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 829 records · Page 46Linked to original sources
PubMedDate not supplied

Micellar electrokinetic capillary chromatography combined with immunoaffinity chromatography for identification and determination of dexamethasone and flumethasone in equine urine.

A capillary electrophoresis technique was developed for the separation of synthetic glucocorticoids and the determination of dexamethasone and flumethasone in horse urine. Pretreatment of the sample using a dexamethasone affinity column resulted in low background that enabled the authors to detect levels as low as 1.1 ng/mL and 2.7 ng/mL for dexamethasone and flumethasone in horse urine, respectively. The developed method was used to detect dexamethasone in horse urine samples after the injection of a therapeutic dose of dexamethasone for up to 12 hr postinjection. The optimum conditions for capillary electrophoresis and dexamethasone elution from the affinity column are described.

Animals↗
PubMed1984

Quantitative analysis of trimethobenzamide hydrochloride by ion-pair column chromatography and semiquantitative analysis of 3,4,5-trimethoxybenzoic acid by thin-layer chromatography.

An ion-pair column chromatographic/UV spectrophotometric method for assaying trimethobenzamide hydrochloride in capsules and injections is presented, as well as a method for the detection of 3,4,5- trimethoxybenzoic acid in trimethobenzamide hydrochloride bulk drug and dosage forms. Results obtained by the USP XX, Pharmacopeial Forum, and ion-pair column assay procedures are compared, and results of a collaborative study of the proposed assay and impurity detection methods are presented.

Benzamides↗
PubMed1984

Evaluation of high-performance liquid chromatography and gas chromatography for quantitation of dextromethorphan hydrobromide in cough-cold syrup preparations.

A rapid and sensitive high-performance liquid chromatographic (HPLC) procedure is described for the analysis of the antitussive dextromethorphan hydrobromide in several cough-cold syrup preparations and compared with a gas chromatographic (GC) procedure. In the HPLC procedure, the active ingredient is analyzed as the hydrobromide salt by dilution in the mobile phase and separation on a reverse-phase cyano column. In the GC method, the active ingredient is analyzed as the free base, in which an aqueous solution of the antitussive is made alkaline and extracted with dichloromethane before injection onto the GC column. Excellent resolution of the antitussive agent was obtained by both systems; however, the HPLC assay is preferred for routine analysis (RSD 1%), as compared with the GC assay (RSD 4%).

Chromatography, Gas↗
PubMed1985

Determination of indeloxazine in plasma by liquid chromatography and gas chromatography-mass spectrometry.

Two methods have been developed for the quantitative determination of indeloxazine, a cerebral activator, in plasma by HPLC or GC-MS. After addition of viloxazine as the internal standard, indeloxazine was extracted from alkalinized plasma. In the HPLC method, the plasma extract was treated with 5-dimethylamino-1-naphthalenesulfonyl chloride and analyzed by HPLC with fluorescence detection. In the GC-MS method, the two plasma compounds were converted to their pentafluoropropionyl derivatives for selected-ion monitoring. The limits of detection were 5 and 2 ng/mL for the HPLC and GC-MS methods, respectively. When plasma samples obtained by giving indeloxazine hydrochloride to volunteers were analyzed by the two methods, good correlation between the data was obtained (r = 0.9901).

Antidepressive Agents↗
PubMed1987

Determination of (+)- and (-)-nilvadipine in human plasma using chiral stationary-phase liquid chromatography and gas chromatography-mass spectrometry, and a preliminary pharmacokinetic study in humans.

A stereoselective and sensitive method for the determination of nilvadipine, a new dihydropyridine calcium antagonist, in human plasma was developed. An internal standard, the deuterated analogue of racemic nilvadipine, was added to the plasma and extracted with an n-hexane:ethyl acetate (92.5:7.5) mixture under alkaline conditions. Each enantiomer in the extract was separated on a chiral stationary-phase column (Chiralpak OT(+)) for HPLC, and the effluents containing the respective isomers were collected. Each effluent was analyzed by fused-silica capillary column GC-electron capture negative ion chemical ionization MS. The mass spectrometer was set to monitor the molecular anions of nilvadipine and the internal standard. Calibration curves were linear for concentrations of each enantiomer from 0.025 to 10 ng/mL. The mean intra- and interassay precisions, as estimated by RSD, were less than 6% for each enantiomer. Assay suitability was assessed in a pharmacokinetic study in which four subjects were given a 6-mg oral dose of racemic nilvadipine. The t1/2 values of the two enantiomers were similar, but the AUC values of the more potent (+)-enantiomer were 2.4-3.6 times higher than those of its optical antipode.

Adult↗
PubMed2004

Determination of the purity of ampicillin by micellar electrokinetic chromatography and reversed phase liquid chromatography on a monolithic silica column.

A micellar electrokinetic chromatographic (MEKC) method and a fast reversed-phase liquid chromatographic one have been developed for determining the purity of ampicillin. MEKC separation of ampicillin and its related substances was performed with the use of an untreated fused-silica capillary and 40 mM phosphate-borate buffer, pH 7.5 containing 75 mM SDS. The HPLC method employed a monolithic silica C18 column and a mobile phase composed of phosphate buffer, pH 5.2 and ACN, the flow rate being 4.0 mL/min. Both methods were successfully validated. Linearity, relative response factors, limits of quantitation, intermediate precision, and accuracy were evaluated. The methods proved to be fast, reliable, and sufficiently sensitive and, accordingly, well-suited for control of purity of ampicillin substance, injections, and capsules. A combination of both methods can be very useful in the confirmation of impurity profiles.

Ampicillin↗
PubMed2005

Identification of impurities in acarbose by using an integrated liquid chromatography-nuclear magnetic resonance and liquid chromatography-mass spectrometry approach.

The usefulness of applying an integrated LC-NMR and LC-MS approach to acarbose bulk drug impurity profiling is demonstrated. LC-MS and LC-NMR methodologies were employed for the online separation and structural elucidation of a final drug product. Combining data provided by the stop-flow LC-NMR and LC-MS experiments made it possible to identify the main components present in the acarbose sample. Spectral analysis revealed that A and B were known impurities while C was an unknown compound. LC-MS and LC-NMR analyses revealed that C was a pentasaccharide differing from the acarbose in number and nature of sugar subunits in the molecule. It was subsequently isolated and its structure was confirmed by the offline 1- and 2-D NMR experiments, and atom assignment was made.

Acarbose↗
PubMed2005

Application of direct thermal desorption gas chromatography and comprehensive two-dimensional gas chromatography coupled to time of flight mass spectrometry for analysis of organic compounds in ambient aerosol particles.

Semivolatile organic compounds (SVOC) associated with ambient particles smaller than 2.5 microm (PM2.5) were determined in the city of Augsburg, Germany. Daily samples were collected at a central monitoring station from late summer 2002 to spring 2005. SVOC were analysed by direct thermal desorption (DTD)-GC and comprehensive 2-D GC coupled to TOF MS (DTD-GC-TOF MS and DTD-GC x GC-TOF MS). Two hundred compounds were quantified and 'semi-quantified' on a daily basis by DTD-GC-TOF MS. n-Alkanes, n-alkan-2-ones, n-alkanoic acid methyl esters, acetic acid esters, n-alkanoic acid amides, nitriles, linear alkylbenzenes and 2-alkyl-toluenes, hopanes, PAH, alkylated PAH and oxidised PAH, and several compounds that are not-grouped in homologous rows or compound classes were determined. Changes in concentration and pattern of several target compounds as well as methodological advantages and restrictions of DTD-GC-TOF MS are briefly discussed. DTD-GC-TOF MS analysis provided data particularly suited for source receptor modelling and epidemiological time series studies on the health effects of ambient PM. GC x GC enhances chromatographic resolution of PM samples and therefore amplifies the peak identification capabilities of the TOF MS.

Aerosols↗
PubMed1995

Separation of hemoglobin acetaldehyde adducts by high-performance liquid chromatography-cation-exchange chromatography.

A HPLC-based method was developed to provide a simple way to study changes to hemoglobin induced by acetaldehyde in vitro. This method distinguished 18 human hemoglobin fractions including a new acetaldehyde-induced fraction HbA1ach3. The method consists of a Poly CAT A cation-exchange column and a stepwise salt and pH gradient, with a total analysis time of 31 min. The formation of acetaldehyde adducts was studied by incubation of hemoglobin with different Ach concentrations (5-1000 microM) and different incubation times (0-48 h). Physiological (5-250 microM) Ach concentrations induced increases mainly in 3 known fractions: HbA1ach1, HbA1prec, and HbA1d3; plus, it caused the formation of a new fraction, HbA1ach3. The specificity of the changes to acetaldehyde was studied by incubation of hemoglobin with glucose and acetylsalicylic acid. HbA1ach3 was the only acetaldehyde-induced hemoglobin fraction which was not also increased by glucose and acetylsalicylic acid treatment. The formation of HbA1ach3 showed a dose and time dependence on acetaldehyde incubations. Dialyzation and reduction experiments showed that HbA1ach3 is a stable adduct of hemoglobin, and incubation with purified HbAO showed that HbA1ach3 is an adduct of HbAO. The within-run and between-run coefficients of variation for HbA1ach3 (0.83% of total hemoglobin) were 10.8 and 15.1%, respectively, and the analytical recovery was 82-97%. These results indicate that in addition to the new, acetaldehyde-specific fraction HbA1ach3, several other types of hemoglobin adducts were formed with acetaldehyde. The current method might be useful in clarifying the relationships between hemoglobin and acetaldehyde in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaldehyde↗
PubMed1999

Investigations of S-transnitrosylation reactions between low- and high-molecular-weight S-nitroso compounds and their thiols by high-performance liquid chromatography and gas chromatography-mass spectrometry.

S-Transnitrosylation reactions are supposed to be the basic principle by which nitric oxide-related biological activities are regulated in vivo. Mechanisms of S-transnitrosylation reactions are poorly understood and equilibria constants for physiological S-nitroso compounds and thiols are rare. In the present study we investigated S-transnitrosylation reactions of the thiols homocysteine, cysteine, glutathione, N-acetylcysteine, N-acetylpenicillamine, and human plasma albumin and their corresponding S-nitroso compounds SNhC, SNC, GSNO, SNAC, SNAP, and SNALB utilizing high-performance liquid chromatographic and gas chromatographic-mass spectrometric techniques. These methods allowed to study S-transnitrosylation reactions in mixtures of several S-nitroso compound/thiol pairs, to determine equilibria constants, and to elucidate the mechanism of S-transnitrosylation reactions. We obtained the following order for the equilibria constants in aqueous buffered solution at pH 7.4: SNhC approximately SNAC > GSNO approximately SNALB > SNAP > SNC. Our results suggest that the mechanism of S-transnitrosylation reactions of these S-nitroso compounds and their thiols involve heterolytic cleavage of the S&sbond;N bond. Incubation of SNC with human red blood cells resulted in a dose-dependent formation of GSNO in the cytosol through S-transnitrosylation of intracellular GSH by the SNC transported into the cells. This reaction was accompanied with an almost complete disappearance of the SNC fraction transported into the cells. This finding is in full agreement with the equilibrium constant Keq of 1.9 for the reaction SNC + GSH <--> Cys + GSNO in aqueous buffer.

Acetylcysteine↗