionally, the influence of the pigments present in real samples on the resin ageing process has been considered.

Burseraceae↗
PubMed2006

Multiresidue liquid chromatography tandem mass spectrometry determination of 52 non gas chromatography-amenable pesticides and metabolites in different food commodities.

A multiresidue method is developed for the screening, quantification and confirmation of 43 pesticides, belonging to different chemical families of insecticides, acaricides, fungicides, herbicides and plant growth regulators, and 9 pesticide metabolites in four fruit and vegetable matrices. Pesticide residues are extracted from the samples with MeOH:H2O (80:20, v/v) 0.1% HCOOH, and then a cleanup step using OASIS HLB SPE cartridges is applied. The SPE eluate is concentrated and the final volume adjusted to 1 mL with MeOH:H2O (10:90, v/v) before injection into LC-MS/MS. Analyses are performed using electrospray ionization (ESI) and triple quadrupole (QqQ) analyzer. The method has been validated based on the SANCO European Guidelines for representative samples that were chosen to study the influence of different matrices: high water content (tomato), high acidic content (lemon), high sugar content (raisin) and high lipidic content (avocado). Special attention has been given to minimize the degradation of some pesticides into their metabolites and the losses observed in the evaporation step. Under the optimized conditions, the recoveries were, with a few exceptions, in the range 70-110% with satisfactory precision (CV < or = 15%). The quantification of analytes was carried out using the most sensitive transition for every compound and by "matrix-matched" standards calibration. The method can be used for the accurate determination of 52 pesticides and metabolites in one single determination step at the 0.01 mg/kg level. Confirmation of residues detected in samples is performed by an independent injection into the LC-MS/MS system by acquiring additional MS/MS transitions to that used for quantification. The acquisition of the highest number of available transitions is suggested for unequivocal confirmation of the analyte.

Chromatography, High Pressure Liquid↗
PubMed2006

Determination of ofloxacin, norfloxacin, and ciprofloxacin in sewage by selective solid-phase extraction, liquid chromatography with fluorescence detection, and liquid chromatography--tandem mass spectrometry.

A solid-phase extraction (SPE) and liquid chromatographic (LC) method was developed for the determination of selected fluoroquinolone (FQ) drugs including ofloxacin, norfloxacin, and ciprofloxacin in municipal wastewater samples. Extraction of the FQs was carried out with a weak cation exchanger SPE cartridge, the Oasis WCX. The cartridge was washed with water and methanol as a cleanup before the FQs were eluted by a mixture of methanol, acetonitrile, and formic acid. Separation of the FQs was achieved by using a Zorbax SB-C8 column under isocratic condition at a flow rate of 0.2mL/min. Recoveries of the FQs in spiked final effluent samples were between 87 and 94% with a relative standard deviation of less than 6%. Several techniques have been evaluated for the detection of FQs in sewage extracts; they included fluorescence detection and electrospray ionization (ESI) mass spectrometry using either mass-selective detection or tandem mass spectrometry (MS/MS). When they were applied to sewage influent and effluent samples, the LC-MS/MS technique operating in the multiple reaction monitoring (MRM) mode proved to be best suited for the determination of FQs in sewage samples as it provided the highest sensitivity (limit of quantification 5ng/L) and selectivity. The observation of signal suppression (matrix effect) for some FQs in ESI LC-MS and LC-MS/MS is discussed and a solution is proposed. The three FQs were detected in all the sewage samples tested in this work, with median concentrations between 34 and 251ng/L.

Chromatography, Liquid↗