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At least 1,207 records · Page 67Linked to original sources
PubMed2001

Simulated cometary matter as a test for enantiomer separating chromatography for use on comet 46P/Wirtanen.

The Cometary Sampling and Composition Experiment on board of European Space Agency's cornerstone mission ROSETTA is designed to identify organic molecules in cometary matter in situ by a combined pyrolysis gas chromatographic and mass spectrometric technique. Its capillary columns coated with chiral stationary phases received considerable attention, because they are designed for separations of non-complex enantiomers to allow the determination of enantiomeric ratios of cometary chiral organic compounds and consequently to provide information about the origin of molecular parity violation in biomolecules. To get gas chromatographic access to organic compounds on the comet, where macromolecules and complex organic polymers of low volatility are expected to make up the main organic ingredients, the combination of two injection techniques will be applied. The pyrolysis technique performed by heating cometary samples stepwise to defined temperatures in specific ovens resulting in thermochemolysis reactions of polymers and a chemical derivatization technique, in which the reagent dimethylformamide dimethylacetal assists pyrolysis derivatization reactions in producing methyl esters of polar monomers. The combination of the reagent assisted pyrolysis gas chromatographic technique with enantiomer separating chromatography was tested with laboratory-produced simulated cometary matter.

Ammonia↗
PubMed1998

Intermembrane distance in multilamellar vesicles of phosphatidylcholine depends on the interaction free energy between solvents and the hydrophilic segments of the membrane surface.

To investigate the interaction of the surface of biomembranes with solvents systematically, we have studied the structure and phase behavior of multilamellar vesicles of dipalmitoylphosphatidylcholine (DPPC) and 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) in dimethylformamide (DMF)-water mixture by X-ray diffraction and differential scanning calorimetry. The solubility of phosphorylcholine, which is the same molecular structure as the head-group of phosphatidylcholine (PC), decreased with an increase in DMF concentration. This result indicates that DMF is a poor solvent for the hydrophilic segments of the surface of the PC membrane, and interaction free energy of the hydrophilic segments of the membrane surface with solvents increases with an increase in DMF concentration. X-ray diffraction data indicated that DPPC-MLVs were in the bilayer gel phase from 0 to 80% (v/v) DMF, and that the spacing (lamellar repeat period) and intermembrane distance of DPPC-MLV decreased with an increase in DMF concentration. Main transition temperature and pre-transition temperature of DPPC-MLV increased with an increase in DMF concentration, and above 50% (v/v) DMF there was no pre-transition. In the interaction of POPC-MLV with DMF, X-ray diffraction data indicated that POPC-MLVs were in L(alpha) phase (liquid-crystalline phase) from 0 to 80% (v/v) DMF, and that the spacing and intermembrane distance of POPC-MLV decreased with an increase in DMF concentration. These results are discussed by the change of the interaction free energy between the hydrophilic segments of the membrane surface and solvents. As DMF concentration increases, this interaction free energy may increase, resulting in the decrease of the intermembrane distance of PC-MLVs.

Journal Article↗
PubMed2001

In vitro bioassays for anticancer drug screening: effects of cell concentration and other assay parameters on growth inhibitory activity.

In vitro growth inhibition assays were performed using human cancer cell lines at various concentrations with experimental anticancer drugs such as the cryptophycins and other cytotoxins. The effect of variations in assay parameters on the observed growth inhibition of these anticancer therapeutic agents was determined. The results demonstrated that the observed inhibitory activity of these compounds varied inversely with the cell concentrations used. The observed differences in activity between different cytotoxins were not necessarily proportionate. Thus, the relative activities of two toxins also varied with cell concentration. Furthermore, the sensitivity of these cell lines to the cytostatic purine analog, 6-mercaptopurine (used as a control), varied with cell concentration as well. The activity of this compound was dependent on the medium used for cell growth, yielding good activity in Eagle's minimum essential medium, but not in Ham's F-12 (Kaigin) medium. Moreover, growth inhibition by cryptophycin as well as 6-mercaptopurine was also dependent on the serum concentration in the medium. Finally, the sensitivity of the cancer cell lines to various organic solvents commonly used as drug vehicles for in vitro testing, such as ethanol, dimethylformamide, and dimethylsulfoxide, was likewise found to vary inversely with cell concentration.

Antineoplastic Agents↗
PubMed1982

Glass capillary gas chromatography of the serum fatty acid fraction via automatic injection of lipid extracts.

The combination of a consecutive double capillary column gas chromatographic system (Deans type) with a fully automatic injection device was developed to determine quantitatively the fatty acid fraction of serum extracts, without prior removal of the other lipids. A major difficulty arose through ghosting (memory), via reaction of methylating reagents with lipid deposits, mainly in the injection port. Use of diazomethane circumvented this, as the reagent was easily removed prior to analysis. The combination methyl iodide--potassium carbonate, convenient handling of which requires coinjection of methyl iodide, proved to be less than completely dependable. Dimethylformamide dimethylacetal is completely out of the question as a coinjectant. Lipid deposits in the injection port produced peak area drifts which could, however, be counteracted. The apparatus is capable of analyzing samples completely unattended for at least 20 hours (80 samples). It has been operated non-stop, day and night, for between 4 and 7 days with occasional reloading and servicing.

Autoanalysis↗
PubMed1988

Determination of erythrocyte porphyrins by reversed-phase high-performance liquid chromatography using capsule-type silica gels coated with silicone polymer.

A simple, rapid and reliable method is described for determining erythrocyte porphyrins using a new type of reversed-phase silica whose surface is coated with silicone polymer. After a single-step extraction of blood with N,N-dimethylformamide, zinc protoporphyrin IX and protoporphyrin IX were separately quantified in a single run in 5 min. The column life was so long that no alteration in elution profile or retention time was apparent after 1500 injections of samples. The method described would be useful for the screening of lead exposure or iron-deficiency anaemia, and also for the diagnosis of erythropoietic protoporphyria.

Chromatography, High Pressure Liquid↗
PubMed1986

Comparative study of solid phase extraction techniques for isolation of leukotrienes from plasma.

We have compared five commercially available absorbent materials (i.e. C18 Sep-Pak, C18 J.T. Baker, Amberlites XAD-7, XAD-2 and XAD-4) for their applicability as effective tools for extraction of leukotrienes from plasma samples. Leukotriene C4 (LTC4) and B4 (LTB4) were selected as representatives of peptidic and non-peptidic leukotrienes, respectively. These leukotrienes were added to 1 ml of plasma and passed through columns containing the above described adsorbent materials. The recovery was determined for each material using different combinations of solvents. XAD-4 gave the highest recovery for LTB4 (90%), whereas XAD-4 and XAD-2 gave identical recoveries for LTC4 (90%) when an eluting solvent mixture of pyridine-water--dimethylformamide (50:45:5) was used. The efficiency of the other three solid adsorbent materials for leukotriene extraction were in order of decreasing magnitude, C18 J.T. Baker greater than XAD-7 greater than C18 Sep-Pak. XAD-7 was shown to be more efficient for LTB4 than for LTC4, whereas the octadecylsilane C18 materials gave approximately similar recoveries for both of the leukotrienes. In addition to very good extraction properties of XAD-4 and XAD-2 as compared to octadecylsilane silica, these solid adsorbent materials retained less plasma impurities than the C18 materials, giving cleaner chromatograms for leukotrienes extracted from plasma. Therefore, XAD-4 or XAD-2 are the best overall choice for extraction of leukotrienes from plasma for reversed-phase high-performance liquid chromatographic analysis.

Chromatography, High Pressure Liquid↗
PubMed1980

Gas chromatographic-mass spectrometric assay for low levels of retinoic acid in human blood.

A rapid and sensitive method of analysis for retinoic acid in human blood has been developed using gas chromatography-mass spectrometry for separation and detection. The retinoic acid is isolated by solvent extraction into petroleum ether, and converted to methyl retinoate by reacting with dimethylformamide dimethylacetal. The method has been applied to the study of retinoic acid in human blood after subtotal inunction, total inunction and intravenous injection of retinoic acid. The sensitivity limit of 1 ng/ml blood is realized with a 10-ml blood sample.

Female↗
PubMed1979

Analysis of fatty acids from human lipids by gas chromatography.

A rapid, quantitative method is described for the analysis of fatty acids from human lipids, namely serum lipids and lipids from adipose tissue biopsies. The method includes extraction of serum lipids with chloroform--methanol, hydrolysis with tetramethylammonium hydroxide, methylation with methyl iodide and N,N-dimethylformamide and gas chromatographic analysis on a Supelcoport SP-2320 column. Fat biopsies are analysed without extraction. Optimal hydrolysis conditions have been investigated.

Adipose Tissue↗
PubMed1989

Optimized determination of thiochrome derivatives of thiamine and thiamine phosphates in whole blood by reversed-phase liquid chromatography with precolumn derivatization.

A liquid chromatographic method involving precolumn derivatization for determining thiamine and its phosphate esters in human blood has been optimized. Blood sample stored at - 20 degrees C were haemolysed and deproteinized by perchloric acid. The supernatants of the samples were oxidized by addition of potassium ferricyanide-sodium hydroxide, and phosphoric acid was added to obtain a neutral pH in order to extend the column life. The samples were stable after derivatization for at least 24 h, if protected from light and kept at room temperature. Gradient separation with 140 mmol phosphate buffer (pH 7.0), and methanol, tert-butylammonium hydroxide and dimethylformamide as modifiers, on a 3-microns Chromsphere octadecylsilica column gave an analysis time of 15 min. The method was found to be very suitable for the determination of thiamine components in whole blood. The minimal detectable amount is 0.5 nmol/l and the method is linear to at least 1000 nmol/l. The recovery (98 +/- 3%) and precision are very good.

Chromatography, Liquid↗
PubMed1986

High-performance liquid chromatographic analysis of glutathione and its thiol and disulfide degradation products.

A rapid and sensitive high-performance liquid chromatographic method for quantitation of picomole levels of glutathione, glutathione disulfide, cysteine, cystine, cysteinylglycine, cysteinylglycine disulfide and cysteine glutathione-mixed disulfide in biological samples is described. The compounds were separated isocratically on a reversed-phase column by ion-pair chromatography. The mobile phase consisted of an aqueous buffer containing 0.1 M monochloroacetic acid and 3.3 mM 1-heptanesulfonic acid (pH 2.60)-methanol-N,N-dimethylformamide (96.5:3.0:0.5). After chromatographic separation, the disulfides were reduced by a potential (-1.0 V) from a battery, with subsequent detection of all thiols by electrochemical oxidation (+0.15 V) with a dual gold-mercury electrode. Thiol and disulfide concentrations were determined in tissue extracts (liver and kidney) and fluids (bile and plasma) from control rats and rats treated with acivicin, an inhibitor of gamma-glutamyltranspeptidase. A marked increase in biliary glutathione concentration was observed in treated animals with a corresponding decrease in cysteine and cysteinylglycine concentrations. The results demonstrate that this method is useful for measuring glutathione and its degradation products in tissues and fluids.

Animals↗
PubMed1983

Purification of salt-soluble cross-linked elastin by hydrophobic interaction chromatography.

The hydrophobic protein elastin, which is a major constituent of vascular and lung tissue is fragmented in several pathological conditions. The nature of the soluble fragments is not well understood. Such fragments bind to alkyl chains linked to agarose. Elution, which is effected by dimethylformamide and sodium dodecyl sulphate, is optimal from the decyl-agarose column. Dialysis of the eluates against buffered sodium chloride precipitates elastin, thus further purifying the salt-soluble cross-linked elastin.

Amino Acids↗
PubMed2002

Measurement of urinary N-acetyl-S-(N-methylcarbamoyl)cysteine by high-performance liquid chromatography with direct ultraviolet detection.

A new high-performance liquid chromatographic (HPLC) method is described for the determination of urinary N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC), the final product of the conjugation reaction between a metabolic intermediate of N,N-dimethylformamide (DMF) and glutathione. Urine samples were purified by C(18) solid-phase extraction and then directly analysed by HPLC with an Aminex Ion Exclusion HPX-87H column maintained at 25 degrees C and a UV detector set at 196 nm. Under isocratic conditions (2.4 mM sulphuric acid, flow-rate=0.6 ml/min) AMCC eluted at 20.2 min. The reproducibility (C.V.%) was 1.3-2.7% (intra- and inter-assay, N = 5); the accuracy was 98.0+/-1.7% at 10 mg/l and 101.9+/-1.5% at 800 mg/l (mean+/-SD, N = 3). AMCC was measured in urine from 22 exposed subjects. A strong correlation was found between AMCC and environmental DMF [AMCC (mg/g creatinine)=3.40xDMF (mg/m(3)) + 3.07; r=0.95], while in the urine of 20 unexposed subjects the concentration of AMCC was constantly below the detection limit of the method (0.9 mg/l in urine). The method described appears to be useful for the biological monitoring of DMF exposure.

Acetylcysteine↗
PubMed1998

High-performance liquid chromatographic method for measuring total plasma homocysteine levels.

We have modified a high-performance liquid chromatographic (HPLC) procedure based on SBD-F (ammonium-7-fluorobenzo-2-oxa-1,3-diazole-4-sulphonate) pre-column derivatization to obtain an assay that is useful for routine clinical total plasma homocysteine (tHcy) analysis. The introduction of easily handled sodium borohydride instead of the traditional tri-n-butylphosphine in dimethylformamide as a reductant and a 14-min run-time using basic isocratic HPLC equipment are the more notable advantages. The addition of mercaptopropionylglycine as an internal standard contributed to improvements in the reproducibility of the assay, yielding within- and between-run precisions of 1.9 and 4% (C.V.), respectively. Reference values for fasting tHcy were 7.65+/-2.3 and 8.9+/-2.4 micromol/l, while post-methionine load gave tHcy levels of 19.9+/-5.5 and 26.8+/-5.5 micromol/l, for women and men, respectively (n=40).

Chromatography, High Pressure Liquid↗
PubMed1999

Improved high-performance liquid chromatography determination of methotrexate and its major metabolite in plasma using a poly(styrene-divinylbenzene) column.

A sensitive high-performance liquid chromatographic assay has been developed for measuring plasma concentrations of methotrexate and its major metabolite, 7-hydroxymethotrexate. Methotrexate and metabolite were extracted from plasma using solid-phase extraction. An internal standard, aminopterin was used. Chromatographic separation was achieved using a 15-cm poly(styrene-divinylbenzene) (PRP-1) column. This column is more robust than a silica-based stationary phase. Post column, the eluent was irradiated with UV light, producing fluorescent photolytic degradation products of methotrexate and the metabolite. The excitation and emission wavelengths of fluorescence detection were at 350 and 435 nm, respectively. The mobile phase consisted of 0.1 M phosphate buffer (pH 6.5), with 6% N,N-dimethylformamide and 0.2% of 30% hydrogen peroxide. The absolute recoveries for methotrexate and 7-hydroxymethotrexate were greater than 86%. Precision, expressed as a coefficient of variation (n=6), was <10% at each of five methotrexate concentrations in the range 2.5-50 ng/ml. The limits of quantitation of methotrexate were 1 and 2.5 ng/ml for methotrexate and 7-hydroxymethotrexate, respectively (using 1 ml plasma). A robust HPLC method has been developed for the reproducible quantitation of methotrexate in plasma of patients taking a weekly dose of methotrexate for rheumatoid arthritis.

Antimetabolites, Antineoplastic↗
PubMed2000

Effect of solvent on the preparation of surfactant-free poly(DL-lactide-co-glycolide) nanoparticles and norfloxacin release characteristics.

The surfactant-free nanoparticles of poly(DL-lactide-co-glycolide) (PLGA) were prepared by dialysis method without surfactant and physicochemical properties such as particle size and drug contents were investigated against used initial solvent. The size of PLGA nanoparticles and drug contents were significantly changed by used initial solvent. The size of PLGA nanoparticles prepared from dimethylacetamide (DMAc), dimethylformamide (DMF), and dimethylsulfoxide (DMSO) as a initial used solvent was smaller than that of acetone. Selected initial solvent used to dissolve the copolymer significantly affects the size of nanoparticles and drug contents. It was shown that PLGA nanoparticles have spherical shapes from the results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. It was thought that surfactant-free nanoparticles of PLGA entrapping norfloxacin (NFX) has nice drug loading capacity without free-drug on the surface of nanoparticles through the analysis of X-ray powder diffraction. From these results, it was showed the potential that the PLGA nanoparticles could be formed successively by dialysis method without surfactant. Release kinetics of NFX used as a model drug was governed by not only drug contents but also particle size parameter. The higher the drug contents and the larger the particle size resulted in slower the drug release.

Anti-Infective Agents↗
PubMed2001

Examination of oxidized cellulose as a macromolecular prodrug carrier: preparation and characterization of an oxidized cellulose-phenylpropanolamine conjugate.

The purpose of this study was to investigate the use of 6-carboxycellulose (OC), a biocompatible and bioresorbable polymer, as a prodrug carrier for amine drugs. Phenylpropanolamine hydrochloride (PPA.HCl) was used as a model drug. OC and PPA were reacted in dimethylformamide (DMF) in the presence of 1,3-dicyclohexylcarbodiimide (DCC) for 2.5 days at room temperature. Filtration, followed by washing with methanol, and subsequent drying under vacuum, produced the conjugate in 65-78% yield. The amount of PPA in the product, determined from the difference in the carboxylic content before and after the reaction, was 24.2% (w/w), corresponding to a degree of substitution (DS) value of 0.7. The Fourier transform-infra red (FT-IR) spectrum of the conjugate, compared with that of OC and PPA.HCl, showed a new band at about 1533 cm(-1) attributable to a C = O (amide II) stretching and N single bond H (amide I and amide II) bending vibrations, a decrease in intensity of the characteristic free carboxylic acid carbonyl stretching band at about 1748 cm(-1), and a strong band at 1663 cm(-1) due to C = O (amide I) stretching vibration, suggesting that the OC is linked to PPA via an amide bond. The solid-state carbon-13 cross polarization/magic angle spinning nuclear magnetic resonance ((13)CCP/MAS NMR) spectrum of the conjugate was also consistent with this structure. The release studies performed in pH 4.5, 5.5, and 7.4 buffer solutions and in rat liver homogenate (pH 7.4), showed the conjugate to be more susceptible to hydrolysis at a lower pH and in the presence of rat liver homogenate. In conclusion, the results presented show that OC can be covalently linked to amine drugs via an amide bond in DMF using DCC as a coupling agent, and provide a macromolecular prodrug delivery system.

Cellulose↗
PubMed2001

Analysis of glimepiride by using derivative UV spectrophotometric method.

Glimepiride (Amaryl), which is a new oral antidiabetic drug in the sulfonylurea class, was analysed by using second order derivative UV spectrophotometry. The quantification of glimepiride in dimethylformamide was performed in the wavelength range of 245-290 nm at N = 6, ?lambda = 21. The second order derivative spectra was calculated using peak to peak (lambdaDMF = 263.3-268.2 nm), peak to zero (lambdaDMF = 268.2 nm) and tangent (lambdaDMF = 263.3-271.8 nm) method for calibration curves, the linearity range of 1.00-500.00 microg ml(-1) by using the second order derivative UV spectrophotometric method. The developed method was applied to directly and easily to the analysis of the pharmaceutical tablet preparations. R.S.D. were found to be 4.18% (Amaryl tablet; 1 mg) and 2.21% (Amaryl tablet; 2 mg). The method was completely validated and proven to be rugged. The limit of quantitation and the limit of detection were found as 1.00 and 0.4 microg ml(-1), respectively. This validated derivative UV spectrophotometric method is potentially useful for a routine laboratory because of its simplicity, rapidity, sensitivity, precision and accuracy.

Drug Stability↗
PubMed2002

Voltammetric determination of fenbendazole in veterinarian formulations.

A versatile voltammetric method for quantitative determination of fenbendazole (FBZ) in commercial tablets has been proposed, where direct dissolution of tablets is carried out in 0.1 mol l(-1) tetrabutylamoniun tetrafluorborate containing dimethylformamide solutions. Linear sweep (LSV), square wave (SWV) and differential pulse (DPV) voltammetry techniques were applied to study FBZ at a glassy carbon electrode, exhibiting a well defined irreversible oxidation peak at 1.15 V vs. SCE. This methodology allows a precise quantitative determination of FBZ presenting detection limits of 5.2 x 10(-5) (LSV), 5.0 x 10(-6) (DPV) and 5.0 x 10(-5) mol l(-1) (SWV).

Electrochemistry↗