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At least 343 records · Page 19Linked to original sources
PubMed2003

Comparison of reversed-phase liquid chromatography and hydrophilic interaction/cation-exchange chromatography for the separation of amphipathic alpha-helical peptides with L- and D-amino acid substitutions in the hydrophilic face.

Mixed-mode hydrophilic interaction/cation-exchange chromatography (HILIC/CEX) is a novel high-performance technique which has excellent potential for peptide separations. Separations by HILIX/CEX are carried out by subjecting peptides to linear increasing salt gradients in the presence of high levels of acetonitrile, which promotes hydrophilic interactions overlaid on ionic interactions with the cation-exchange matrix. In the present study, HILIC/CEX has been compared to reversed-phase liquid chromatography (RP-HPLC) for separation of mixtures of diastereomeric amphipathic alpha-helical peptide analogues, where L- and D-amino acid substitutions were made in the centre of the hydrophilic face of the amphipathic alpha-helix. Unlike RP-HPLC, temperature had a substantial effect on HILIC/CEX of the peptides, with a rise in temperature from 25 to 65 degrees C increasing the retention times of the peptides as well as improving resolution. Our results again highlight the potential of HILIC/CEX as a peptide separation mode in its own right as well as an excellent complement to RP-HPLC.

Amino Acid Substitution↗
PubMed2003

Dextrin characterization by high-performance anion-exchange chromatography--pulsed amperometric detection and size-exclusion chromatography--multi-angle light scattering--refractive index detection.

Starch hydrolysis products, or dextrins, are widely used throughout the food industry for their functional properties. Dextrins are saccharide polymers linked primarily by alpha-(1 --> 4) D-glucose units and are prepared by partial hydrolysis of starch. Hydrolysis can be accomplished by the use of acid, enzymes, or by a combination of both. The hydrolysis products are typically characterized by the "dextrose equivalent" (DE), which refers to the total reducing power of all sugars present relative to glucose. While the DE gives the supplier and buyer a rough guide to the bulk properties of the material, the physiochemical properties of dextrins are dependent on the overall oligosaccharide profile. High-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detection and size-exclusion chromatography (SEC) with multi-angle light-scattering and refractive index detection were used to characterize dextrins from commercial sources. HPAEC was used to acquire the oligosaccharide profile, and SEC to obtain an overall molar mass distribution. These methods in combination extended our understanding of the relationship between oligosaccharide profile, DE, and the hydrolysis process. Data from the two techniques enabled a method for estimating the DE that gave results in reasonable agreement with the accepted titration method.

Anions↗
PubMed1998

Immunoaffinity chromatography combined on-line with high-performance liquid chromatography-mass spectrometry for the determination of corticosteroids.

On-line coupled immunoaffinity chromatography-reversed-phase high-performance liquid chromatography (IAC-HPLC) with detection by quadrupole ion trap mass spectrometry using a particle beam interface has been developed for the determination of the steroids, dexamethasone and flumethasone. HEMA (polyhydroxyethylmethacrylate) was evaluated as a support material for the anti-dexamethasone antibodies used in IAC. Antibody cross-reactivity and non-specific binding have been investigated for the HEMA bound anti-dexamethasone IAC column. The on-line IAC-HPLC-MS determination of dexamethasone and flumethasone in post-administration equine urine samples showed precisions (R.S.D.) of 8.0 and 7.1%, respectively, with limits of detection in the range 3-4 ng/ml.

Adrenal Cortex Hormones↗
PubMed1998

Determination of a variety of chemical classes of pesticides in surface and ground waters by off-line solid-phase extraction, gas chromatography with electron-capture and nitrogen-phosphorus detection, and high-performance liquid chromatography with post-column derivatization and fluorescence detection.

Octadecyl (C18)-bonded porous silica was evaluated for the extraction of triazines, organochlorine, carbamates and acidic pesticides from surface and ground water. Gas chromatography with selected detection methods (electron-capture detection, nitrogen-phosphorus detection, mass spectrometry) and liquid chromatography-post-column derivatization fluorescence detection was employed for the determination of 32 pesticides. Recoveries varied from 52 to 102%. The recoveries of triazines obtained using C18 extraction cartridges and conventional liquid-liquid extraction (LLE) are compared. The limit of detection for seventeen organochlorine compounds was better than 0.003 microgram/l and the limit of detection for other 15 analytes was better than 0.06 microgram/l. The proposed analytical methodology was applied to analyze pesticides in surface and ground-water samples of the Lassithi Plateau, Crete, Greece.

Chromatography, Gas↗
PubMed1998

Determination of organonitrogen pesticides in large volumes of surface water by liquid-liquid and solid-phase extraction using gas chromatography with nitrogen-phosphorus detection and liquid chromatography with atmospheric pressure chemical ionization mass spectrometry.

During a recent study to determine the fluxes and fates of contaminants in the St. Lawrence River, the majority of organonitrogen pesticides analysed in samples of surface water were found in the dissolved phase. This paper compares two extraction techniques and two analytical techniques for 10 chemicals (metolachlor, seven triazines and two degradation products of atrazine-cyanazine-propazine and simazine) in the dissolved phase in large volumes of surface water, using a fibre glass filter with 0.7 micron porosity. Samples of filtered surface water (1-20 l) were extracted by means of a liquid-liquid technique using the Goulden large-sample extractor, and by means of a solid-phase extraction technique, using cartridges filled with 500 mg of a large particle-size graphitized carbon black as adsorbent: Carbopack B (500-666 microns). The pesticides were analysed by gas chromatography on two DB-5 and DB-210 capillary columns with nitrogen-phosphorus detection (GC-NPD) and by liquid chromatography coupled with mass spectrometry equipped with an atmospheric pressure chemical ionization interface (LC-APCI-MS). The recoveries were high (67-100%) for the majority of the target pesticides in a volume of 17.85 l of Milli-Q water, compared to recoveries in the same volume of filtered surface water (51-102%). The detection limits ranged from 0.4 to 4 ng/l and from 0.6 to 3 ng/l for GC-NPD and LC-ACPI-MS techniques, respectively.

Chromatography, Gas↗
PubMed1999

Application of gas chromatography-cryocondensation-Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry to the identification of gas phase reaction products from the alpha-pinene/ozone reaction.

The gas phase reaction of alpha-pinene with the atmospheric oxidant ozone was investigated by using the capabilities of both gas chromatography-cryocondensation-Fourier transform infrared spectroscopy (GC-FT-IR) and gas chromatography-mass spectrometry (GC-MS), for the identification of the reaction products formed. The reaction was carried out in a flow reaction chamber from where the compounds were sampled on Tenax-containing adsorption cartridges. The reaction mixture was injected onto the column after thermodesorption and analyzed using both GC-IR and GC-MS. Twenty compounds could be detected, including the reactant alpha-pinene and it's impurities tricyclene and camphene. Eleven compounds were identified by spectra comparison with either reference data or spectra obtained from commercial standards. Four compounds were tentatively identified from their IR and MS spectra, while from the remaining two compounds the nature of basic functional groups could be established.

Bicyclic Monoterpenes↗
PubMed2000

Comparative methodology in the determination of alpha-oxocarboxylates in aqueous solution ion chromatography versus gas chromatography after oximation, extraction and esterification.

The alpha-oxocarboxylates (alpha-ketocarboxylates) and the corresponding alpha-oxoacids (alpha-ketoacids) have been reported as byproducts of ozonation of potable water supplies. Some of these species also occur in biophysiological systems. Five analytes were investigated in this study: oxoethanoate (glyoxylate), 2-oxopropanoate (pyruvate), 2-oxobutanoate (2-ketobutyrate), 2-oxopentanoate (2-ketovalerate) and oxopropanedioate (ketomalonate, mesoxalate). Ion chromatography (IC) and gas chromatography (GC) were evaluated for the quantitation of these analytes at concentrations < or =200 ng ml(-1). For the IC method, the samples are run directly with minimal to no pre-treatment. For the GC method, the analytes must be derivatized with O-(2,3,4,5,6-pentafluorobenzyl)oxylamine to form oximes. The oximes are extracted into tert-butyl methyl ether and the carboxylic acid is esterified (methylated) with diazomethane. It was concluded that the ion chromatographic determination is significantly superior to the gas chromatographic method for these analytes.

Carboxylic Acids↗
PubMed2000

Development of a simple in-vial liquid-phase microextraction device for drug analysis compatible with capillary gas chromatography, capillary electrophoresis and high-performance liquid chromatography.

A simple, inexpensive and disposable device for liquid-phase microextraction (LPME) is presented for use in combination with capillary gas chromatography (GC), capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC). 1-4 ml samples of human urine or plasma were filled into conventional 4-ml vials, whereafter 15-25 microl of the extraction medium (acceptor solution) was filled into a short piece of a porous hollow fiber and placed into the sample vial. The drugs of interest were extracted from the sample solutions and into the small volumes of acceptor solution based on high partition coefficients and were preconcentrated by a factor of 30-125. For LPME in combination with GC, the porous hollow fiber was filled with 15 microl n-octanol as the acceptor solution. Following 30 min of extraction, the organic acceptor solution was injected directly into the GC system. For LPME in combination with CE and HPLC, n-octanol was immobilized within the pores of the hollow fiber, while the internal volume of the fiber was filled with either 25 microl of 0.1 M HCl (for extraction of basic compounds) or 25 microl 0.02 M NaOH (for acidic compounds). Following 45 min extraction, the aqueous acceptor solution was injected directly into the CE or HPLC system. Owing to the low cost, the extraction devices were disposed after a single extraction which eliminated the possibility of carry over effects. In addition, because no expensive instrumentation was required for LPME, 10-30 samples were extracted in parallel to provide a high number of samples per unit time capacity.

Blood Chemical Analysis↗
PubMed1993

High-performance liquid chromatography of amino acids, peptides and proteins. CXXX. Modified porous zirconia as sorbents in affinity chromatography.

The utilisation of organosilanes to introduce active chemical groups onto zirconia surfaces, suitable for the subsequent immobilisation of proteins or other biomimetic ligands, is described. Two different types of porous zirconia-based particles with nominal pore diameters of 160 and 1000 A pore size were modified with two different affinity ligands. In the first case, methods to immobilise iminodiacetic acid-Cu(II) and its application in Cu(II) immobilised metal ion affinity chromatography (IMAC) were established. In the second series of experiments, concanavalin A was immobilised and the interaction of this lectin with the enzyme horseradish peroxidase examined. For both systems, adsorption isotherms were recorded as batch experiments. In each case, the experimental results could be fitted to langmuirean type adsorption isotherms, indicating that under the chosen conditions only one type of interaction is present, with nonspecific interactions with the support surface playing an insignificant role. These studies document the potential of surface modified zirconia particles for the immobilisation of chemical ligands or proteins for use in biospecific affinity chromatography and immobilised enzyme bioreactors.

Adsorption↗
PubMed1976

Determination of 15-keto-13,14-dihydro-metabolites of PGE2 and PGF2alpha in plasma using high performance liquid chromatography and gas chromatography-mass spectrometry.

A method is described for the measurement of 15-keto-13,14-dihydrometabolites of PGE2 and PGF2alpha in peripheral human plasma. This involves purification by high performance liquid chromatography followed by determination of levels by combined gas chromatography-mass spectrometry using tetradeuterated analogs of the metabolites as internal standards. The levels of these metabolites in plasma are considered to be a more reasonable index of the entry of PGE2 and PGF2alpha into peripheral blood than are the levels of the corresponding primary prostaglandins. The endogenous levels of 15-keto-13, 14-dihydro-PGE2 and 15-keto-13,14-dihydro-PGF2alpha found in peripheral plasma are 33 +/- 10 pg/ml (SD; n=6) and 40 +/- 16 pg/ml (SD; n=6), respectively.

Chromatography, Gas↗
PubMed2000

Methods for the determination of seven selective serotonin reuptake inhibitors and three active metabolites in human serum using high-performance liquid chromatography and gas chromatography.

This paper describes a set of simple and sensitive multiresidue methods for the determination of the specific serotonin reuptake inhibitors (SSRIs) used as antidepressant drugs, and some of their respective active metabolites in human serum. It involves liquid-liquid extraction procedures followed by gas chromatography coupled to nitrogen phosphorus detection or isocratic reversed-phase high-performance liquid chromatography combined with fluorescence detection (HPLC-FL), depending on the analytes. Extraction recoveries were between 71 and 96% for the eight SSRIs and their metabolites analysed by GC and between 41 and 77% for the two of them analysed by HPLC. Limits of detection (LODs) and limits of quantitation (LOQs) ranged, respectively, from 2.5 to 5 microg/l and from 10 to 20 microg/l. Intra-assay and inter-assay precision was studied at three and four concentration levels, respectively, and was less than 19% for all compounds. Accuracy was also satisfactory for all. An excellent linearity was observed from the LOQs up to 1000 microg/l for milnacipram and paroxetine and from each LOQ up to 400 mg/l for the other compounds. The performance of the methods described thus allows the therapeutic drug monitoring of the currently commercialised SSRIs.

Antidepressive Agents, Second-Generation↗
PubMed2000

Determination of nitrate in blood by gas chromatography and gas chromatography-mass spectrometry.

We devised a sensitive and simple method for determining nitrate in whole blood, using an extractive alkylation technique. Nitrate in whole blood was reduced to nitrite by hydrazine sulfate in the presence of Cu2+ and Zn2+ as catalysts, and alkylated with pentafluorobenzyl bromide using tetradecyldimethylbenzylammonium chloride as the phase-transfer catalyst. The obtained derivative was analyzed qualitatively by gas chromatography-mass spectrometry and quantitatively by gas chromatography with electron-capture detection. The detection limit of nitrate in whole blood was 0.01 mM. The calibration curve was linear over the concentration range from 0.02 to 1.0 mM for nitrate in whole blood. The accuracy and precision of the method were evaluated and the relative standard deviations were found to be within 10%. Using this method, the blood nitrate levels of two victims who committed suicide by inhaling automobile exhaust gas were determined.

Alkylation↗
PubMed2000

Precise analysis of primary amino acids in urine by an automated high-performance liquid chromatography method: comparison with ion-exchange chromatography.

A precise, simple and rapid method for the quantitative determination of primary amino acids in urine based on high-performance liquid chromatography and o-phthaldialdehyde pre-column derivatization is described. All primary urinary amino acids could be determined within 49 min (injection to injection). Amino acid concentrations in 40 urinary samples were measured by this method and the results were compared with those measured by ion-exchange chromatography. The correlation coefficient for the common amino acids was greater than 0.90. This is the first study in which such a detailed comparison has been made on urine samples. It appeared that the method described is an excellent alternative to the classical ion-exchange method for the quantitation of urinary amino acids.

Adolescent↗
PubMed2001

Analysis of cocaethylene, benzoylecgonine and cocaine in human urine by high-performance thin-layer chromatography with ultraviolet detection: a comparison with high-performance liquid chromatography.

Cocaine and ethanol are frequently used at the same time, resulting in the formation of cocaethylene by transesterification. We studied the capability of high-performance thin-layer chromatography (HPTLC) to simultaneously detect cocaethylene, cocaine and benzoylecgonine in 16 urine specimens of drug addicts, previously tested as positive for benzoylecgonine at immunoenzymatic screening. Accuracy and precision, as well as detection and quantitation limits of the method, were evaluated by comparison with high-performance liquid chromatography (HPLC). HPTLC limit of quantitation was 1.0 microg/ml for the three compounds, whereas HPLC limits were 0.2 microg/ml for benzoylecgonine and cocaine, and 0.1 microg/ml for cocaethylene. The relative standard deviation (RSD) ranged from 1.03 to 12.60% and from 1.56 to 16.6% for intra- and inter-day HPTLC analysis, respectively. In the case of the HPLC method, the RSD for the intra-day precision ranged from 0.79 to 5.05%, whereas it ranged from 1.19 to 10.64% for the inter-day precision. In comparison with HPLC, HPTLC is less expensive and faster, requiring 2-3 h to analyze 10-12 samples on a single plate. In conclusion, HPTLC is suitable for determinations of the three analytes only for samples with high concentrations.

Chromatography, High Pressure Liquid↗
PubMed2001

Application of a new analytical method using gas chromatography and gas chromatography-mass spectrometry for the azide ion to human blood and urine samples of an actual case.

We have established a practical and reliable method to identify and quantify the azide ion in human whole blood and human urine by transforming the ion into pentafluorobenzyl azide (PFBN3). PFBN3 was simply derived from a reaction of the ion with an excess amount of pentafluorobenzyl bromide (PFBBr). The excess amount of PFBBr was removed from the products by its reaction with sodium thiosulfate. PFBN3 in the sample was detected in high sensitivity by gas chromatography with nitrogen-phosphorus detector (GC-NPD) and gas chromatography-mass spectrometry (GC-MS). The lower detection limits of the ion by GC-NPD were 5 ng/ml for human whole blood sample and 0.5 ng/ml for human urine sample at S/N=3. On the other hand, they were 100 ng/ml for human whole blood sample and 10 ng/ml for human urine sample by the full-scan mode of GC-MS. The analytical method was applied to identification and quantification of the ion in the actual whole blood and urine samples of the victims in an actual criminal case.

Azides↗
PubMed1981

Determination of antrafenine and its main acid metabolite, 2-{[7-(trifluoromethyl)-4-quinolinyl]amino}-benzoic acid, in biological fluids using high-performance liquid chromatography with large volume automatic injection and gas-liquid chromatography with derivative formation.

Specific and sensitive analytical methods have been developed for the measurement of antrafenine and its main acid metabolite, 2-([17-(trifluoromethyl)-4-quinolinyl] amino) benzoic acid (FQB), at therapeutic concentrations in plasma and urine. Following the addition of internal standards (the methyl ester of FQB and 2-([8-(trifluoromethyl)-4-quinolinyl] amino) benzoic acid) the parent drug and the metabolite were extracted from biological material with diethyl ether at a weakly acid pH. Drug extracts were evaporated to dryness prior to chromatographic analysis. Antrafenine was measured by high-performance liquid chromatography using a Spherisorb 5-micrometer ODS column with acetonitrile-0.1 M sodium acetate as the mobile phase. Samples were injected automatically using a 500-microliter injection loop. The detector wavelength was 353 nm corresponding to the maximum UV absorption of both drug and internal standard. The coefficient of variation (C.V.) for the determination of antrafenine concentrations between 5 and 250 ng/ml ranged between 24 and 3%, respectively. The acid metabolite of antrafenine was measured by gas-liquid chromatography with electron-capture detection using a 1 m column packed with 3% OV-225 on Gas-Chrom Q (100-120 mesh) at 240 degrees C and on-column methylation with trimethylphenyl ammonium hydroxide. The C. V. of the method for the analysis of metabolite concentrations between 10 and 500 ng/ml ranged between 3 and 9%, respectively.

Aminoquinolines↗
PubMed1982

Chromophoric determination of putrescine, spermidine and spermine with dabsyl chloride by high-performance liquid chromatography and thin-layer chromatography.

A fast and sensitive method for the determination of putrescine, spermidine, spermine and ammonia by high-performance liquid chromatography (HPLC) with dabsyl chloride is described. These compounds are converted to their chromophoric dabsyl derivatives and are separated by a normal-phase chromatographic column (mu Porasil, 10 microgram) with 2% acetone in chloroform as isocratic mobile phase. The sensitivity of the method is 20 pmoles. The present method was shown to be a straightforward procedure for estimating polyamines in various rat tissues. The chromophoric derivatives of polyamines are also well separated by thin-layer chromatography (TLC) on silica gel, and the combination of the HPLC and TL C procedures provides a reliable method for qualitative and quantitative analysis of polyamines.

Animals↗
PubMed1982

Analyses of nicotine and cotinine in tissues by capillary gas chromatography and gas chromatography-mass spectrometry.

Selective extraction and chromatographic techniques have been developed to measure low nanogram quantities of nicotine and cotinine in tissues. Analyses were performed by capillary column gas chromatography with a specific nitrogen-phosphorus detector and by gas chromatography-mass spectrometry. With close structural analogues for internal standards, high quantitative accuracy and precision were demonstrated for the range 5-1000 ng per g of tissue. The sensitivity limit was 2-3 ng/g for both compounds. The advantage of these techniques compared to previously published methods is increased selectivity; the other methods were developed for analysis of biological fluids and are not readily adaptable to more complex biological matrices such as tissue homogenates. With the newly developed techniques, we were able to perform a pharmacokinetic study of nicotine and cotinine in mouse liver following a single intraperitoneal injection of nicotine.

Animals↗