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At least 523 records · Page 29Linked to original sources
PubMed1997

Detection of microbial-derived fatty acids in carious dentin by gas chromatography and gas chromatography-mass spectrometry.

The aim of the present study was to analyze the fatty acid content of carious and sound human dentin. Gas chromatography and gas chromatography-mass spectrometry revealed the presence of fatty acids of C10-C18 size in the carious dentin, whereas fatty acids of C16 size were present in minute amounts in three samples of the corresponding sound dentine controls. No fatty acids were detected in the other sound dentin control samples. The source of fatty acids was considered to be microorganisms invading the dentin during the progression of the caries lesion. The presence of bacterial fatty acids in carious dentin may serve as a marker for the pathological process and thus contribute to the understanding of the mechanisms involved.

Dental Caries↗
PubMed1998

Analysis of methaqualone in biological matrices by micellar electrokinetic capillary chromatography. Comparison with gas chromatography-mass spectrometry.

The analysis of methaqualone (MTQ) in biological matrices by capillary electrophoresis (CE) is described. This methods uses liquid-liquid extraction and micellar electrokinetic capillary chromatography (MECC), an operation mode of CE. Separations are made using a 25 cm long capillary and a borate/phosphate buffer at pH 8.2. Using gas chromatography with mass spectrometry detection (GC-MS) as reference method, MTQ has been analyzed in urine, blood, gastric content and hair. For hair analysis, supercritical fluid extraction was compared with liquid-liquid extraction. Linearity was established in urine and blood between 0.25 and 10.0 micrograms/ml. MTQ recovery from blood was estimated at 60%. The limit of detection of this method in urine is about 0.10 microgram/ml. Drawbacks and advantages of MECC over GC-MS are discussed.

Blood Chemical Analysis↗
PubMed2002

Identification of incurred sulfonamide residues in eggs: methods for confirmation by liquid chromatography-tandem mass spectrometry and quantitation by liquid chromatography with ultraviolet detection.

Two complementary methods for identifying and measuring sulfonamide residues in eggs were developed for use in surveying eggs for potential drug residues. The first method uses liquid chromatography-tandem mass spectrometry (LC-MS-MS) to confirm the presence of sulfonamide residues in eggs. During its validation the limit of confirmation was estimated to be 5-10 ng/g (ppb) depending on the drug. Also, a method for measuring residue level by liquid chromatography with ultraviolet detection (LC-UV) was validated using the same extraction procedure as the confirmatory method. The determinative method was validated over the 50-200 ppb range. Samples were prepared by homogenizing whole egg, extracting with acetonitrile, and cleaning up with a C(18) solid-phase extraction cartridge. For confirmation, analytes were separated by gradient LC on a C(18) column, ionized by electrospray ionization (ESI), and detected by MS-MS with an ion trap mass spectrometer. For determination, analytes were separated by a different gradient LC procedure and detected by UV at 287 nm. Fifteen drugs were dosed individually in laying hens, and residues of parent drug and/or metabolites were found in eggs for all the drugs. Validation was based on repetitive analyses of control samples, control samples fortified at 100 ppb sulfonamides, and samples of blended incurred eggs.

Animals↗
PubMed1994

Predictive steady-state chromatography. 1. Algorithms for leading and trailing edges of resolved and unresolved peaks in liquid chromatography.

This paper describes mathematical models and curve-fitting procedures that permit steady-state saturation signals to be computed accurately from data along leading and trailing edges of liquid chromatograms. This new approach to quantitative chromatography is called predictive steady-state chromatography (PSSC). It is shown that the computed saturation signals are virtually the same when determined from data along leading and trailing edges and they vary linearly with analyte concentration. Most importantly, the computed saturation signals for a given analyte concentration are virtually independent of experimental variables such as sample volume and flow rate. For example, for sample volumes between 25 and 45 microL, the average computed saturation signal for a 0.025 mM solution of theophylline was 0.11 V with a standard deviation of 0.00097 V (RSD = 0.8%); similar results were found for other concentrations and for changes in flow rate. Dependencies of the PSSC method on sample volume and flow rate were compared with dependencies for peak-height and peak-area methods by using relative error coefficients. Dependencies on sample volume were 0.04%/microL for the PSSC method and 3 and 4%/microL for peak-height and peak-area methods, respectively. Dependencies on flow rate were 2%/mL/min for the PSSC method and 17 and 120%/mL/min for the peak-height and peak-area methods, respectively. Thus, the predictive steady-state method is 10-100-fold more rugged than peak-height and peak-area methods.

Algorithms↗
PubMed2005

A multidimensional differential proteomic platform using dual-phase ion-exchange chromatography-polyacrylamide gel electrophoresis/reversed-phase liquid chromatography tandem mass spectrometry.

Differential proteomic analysis has arisen as a large-scale means to discern proteome-wide changes upon treatment, injury, or disease. Tandem protein separation methods are required for large-scale differential proteomic analysis. Here, a novel multidimensional platform for resolving and differentially analyzing complex biological samples is presented. The platform, collectively termed CAX-PAGE/RPLC-MSMS, combines biphasic ion-exchange chromatography with polyacrylamide gel electrophoresis for protein separation, quantification, and differential band targeting, followed by capillary reversed-phase liquid chromatography and data-dependent tandem mass spectrometry for quantitative and qualitative peptide analysis. CAX-PAGE provides high protein resolving power with a theoretical peak capacity of 3570, extendable to 7600, a wide protein mass range verified from 16 to 273 kDa, and reproducible differential sample comparison without the added expense of fluorescent dyes and imaging equipment. Demonstrated using a neuroproteomic model, CAX-PAGE revealed an increased number of differential proteins, 137, compared with 82 found by 2D difference gel electrophoresis. When combined with RPLC-MSMS for protein identification, an additional quantification step is performed for internal validation, confirming a 2-fold or greater change in 89% of identified differential targets.

Animals↗
PubMed2006

Adsorption mechanisms and effect of temperature in reversed-phase liquid chromatography. meaning of the classical Van't Hoff plot in chromatography.

The effect of temperature on the adsorption and retention behaviors of a low molecular weight compound (phenol) on a C18-bonded silica column (C18-Sunfire, Waters) from aqueous solutions of methanol (20%) or acetonitrile (15%) was investigated. The results of the measurements were interpreted successively on the basis of the linear (i.e., overall retention factors) and the nonlinear (i.e., adsorption isotherms, surface heterogeneity, saturation capacities, and equilibrium constants) chromatographic methods. The confrontation of these two approaches confirmed the impossibility of a sound physical interpretation of the conventional Van't Hoff plot. The classical linear chromatography theory assumes that retention is determined by the equilibrium thermodynamics of analytes between a homogeneous stationary phase and a homogeneous mobile phase (although there may be two or several types of interactions). From values of the experimental retention factors in a temperature interval and estimates of the activity coefficients at infinite dilution in the same temperature interval provided by the UNIFAC group contribution method, evidence is provided that such a retention model cannot hold. The classical Van't Hoff plot appears meaningless and its linear behavior a mere accident. Results from nonlinear chromatography confirm these conclusions and provide explanations. The retention factors seem to fulfill the Van't Hoff equation, not the Henry constants corresponding to the different types of adsorption sites. The saturation capacities and the adsorption energies are clearly temperature dependent. The temperature dependence of these characteristics of the different assorption sites are different in aqueous methanol and acetonitrile solutions.

Adsorption↗
PubMed2006

Evaluation of the botanical authenticity and phytochemical profile of black cohosh products by high-performance liquid chromatography with selected ion monitoring liquid chromatography-mass spectrometry.

Black cohosh (Actaea racemosa L., syn. Cimicifuga racemosa L.) has become increasingly popular as a dietary supplement in the United States for the treatment of symptoms related to menopause, but the botanical authenticity of most products containing black cohosh has not been evaluated, nor is manufacturing highly regulated in the United States. In this study, 11 black cohosh products were analyzed for triterpene glycosides, phenolic constituents, and formononetin by high-performance liquid chromatography-photodiode array detection and a new selected ion monitoring liquid chromatography-mass spectrometry method. Three of the 11 products were found to contain the marker compound cimifugin and not cimiracemoside C, thereby indicating that these plants contain Asian Actaea instead of black cohosh. One product contained both black cohosh and an Asian Actaea species. For the products containing only black cohosh, there was significant product-to-product variability in the amounts of the selected triterpene glycosides and phenolic constituents, and as expected, no formononetin was detected.

Chromatography, High Pressure Liquid↗
PubMed2001

Simultaneous ion-exclusion chromatography and cation-exchange chromatography of anions and cations in environmental water samples on a weakly acidic cation-exchange resin by elution with pyridine-2,6-dicarboxylic acid.

A non-suppressed conductivity detection ion chromatographic method using a weakly acidic cation-exchange column (Tosoh TSKgel OApak-A) was developed for the simultaneous separation and determination of common inorganic anions (Cl-, NO3- and SO4(2-)) and cations (Na+, NH4+, K+, Mg2+ and Ca2+). A satisfactory separation of these anions and cations on the weakly acidic cation-exchange column was achieved in 25 min by elution with a mixture of 1.6 mmol L-1 pyridine-2,6-dicarboxylic acid and 8.0 mmol L-1 18-crown-6 at flow rate of 1.0 mL min-1. On this weakly acidic cation-exchange resin, anions were retained by an ion-exclusion mechanism and cations by a cation-exchange mechanism. The linear range of the peak area calibration curves for all analytes were up to two orders of magnitude. The detection limits calculated at S/N = 3 ranged from 0.25 to 1.9 mumol L-1 for anions and cations. The ion-exclusion chromatography-cation-exchange chromatography method developed in this work was successfully applied to the simultaneous determination of major inorganic anions and cations in rainwater, tap water and snow water samples.

Chromatography, Ion Exchange↗
PubMed2003

Quantitative liquid chromatography-mass spectrometry determination of catechins in human plasma by automated on-line extraction using turbulent flow chromatography.

A simple, fast and sensitive liquid chromatography-mass spectrometry (LC-MS) method with automated on-line extraction using turbulent flow chromatography (TFC) for the determination of five catechins in human plasma was developed. In this method, after on-line extraction by its injection onto an extractor column at turbulent flow, five catechins were backwashed onto a reversed phase column via on-line column switching and separated chromatographically at a laminar flow of 1 ml min(-1). Using this tandem LC-LC-MS system, the extraction, the separation and the quantitation of five catechins in human plasma could be achieved with satisfactory selectivity and sensitivity. The limit of detection (S/N = 3) ranged from 0.6 to 2 ng ml(-1). The described procedure was very simple and rapid since no off-line sample preparation was required, total analysis time being 18.5 min.

Catechin↗
PubMed1978

Affinity chromatography of trypsin and related enzymes. V. Basic studies of quantitative affinity chromatography.

A detailed study of the quantitative affinity chromatography of trypsin [EC 3.4.21.4] is reported here. Frontal chromatography using an enzyme solution of very low concentration on an affinity adsorbent gave the dissociation constant of the enzyme-immobilized ligand complex (Kd). Kd values determined under various conditions enabled us to discuss in detail the interaction of trypsin and affinity adsorbents (mainly Gly-Gly-Arg Sepharose). The pH dependence of Kd was consistent with that of the interaction of trypsin and product-type compounds. The effects of changes in temperature, ionic strength, dielectric constant, etc., were also studied. The Ki values of soluble competitive inhibitors can be determined by analysis of their effects on the elution volume of the enzyme. The values obtained were in good agreement with those obtained by kinetic analysis. The present method proved to be useful as a general procedure to investigate the interaction of a protein and a specific ligand.

Arginine↗
PubMed2002

Chromatographic screening for zopiclone and metabolites in urine using liquid chromatography and liquid chromatography-mass spectrometry techniques.

Zopiclone is a benzodiazepine-like hypnotic that was believed not to have any abuse potential. Nevertheless, during the past few years there have been an increasing number of reports on the abuse and misuse of zopiclone. Despite this, methods for screening analysis in urine are lacking. To investigate whether UV detection would be possible to use for this purpose, a liquid chromatography method with ultraviolet detection for analyzing zopiclone and its urinary metabolites was developed, with liquid chromatography-mass spectrometry for confirmation. The method was used for analyzing samples from subjects receiving methadone. The limits of detection were approximately 100 ng/mL in control urine samples and 500 ng/mL in urine samples from subjects receiving methadone. However, due to the high background in these patients' urine, a single therapeutic dose was impossible to detect.

Adult↗
PubMed2002

Characterization by liquid chromatography-nuclear magnetic resonance spectroscopy and liquid chromatography-mass spectrometry of two coupled oxidative-conjugative metabolic pathways for 7-ethoxycoumarin in human liver microsomes treated with alamethicin.

The microsomal metabolism of 7-ethoxycoumarin (7-EC) was investigated using liquid chromatography (LC)-NMR and liquid chromatography-mass spectrometry (LC-MS) to characterize the coupling of oxidative-conjugative metabolism events. Within microsomes, cytochromes P450 (P450s) and UDP-glucuronosyltransferases (UGTs) are spatially disparate, each having surface and luminal localization, respectively. To optimize cofactor and substrate transit to UGT without compromising P450 activity, the pore-forming peptide alamethicin was used for microsomal perforation. Aqueous extracts of microsomal incubations containing NADPH and UDP-glucuronic acid were injected for LC-NMR and LC-MS analysis. The analytical complementarity of LC-NMR and LC-MS permitted the identification of four metabolites (M1 to M4). The metabolites M1 and M2 are novel microsomal metabolites for 7-EC, consistent with 3-hydroxylation and subsequent glucuronidation, respectively. Metabolites M3 and M4 were 7-hydroxycoumarin (7-HC) and 7-HC glucuronide, respectively. Viewed collectively, these results illustrate the utility of alamethicin in the examination of coupled oxidative-conjugative metabolism and the synergy of LC-NMR and LC-MS in metabolite identification.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1967

Identification of fatty acids and aliphatic hydrocarbons in Sarcina lutea by gas chromatography and combined gas chromatography-mass spectrometry.

The composition and nature of the fatty acids and hydrocarbons of Sarcina lutea were elucidated by gas chromatography and by combined gas chromatography-mass spectrometry. The distribution of fatty acids found in S. lutea showed two families of pairs, or dyads, of saturated monocarboxylic acids (C12-C18) with and without methyl branching. These pairs of fatty acids showed a pattern of iso and anteiso structures for C13, C15, and C17, and iso and normal structures for C12, C14, and C16. Only the C18 showed unsaturation. The distribution of hydrocarbons in the range C22-C29 showed two families of tetrads of unsaturated aliphatic hydrocarbons all showing methyl branching. Each tetrad was composed of four isomers identified as two iso olefins and two anteiso olefins. The only difference between the tetrads pertaining to different families was found in the relative gas chromatographic retention times of the last two components of each group.

Chromatography, Gas↗
PubMed2004

[An unusual type of the chromatography profile of blood serum carbohydrates in the diagnosis of deep mycosis by gas and liquid chromatography].

The paper contains a description of a diagnosis method (now under elaboration) applicable to human mycosis, which is based on a high-sensitivity gas-liquid chromatography. According to the study results, despite its promising nature, the method in question is not accurate enough in terms of a precise diagnosis of invasive candidosis in oncology patients. The authors point out that the chromatography-diagnosis results need now a histological confirmation.

Acute Disease↗
PubMed2004

[Study on thermostability and photo-isomerization of trans-resveratrol by high performance liquid chromatography and liquid chromatography-electrospray ionization-mass spectrometry].

The thermostability and photo-isomerization reaction mechanism of trans-resveratrol were studied by using high performance liquid chromatography (HPLC) and liquid chromatography-electrospray ionization-mass spectrometry ( LC-ESI-MS). A reversed-phase Hypersil-ODS column was used with the mobile phase consisting of 60/40 methanol-water, with addition of 0.05% trifluoroacetic acid for HPLC, and 0.1% formic acid and 5 mmol/L ammonium formate for LC-ESI-MS, at a flow rate of 0.5 mL/min. Diode array detection was set at 300 nm and the injection volume was 20 or 10 microL. Mass spectrometric conditions were in the negative mode. The results of thermostability test under 4, 20 and 40 degrees C indicated that the concentration of trans-resveratrol, after storage for 600 h, was decreased slightly under 4 degrees C, decreased by 5% under 20 degrees C, and 10% under 40 degrees C. In addition, the photo-isomerization reaction of trans- and cis-resveratrol under 254 nm and 365 nm UV irradiation was investigated by LC-ESI-MS, showing that the isomerization is based on p-status, and that some secondary reactions are radical induced.

Chromatography, High Pressure Liquid↗
PubMed2005

Liquid chromatography-mass spectrometric and liquid chromatography-tandem mass spectrometric determination of hallucinogenic indoles psilocin and psilocybin in "magic mushroom" samples.

Accurate and sensitive analytical methods for psilocin (PC) and psilocybin (PB), tryptamine-type hallucinogens contained in "magic mushrooms," were investigated using liquid chromatography-mass spectrometry (LC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS-MS). The chromatographic separation on an ODS column and mass spectral information gave complete discrimination between PC and PB without derivatization. The mass spectrometric detection had a high sensitivity, and the tandem mass spectrometric detection provided more specificity and accuracy, as well as high sensitivity. The detection limits ranged from 1 to 25 pg by LC-MS in the selected ion monitoring mode, and the intra- and inter-day coefficients of variation were estimated to be 4.21-5.93% by LC-MS-MS in the selected reaction monitoring mode. By applying the present LC-MS-MS technique to four real samples, the contents of PC and PB were found to vary over a wide range (0.60-1.4 and 0.18-3.8 mg/g dry wt. for PC and PB, respectively) between samples.

Agaricales↗
PubMed1979

Application of gel permeation chromatography and nonaqueous reverse phase chromatography to high pressure liquid chromatographic determination of retinyl palmitate and beta-carotene in oil and margarine.

A high pressure liquid chromatographic method was developed using high pressure gel permeation chromatography (HP-GPC) and high pressure reverse phase chromatography (RP-HPLC) for quantitation of retinyl palmitate and beta-carotene. HP-GPC was used for fractionation of vitamin A active compounds from oil preliminary to quantitation on nonaqueous RP-HPLC. HP-GPC fractionation was completed on oil and margarine dissolved in methylene chloride by 2 elution passes through 2 muStyragel (100 angstrom) columns connected in series with methylene chloride as the mobile phase. RP-HPLC separation of retinyl palmitate and beta-carotene was achieved on muBondapak C18 (10 micrometers), using methylene chloride-acetonitrile (30+70). Based on 10 repetitive analyses, recoveries of added beta-carotene and retinyl palmitate from vegetable oils were 98.6+/-2.9 and 95.2+/-2.6%, respectively. The coefficients of variation were 2.9% for beta-carotene and 2.7% for retinyl palmitate. The determination of vitamin A activity in 7 margarine brands with label claims of 10% U.S.RDA/serving revealed that all but one of the margarines contained at least 94% of the label claim. Vitamin A activity in the margarines ranged from 90.6 to 110.8% of the label declaration.

Carotenoids↗
PubMed1975

[The role of ionic equilibria in the separation of amino acids by thin layer chromatography, and the combination of electrophoresis and chromatography for high resolution].

Authors show the benefical effects of ionic equilibria in aminoacids partition chromatography in the particular case of a very high resolution system associating electrophoresis and thin layer chromatography: 1 N formic acid, tert-butanol/methanol/pyridine/formic acid/water (330:430:96:4:200), cellulose powder.

Amino Acids↗