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At least 1,027 records · Page 57Linked to original sources
PubMed1980

Reversed- and normal-phase high-performance liquid chromatography of 18-hydroxylated steroids and their derivatives. Comparison of selectivity, efficiency and recovery from biological samples.

The chromatographic behaviour of adrenal 18-hydroxysteroids, and a series of derivatives thereof, has been studied in reversed-phase and normal-phase high-performance liquid chromatography (HPLC). Both 18-hydroxycorticosterone and 18-hydroxy-11-deoxycorticosterone exhibited a marked loss of chromatographic efficiency when separated on incompletely-covered C18 reversed-phase supports (as determined by methyl red adsorption) showed no such effect, nor was it seen when aprotic solvents, such as dioxane, were used. This phenomenon is unique among the wide range of adrenal and testicular steroids that we have studied and affords a useful test, applicable under aqueous conditions, of coverage by the alkylsilane reversed phase, a factor of considerable importance in the successful resolution of complex mixtures of adrenal steroids by reversed-phase HPLC. The retention times of the 20-methoxy, 20-ethoxy, 21-acetoxy, etiolactone, 11 beta, 18-ether and dimeric derivatives of the naturally-occurring 18-hydroxysteroids have been determined in relation to major adrenal steroids. Procedures for extraction and reversed-phase HPLC of 18-hydroxysteroids from tissues without the formation of these less polar forms, which can complicate their separation by other chromatographic techniques, are illustrated with respect to a human malignant adrenocortical tumour which caused hypermineralocorticism.

Chemical Phenomena↗
PubMed1982

Determination of apovincaminic acid in biological samples by high-performance liquid chromatography.

A method is described for measuring the concentrations of apovincaminic acid and vincaminic acid (internal standard) in blood plasma and urine by high-performance liquid chromatography using ion pair extraction. The main metabolite of vinpocetine, apovincaminic acid, and vincaminic acid were extracted from 1 ml of plasma and urine into chloroform as an ion pair using tetrabutylammonium hydroxide as counter ion. Analysis was carried out on a reversed-phase column of RP-8 with acetonitrile-0.0075 M phosphate buffer (28:72) at pH 3.5 as mobile phase. The eluted derivatives were detected by UV absorption at 254 nm. The sensitivity of the method is 20 ng/ml for AVA in plasma and urine samples. The relative recovery of these compounds added to plasma was about 50%.

Chromatography, High Pressure Liquid↗
PubMed1981

Determination of opiates in biological samples by glass capillary gas chromatography with electron-capture detection.

A gas chromatographic method for the simultaneous determination of morphine, 6-acetylmorphine and codeine in human plasma or blood has been developed. The samples are buffered to pH 9 and extracted on silica columns, cleaned by extraction and finally acylated with pentafluoropropionic anhydride. The derivatives formed are separated on a glass capillary column with falling glass needle injection and electron-capture detection. The choice of the extraction conditions and the preparation of suitable capillary columns are discussed.

Chromatography, Gas↗
PubMed1982

Gas chromatographic determination of deltamethrin in biological samples.

A gas chromatographic method is described for the detection and estimation of deltamethrin in spiked samples of urine, feces, milk, liver, kidney, muscle and subcutaneous fat. It involved extraction with acetone, with the exception of milk and urine samples, liquid-liquid partition with acetonitrile, followed by clean-up on a micro-column using benzene-hexane (1:1) solvent system. Milk and urine samples were extracted with hexane followed by liquid-liquid partition with acetonitrile. Under the gas chromatographic conditions employed, deltamethrin eluted in less than 4 min.

Adipose Tissue↗
PubMed1981

Fluorescence labelling in trace analysis of biological samples: simultaneous determination of free fatty acids and related carboxylic compounds.

Free fatty acids in serum, together with representatives of a new class of oxirane carboxylic acids having blood-glucose-lowering activity, were determined simultaneously by fluorescence labelling with 4-bromomethyl-7-methoxycoumarin (Br-Mmc) followed by separation by high performance liquid chromatography. Esterification kinetics of selected compounds were studied, and separation conditions for analysis of oxirane carboxylic acids, related compounds, and a series of saturated and unsaturated fatty acids as their Mmc estes were established. Three compounds (3, 6 and 7) were determined from serum quantitatively by extraction, derivatization, and analysis by high-performance liquid chromatography. Detection limits from serum (1ml) were 50 ng/ml. Two hours after intravenous bolus injection of 10 mg/kg of compound 6 in dog, a serum level of 1.1 mg/1 of administered compound was determined.

Animals↗
PubMed1986

Analysis of organophosphorus insecticides in biological samples by selective ion monitoring gas chromatography-mass spectrometry.

Gas chromatography with chemical ionization or electron impact mass spectrometry and selected ion monitoring provided a simple and sensitive method for measuring organophosphorus insecticides. Chemical ionization produced higher-mass ions which might increase the selectivity and sensitivity of the assay. The recovery of organophosphates from saline and urine was greater than 75%. The recovery of these compounds from plasma was less than the saline because of the binding of insecticides to plasma protein. Insecticides with lower LD50 values showed lower recovery from plasma than organophosphates with higher LD50 values.

Gas Chromatography-Mass Spectrometry↗
PubMed2001

Dialysis-solid-phase extraction combined on-line with non-aqueous capillary electrophoresis for improved detectability of tricyclic antidepressants in biological samples.

Dialysis-solid-phase extraction (SPE) sample pretreatment is combined on-line with non-aqueous capillary electrophoresis for the determination of tricyclic antidepressants in urine and serum. After clean-up and enrichment, the water is removed from the sample matrix and the analytes are eluted from the cartridge by means of an organic solvent. Next, the eluate is transported to the capillary and the injection is performed electrokinetically. This injection, which does not suffer from an adverse sample matrix effect because of the SPE step, results in further analyte concentration. The detection limits are in the 0.02-0.1 microg/ml range and the day-to-day repeatabilities are between 2.5 and 9.5%, which is quite satisfactory.

Antidepressive Agents, Tricyclic↗
PubMed2001

Determination of actinides in environmental and biological samples using high-performance chelation ion chromatography coupled to sector-field inductively coupled plasma mass spectrometry.

High-performance chelation ion chromatography, using a neutral polystyrene substrate dynamically loaded with 0.1 mM dipicolinic acid, coupled with sector-field inductively coupled plasma mass spectrometry has been successfully used for the separation of the actinides thorium, uranium, americium, neptunium and plutonium. Using this column it was possible to separate the various actinides from each other and from a complex sample matrix. In particular, it was possible to separate plutonium and uranium to facilitate the detection of the former free of spectral interference. The column also exhibited some selectivity for different oxidation states of Np, Pu and U. Two oxidation states each for plutonium and neptunium were found, tentatively identified as Np(V) and Pu(III) eluting at the solvent front, and Np(IV) and Pu(IV) eluting much later. Detection limits were 12, 8, and 4 fg for 237Np, 239Pu, and 241Am, respectively, for a 0.5 ml injection. The system was successfully used for the determination of 239Pu in NIST 4251 Human Lung and 4353 Rocky Flats Soil, with results of 570+/-29 and 2939+/-226 fg g(-1), respectively, compared with a certified range of 227-951 fg g(-1) for the former and a value of 3307+/-248 fg g(-1) for the latter.

Actinoid Series Elements↗
PubMed1988

Direct enantiomeric separation of betaxolol with applications to analysis of bulk drug and biological samples.

A direct method is described for the resolution of the enantiomers of betaxolol, a novel cardioselective beta-adrenergic blocking agent, using a tris(3,5-dimethylphenylcarbamate)cellulose chiral column. An excellent resolution of the two antipodes is obtained (Rs greater than 2) with high peak symmetries. The method is simple and ideally suited to the routine control of the enantiomeric excess in the bulk drug and the analysis of the enantiomers of betaxolol in hepatocyte suspensions. With modification of the polar modifier in a hexane-based mobile phase, most commercially available beta-blockers can be baseline resolved.

Adrenergic beta-Antagonists↗
PubMed1988

Quantitation of free amino acids in biological samples by high-performance liquid chromatography. Application of the method in evaluating amino acid levels in cerebrospinal fluid and plasma of patients with multiple sclerosis.

An automatic on-line high-performance liquid chromatographic method based on a precolumn derivatization with o-phthalaldehyde has been developed to quantitate levels of free amino acids in cerebrospinal fluid (CSF) and plasma samples from 12 patients with multiple sclerosis (MS) and 12 controls. The analytical method gave reproducible results with relative standard deviations of 0.5-3% for all amino acids. The separation of 24 amino acids was performed on a reversed-phase C18 column, using two solvents and a multiple-step gradient. Each chromatographic experiment was completed within 40 min. The results showed higher levels of Glu, Gln, Gly and Ala and lower levels of Met, Val, Phe and Lys in plasma of MS patients. In CSF, increased levels of Gln, Arg, Ser and Tyr and decreased levels of Asp, Glu, Met, gamma-aminobutyric acid and Phe were found in MS patients, whereas the levels of other amino acids remained more or the less same in both groups.

Amino Acids↗
PubMed1988

High-performance liquid chromatographic evaluation of salicyloyl pyridixol and systemic metabolites in biological samples.

An high-performance liquid chromatographic analytical method, which allows quantitative evaluation of both salicyloyl pyridixol and its metabolite salicylic acid, is reported. This method has demonstrated to possess the required specifications in terms of linearity, sensitivity, extraction recovery, reproducibility and specificity for pharmacokinetic investigations in both human subjects and experimental animals. The results obtained from an investigation on the rat are briefly discussed.

Animals↗