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At least 1,171 records · Page 65Linked to original sources
PubMed2002

Simultaneous determination of hypericin and hyperforin in human plasma and serum using liquid-liquid extraction, high-performance liquid chromatography and liquid chromatography-tandem mass spectrometry.

A method for the simultaneous extraction of hypericin and hyperforin from a St. John's Wort extract, which is used in case of moderate depressions and skin injuries, from human plasma and serum by liquid-liquid extraction (LLE) with n-hexane-ethylacetate (70:30, w/w) was developed. A reversed-phase high-performance liquid chromatographic (RP-HPLC) method with UV, fluorescence (FLD) and mass spectrometric (MS) detection using electrospray ionization (ESI) was used to identify and quantify hypericin and hyperforin in the extracts from blood samples. Linearity was obtained in the ranges 8.4-28.7 ng/ml (hypericin) and 21.6-242.6 ng/ml (hyperforin). Recoveries were between 32.2 and 35.6% for hypericin and 100.1 and 89.9% for hyperforin. Intra-day accuracy and precision for this method ranged between 3.2 and 4.3% and 2.6 and 2.8%, respectively. After validation of the LLE, the method was tested on real plasma samples which were obtained by ingestion of St. John's Wort extract capsules. Blood samples were taken 2, 4, and 6 h after ingestion. Finally, this method proved to be highly suitable for clinical and pharmacologically relevant studies.

Anthracenes↗
PubMed2003

Determination of 13C and 15N enrichments of urea in plasma by gas chromatography-combustion isotope ratio mass spectrometry and gas chromatography-mass spectrometry using the 2-methoxypyrimidine derivative.

We describe a GC-MS and GC-c-IRMS method for the determination of labeled urea tracer enrichments in plasma as a result of combined 13C- and 15N(2)-urea infusion experiments in piglets. Urea was converted into 2-methoxypyrimidine, a stable derivative, suited for analyses by both GC-MS and GC-c-IRMS. Using calibration curves for the respective working ranges (13C-urea: 0-1% APE; 15N(2)-urea: 0-7% MPE) enrichments were established in single point measurements; for 15N(2)-urea as values+/-0.15% MPE (95% confidence interval); for 13C-urea as values+/-0.02% APE (95% confidence interval). 15N(1)-urea enrichments were determined by measurement of the same sample with GC-c-IRMS and GC-MS. Subtraction of the 13C specific GC-c-IRMS data from the nondiscriminating GC-MS data for the sum of 13C- and 15N(1)-urea resulted in 15N(1)-urea enrichments+/-0.15% MPE (95% confidence interval). Application of the method in a combined 13C-urea bolus and 15N(2)-urea primed constant infusion experiment in piglet was demonstrated.

Animals↗
PubMed1998

Rapid preconcentration method for the determination of pyrethroid insecticides in vegetable oils and butter fat and simultaneous determination by gas chromatography-electron capture detection and gas chromatography-mass spectrometry.

A simple and rapid solid-phase extraction (SPE)-GC method for the preconcentration and quantification of pyrethroids at low nanogram levels in oils and high fat content samples is presented. The method was studied using seven highly persistent pyrethroid insecticides, viz., cypermethrin, deltamethrin, fenvalerate, cyfluthrin, allethrin, cyhalothrin and permethrin. Preconcentration was achieved by treating the oil samples with methyltrioctylammonium chloride and subsequent elution of the pyrethroid molecules from a graphitized carbon black SPE cartridge using 5 ml of acetonitrile. Pyrethroid quantification was achieved by GC with electron capture detection. Recoveries of the pyrethroids at fortification levels of 0.05-0.5 ppm were 94-105%. Storage on graphitized carbon black for 30 d lowered the recovery of the pyrethroids by only 3-6%. The method compared well with results obtained by a GC-MS method. The relative standard deviation at a concentration level of 0.05-0.2 microgram ml-1 ranged from 1.31 to 5.16%. The limit of detection achieved was 0.002 microgram ml-1 without any additional clean-up and with little interference from lipids during analysis.

Animals↗
PubMed1996

Analysis of protein-bound metabolites of furazolidone and furaltadone in pig liver by high-performance liquid chromatography and liquid chromatography-mass spectrometry.

Studies undertaken using radiolabelled furazolidone have demonstrated the covalent binding of residues of the drug to cellular protein in vivo. A portion of these bound residues and those formed by furaltadone, a related nitrofuran drug, possess intact side-chains, 3-amino-2-oxazolidinone (AOZ) and 5-morpholino-methyl-3-amino-2-oxazolidinone (AMOZ), respectively. These side-chains have molecular characteristics in common with the parent compounds and may be released from liver tissue under mild acidic conditions. Derivatization with 2-nitrobenzaldehyde (NBA) serves to isolate the released side-chains and the derivatives NPAOZ and NPAMOZ are chromophoric, thereby permitting UV detection. This paper reports the introduction of an extract clean-up step to the existing procedure which eliminates or decreases interference from NBA in the HPLC-UV determination of NPAOZ. The modified procedure was also applied to the determination of AMOZ. The development of an LC-MS method for the quantitative and confirmatory determination of AOZ and AMOZ extracted and derivatized according to the same procedure as that for HPLC-UV is described. The methods were validated for AOZ and AMOZ in fortified (intra- and inter-assay studies) and incurred (inter-assay studies) pig liver samples. The limit of determination for fortified control liver samples was 5 ng AOZ g-1 and 10 ng AMOZ g-1 by HPLC-UV and 10 ng AOZ or AMOZ g-1 by LC-MS. In addition, a study to determine the ratio of released AOZ to the total bound residues present in incurred liver samples from pigs treated with furazolidone is described.

Animals↗
PubMed1981

Affinity chromatography of yeast alpha-glucosidase using ligand-mediated chromatography on immobilized phenylboronic acids.

The synthesis of 3-nitro-4-(6-aminohexylamido)phenylboronic acid is described. The properties of two novel forms of immobilized phenylboronate agarose adsorbents [m-aminophenylboronic acid-Matrex Gel and 3-nitro-4-(6-aminohexylamido)phenylboronic acid-Sepharose CL-6B] were investigated. Both gels bind and selectively retard the glycoprotein alpha-glucosidase from yeast. The retardation is affected by following parameters: (i) pH, (ii) presence of sugar, (iii) concentration of sugar and (iv) buffer species (especially triethanolamine). Five sugars were studied, namely sorbitol, fructose, ribose, glucose and maltose. The concentration of sugar required to produce significant retardation increased in the above order, whereas the ability of sugar to form a complex with boron decreases in the same order. These effects were observed with crude as well as pure enzyme. Since alpha-glucosidase is a glycoprotein, it is proposed that this protein is mainly bound to these immobilized phenylboronates via sugar (glyco) residues. Displacement of the enzyme from the column is effected by the sugar in the buffer (or in a preincubation mixture). However, the marked pH-dependence (this retardation effect could only be observed at pH 7.4) suggests that these results are not due solely to hydrophobic or ionic mechanisms and are more complex than simple sugar-phenylboronic acid interactions.

Boronic Acids↗
PubMed2001

Direct thermal desorption in the analysis of cheese volatiles by gas chromatography and gas chromatography-mass spectrometry: comparison with simultaneous distillation-extraction and dynamic headspace.

Direct thermal desorption (DTD) has been used as a technique for extracting volatile components of cheese as a preliminary step to their gas chromatographic (GC) analysis. In this study, it is applied to different cheese varieties: Camembert, blue, Chaumes, and La Serena. Volatiles are also extracted using other techniques such as simultaneous distillation-extraction and dynamic headspace. Separation and identification of the cheese components are carried out by GC-mass spectrometry. Approximately 100 compounds are detected in the examined cheeses. The described results show that DTD is fast, simple, and easy to automate; requires only a small amount of sample (approximately 50 mg); and affords quantitative information about the main groups of compounds present in cheeses.

Cheese↗
PubMed1990

Measurement of vancomycin in renally impaired patient samples using a new high-performance liquid chromatography method with vitamin B12 internal standard: comparison of high-performance liquid chromatography, emit, and fluorescence polarization immunoassay methods.

A new reverse-phase high-performance liquid chromatographic (HPLC) procedure has been developed for the quantitation of vancomycin and its crystalline degradation product, CDP-1. The new HPLC procedure involves a liquid-liquid extraction pretreatment procedure and an HPLC internal standard, vitamin B12. The new HPLC procedure was used to measure 50 renally impaired patient samples. Samples were than analyzed by the monoclonal antibody Emit vancomycin assay, and the polyclonal antibody fluorescence polarization immunoassay (FPIA) vancomycin assay, and the results were compared. The Emit vancomycin assay correlated well with HPLC, but FPIA quantitated higher than Emit and HPLC. We conclude that the polyclonal antibody FPIA assay detects CDP-1 in the samples of renally impaired patients, accounting for an average of 10% of the FPIA/Emit bias, and should therefore be used with caution when monitoring vancomycin levels in renally impaired patients.

Chromatography, High Pressure Liquid↗