Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “DIMETHYLFORMAMIDE”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

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

Preferential solvation of a dicyanate ester monomer and poly(sulfone) in different organic solvents by size-exclusion chromatography.

Preferential solvation parameters A in the ternary systems solvent (1) -monomer (2) -polymer (3) were determined as a tool to measure the compatibility between the cyanate ester monomer Arocy B10 and poly(sulfone), PSF, in the presence of three organic solvents: tetrahydrofuran, dimethylformamide and dicloromethane. The A parameter was measured by size-exclusion chromatography at different monomer-to-polymer ratios. The quantitative evaluation was rigorously made at polymer-diluted conditions. PSF was found to be preferentially solvated by the monomer. Concerning the solvent used, systems containing tetrahydrofuran showed the strongest solvation, the lowest A values being those obtained in dicloromethane. These results were in accordance with the intrinsic viscosity values of the PSF-solvent systems. The variation of A values with the Arocy B10 concentration is strongly dependent upon the nature of the solvent.

Chromatography, Gel↗
PubMed1977

[Contribution to the standardization of results in paper and thin-layer chromatography (author's transl)].

Chromatographic indexes that facilitate a better reproducibility of paper chromatographic results have been proposed, using the homologous series of coloured derivatives of secondary amines as standard substances. When using dimethylformamide as the stationary phase the value of the indexes proved to be independent of the concentration of the impregnating solution of the stationary phase, of the temperature changes during the chromatographic process, of the ways of impregnation and of the skills of workers. It depends only on the type of the stationary phase and on the composition of the mobile phase. The obtained indexes can contribute to a better reproducibility of RF values and to an easier and more objective identification of substances.

Alcohols↗
PubMed1986

Stability-indicating liquid chromatographic determination of cephapirin, desacetyl cephapirin and cephapirin lactone in sodium cephapirin bulk and injectable formulations.

A specific, stability-indicating, high-performance liquid chromatographic assay was developed for the determination of cephapirin, desacetyl cephapirin and cephapirin lactone in sodium cephapirin (cefadyl) bulk and injectables. The procedure uses a muBondapak C18 column and a mobile phase of dimethylformamide-acetic acid-potassium hydroxide in water. UV detection at 254 nm is used for quantitation with acetanilide used as the internal standard. The assay is precise, accurate and linear over the range of 100-300 micrograms/ml for cephapirin and over the range of 2-6 micrograms/ml for desacetyl cephapirin and cephapirin lactone. The assay is also stability-indicating for the described thermal, acid, base, aqueous and accelerated light degradations.

Cephalosporins↗
PubMed1977

Preparation, gas chromatography and mass spectrometry of methyl and trimethylsilyl esters of indomethacin.

The preparation and gas chromatographic-mass spectrometric behavior of the methyl and trimethylsilyl esters of indomethacin, 1-(p-chlorobenzoyl)-5-methoxy-2-methylindole-3-acetic acid, are described. Reaction of this anti-inflammatory drug with diazomethane or bis(trimethylsilyl)acetamide forms the expected esters. Derivatization with dimethylformamide dimethylacetal yields two compounds, the methyl ester (major product) and a methyl ester-dimethylaminomethylene condensation (at the alpha-carbon of the side chain) product (minor). Experiments with 5-O-desmethyl-indomethacin have demonstrated that using the described diazomethane methylation conditions no alkylation of the phenolic group occurs. Esterification combined with an isolation procedure allows the determination of indomethacin levels in plasma and aqueous humor of rabbits, the 4-fluorobenzoyl analog serving as internal standard. The derivatives exhibit excellent electron capture properties allowing quantitative assay of the drug at the submicrogram level. Precision and accuracy for plasma samples varied from 92 +/- 19% (5 ng/ml) to 96 +/- 1.5% (1000 ng/ml). The analogous values for aqueous humor are superior: 97 +/- 5.6% and 99 +/- 2.2%, resectively.

Chromatography, Gas↗
PubMed1987

Effects of organic solvents on the partitioning of enzymes in aqueous two-phase systems.

Organic solvents (ethylene glycol, glycerol, dimethyl sulphoxide, dimethylformamide, dioxane, methanol and propanol-2, as well as sucrose and urea) have been included in aqueous two-phase (liquid-liquid) systems comprised of water, dextran and poly(ethylene glycol). The concentration of the organic solvent was in most cases 20% (w/w). The influence of these solvents on the phase-forming properties, the volume ratio, the freezing point and the partitioning of a polymer-bound ligand, Procion Red HE-3B poly(ethylene glycol), has been studied. The partition coefficients for alkaline phosphatase decrease with ethylene glycol, glycerol, sucrose and urea (factors of 0.25-0.5), but increase with the other substances (factors of 1.2-1.6). The temperature effects on the partitioning of alkaline phosphatase from calf intestine as well as of phosphofructokinase from yeast in systems containing ethylene glycol have been studied and compared with partitioning in standard systems, not containing solvents. The possible uses of the above systems for partitioning studies of enzymes are discussed.

Alkaline Phosphatase↗
PubMed1987

Analysis of amino acids by gas-liquid chromatography as tert.-butyldimethylsilyl derivatives. Preparation of derivatives in a single reaction.

The effect of temperature, solvent and reagents on the formation of the N(O)-dimethyl-tert.-butylsilyl derivatives of proteic amino acids has been studied. Quantitative silylation is achieved using dimethyl-tert.-butylsilyltrifluoroacetamide with 1% tert.-butyldimethylchlorosilane in dimethylformamide by heating at 75 degrees C for 30 min. Two peaks were obtained for arginine under these conditions. However, most of the standard proteic amino acids can be assayed. The N(O)-dimethyl-tert.-butylsilyl derivatives of the proteic amino acids have been analysed by gas chromatography-mass spectrometry using the methane chemical ionization mode. The spectral data are presented and have been used to confirm the structures of the amino acid derivatives.

Amino Acids↗
PubMed1984

One-step isocratic high-performance liquid chromatographic purification of radioiodinated and radioiodinated-photoactivable derivatives of cholecystokinin.

N-Hydroxysuccinimidyl-3-(4-hydroxy-3-[125I]iodophenyl)propionate (the Bolton-Hunter reagent) was conjugated with (Thr 34, NLeu 37) cholecystokinin (CCK) 31-39 in anhydrous dimethylformamide-pyridine in 20% yield. The radiolabelled peptide was purified from the reaction mixture in one step, by isocratic elution from a C18 high-performance liquid chromatographic (HPLC) column with 35% aqueous acetonitrile-0.13% heptafluorobutyric acid as eluent. The concentration of the radiolabelled peptide was estimated by UV monitoring. The acylating photoactivable radioiodinated reagent N-hydroxysuccinimidyl-N-(4-azido-2-nitrophenyl)-3-[125I]iodotyrosi ne was synthesized, purified on a C18 HPLC column by isocratic elution with 65% acetonitrile-1 mM hydrochloric acid, then conjugated with (Thr 34, NLeu 37) CCK31-39. The resulting photoactivable radioiodinated CCK analogue was purified by isocratic elution on a C18 HPLC column with 39% aqueous acetonitrile-0.1 M triethylamine phosphate (pH 3.5). The binding ability of both tracers and their non-radioactive analogues to CCK receptors was tested on rat pancreatic plasma membranes. As compared to a KD of 4.5 nM for unmodified (Thr 34, NLeu 37) CCK31-39, the KD of the radioiodinated Bolton-Hunter derivative was 3 nM, and that of the photoactivable radioiodinated derivative was 19 nM.

Animals↗
PubMed2002

Determination of electroosmotic flow mobility with a pressure-mediated dual-ion technique for capillary electrophoresis with conductivity detection using organic solvents.

A method is described for the indirect determination of the mobility of the electroosmotic flow (EOF), which can be carried out within a few minutes even for very low mobilities. It is independent of the direction of the EOF. It is based on the comparison of the measured mobilities of two oppositely charged reference ions (tetraphenylphosphonium and tetraphenylborate) with given mobilities in different organic solvents (methanol, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, propylene carbonate) at ionic strengths between 5 and 50 mM. The method is based on the sequential movement of the reference ions in a three-step process: first by a laminar flow to a certain position in the separation capillary, followed by electromigration due to application of voltage, and pressurised migration towards the detector. In this way the total mobilities of the reference ions can be determined from their residence times, and the difference to their known actual mobilities gives the mobility of the EOF. The method avoids misinterpretations caused by system- and eigen-peaks, which often bias the results especially when a conductivity detector is used. The method is suitable for all solvents, and is an advantage especially for organic and mixed aqueous-organic background electrolytes with high UV absorbance.

Electric Conductivity↗
PubMed2002

Determination of alkylphosphonic acids using micellar electrokinetic chromatography with laser-induced fluorescence detection and high-salt stacking.

Methyl-, ethyl- and propylphosphonic acids (MPA, EPA, and PPA, respectively) were derivatized with panacyl bromide in dry N,N-dimethylformamide (DMF). After mixing with a high-salt dilution buffer, the derivatives were separated by micellar electrokinetic chromatography in 35 min and detected by laser-induced fluorescence (He-Cd laser excitation at 325 nm and detection at 500 nm). Baseline resolution was achieved using a separation buffer containing 50 mM sodium cholate, 40% (v/v) of acetonitrile and 50 mM borate. Addition of 400 mM NaCl to the dilution buffer allowed the injection time to be increased to 30 s while still maintaining baseline resolution. Limits of detection for MPA, EPA, and PPA were 0.13 microM (12 ppb), 0.13 microM (14 ppb) and 0.14 microM (17 ppb) injected, respectively. The reproducibility of corrected peak area at 15 microM was 3.7 approximately 4.3%.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2002

Cyanogen bromide activation and coupling of ligands to diol-containing silica for high-performance affinity chromatography optimization of conditions.

To obtain silica supports for high-performance affinity chromatography, a method of preparing CNBr-activated diol-silica under anhydrous conditions was developed. Activation of the silane-derived hydroxyls with cyanogen bromide and triethylamine was optimized and demonstrated to efficiently couple several amino ligands (tryptophan, 6-aminohexyl-Cibacron Blue, and DNA). Sonication and vacuum degassing, a procedure used to remove air from the silica beads, increased activation. Coupling of an amino ligand under slightly basic conditions (pH 8.0) gave the highest yield. The linkage between the immobilized ligands and silica was stable from pH 2-10. Anhydrous acetone was the most effective solvent for activation but dimethylformamide and 2-propanol were also good choices. The high-performance affinity chromatography columns obtained by coupling sequence-specific DNA binding sequences for Lac repressor-beta-galactosidase fusion protein were compared to affinity columns obtained by coupling the same DNA element to Sepharose beads; 5 microm silica gave the best performance.

Base Sequence↗
PubMed2003

Elution behavior of polyethylene in polar mobile phases on a non-polar sorbent.

Linear polyethylene standards in the range of 1-500 kg/mol, dissolved in 1,2,4-trichlorobenzene, were injected into a column packed with oligo(dimethylsiloxane) modified silica gel. Fifteen polar solvents (cyclohexanone, cyclohexylacetate, cyclohexanol, nonylalcohol, dimethylformamide, dimethyl sulfoxide, ethylene- and diethylene glycol monobutyl ether, benzylalcohol, hexylacetate, bis(2-ethyl-hexyl)phthalate, N,N-dimethylacetamide, propylene carbonate, dipropylene glycol and N-methyl-pyrrolidone) were evaluated as mobile phases. Depending on the type of mobile phase evaluated, different elution behaviors are observed for polyethylene: (1) polyethylene was eluted in the size exclusion mode, (2) polyethylene was eluted together with the sample solvent peak at constant elution volume, (3) polyethylene was partially or fully retained on the column. The retained polymer was easily removed from the column by injecting a small volume of trichlorobenzene. The use of ethylene glycol monobutyl ether as the mobile phase enabled separation of the polyethylene from polypropylene. In this case polypropylene is eluted in the size exclusion mode, while polyethylene is eluted at a constant elution volume or remains in the column.

Polyethylene↗
PubMed2003

Analysis of proanthocyanidins by high-performance gel permeation chromatography.

A high-performance gel permeation chromatography method was developed for the analysis of proanthocyanidins. The isocratic method consisted of two porous polystyrene-divinylbenzene columns (300 x 7.5 mm each, 5 microm, 100 and 500 A individual pore size) and a mobile phase consisting of N,N-dimethylformamide containing 1% (v/v) acetic acid, 5% (v/v) water and 0.15 M lithium chloride. The flow-rate was maintained at 1 ml/min, with a column temperature of 60 degrees C and with detection at 280 nm. The method was used to analyze proanthocyanidin fractions of increasing molecular mass and from different plant tissues. The average molecular mass of proanthocyanidin fractions as determined by acid catalysis in the presence of phloroglucinol, related well with their gel permeation chromatography column retention, yet significant differences in the retention properties between individual plant tissue isolates existed. Proanthocyanidin compositional differences between isolates may explain these differences. A second-order calibration curve was generated from fractionated grape seed proanthocyanidins and this curve was used to analyze grape seed proanthocyanidins isolated from grapes harvested at extremes of maturity.

Chromatography, Gel↗
PubMed2003

Determination of fluorinated surfactants and their metabolites in sewage sludge samples by liquid chromatography with mass spectrometry and tandem mass spectrometry after pressurised liquid extraction and separation on fluorine-modified reversed-phase sorbents.

An analytical method was elaborated for simultaneous extraction and determination of fluorinated anionic and non-ionic surfactants in sewage sludge. Surfactant compounds were determined by liquid chromatography-mass spectrometry (LC-MS) after Soxhlet extraction, hot steam extraction and pressurised liquid extraction (PLE) using spiked sludge samples. PLE in a multiple-step procedure consisting of sequential use of ethyl acetate-dimethylformamide and methanol-phosphoric acid resulted in the most efficient extraction procedure. Quantitative analyses of the fluorinated anionic perfluorooctanesulfonate (PFOS) and the partly fluorinated non-ionic alkylpolyglycol ether (FAEO) surfactants were performed by selected ion monitoring LC-MS. Electrospray ionisation or atmospheric pressure chemical ionisation in negative or positive mode was performed. Recoveries between 105 and 120% could be reached. No PFOS and non-ionic FAEO surfactants in concentrations higher than 6 or 10 mg kg(-1) dry matter were observed in real environmental samples. Therefore aerobic and anaerobic biodegradation was performed to investigate the fate of fluorinated surfactants reaching wastewaters. Biological wastewater treatment in laboratory scale under aerobic or anaerobic conditions led to an elimination by biodegradation.

Chromatography, Gas↗
PubMed2003

Novel stepwise gradient reversed-phase liquid chromatography separations of humic substances, air particulate humic-like substances and lignins.

RP-HPLC using stepwise gradients of dimethylformamide (DMF) in buffered aqueous mobile phase and a wide-pore (30 nm) octadecylsilica column has been applied to the analysis of soil, peat and air particulate humic and humic-like substances (HSs), as well as lignin, in order to demonstrate the usefulness of the approach for their characterization even at trace concentration level. Tandem combination of spectrophotometric (DAD) and fluorimetric detection was used to get more detailed information on chromatographic behaviour of HSs. The results showed that ten-step gradient can induce distinct features of HSs and lignins. Combination of very good DMF solvating and disaggregating properties for HSs and lignins together with wide pore RP sorbent improves surface interactions of the analytes and suppresses influence of size exclusion effects. Thus it provides reproducibility of characterisation profiles and robustness of the method. Very good reproducibility of retention times (from +/-0.12 to +/-0.36% RSD), of peaks enforced by the step gradient shape supports well defined characterization and/or fractionation of HSs. Evaluated limit of quantitation (S/N = 10) of selected soil humic acid working standard using fluorimetric detection (ex.470 nm/em.530 nm) was 9.7 microg/ml. This corresponds to 0.5 microg of the humic acid per injection. Calculated limit of detection (S/N = 3) was 3.3 microg/ml, what corresponds to 0.15 microg of the humic acid per injection and enabled determination of 0.1% (m/m) humic-like substances in 20 mg of air particulates under defined rules and conditions.

Air↗
PubMed1999

Highly alkaline electrolyte for single-stranded DNA separations by electrophoresis in bare silica capillaries.

A new, highly denaturing electrolyte system based on a solution containing 0.01 M NaOH, 0.0015 M Na2B4O5(OH)4 and a replaceable polymer sieving medium was designed for the separation of single-stranded DNA fragments in bare fused-silica capillaries. Extreme denaturing power, together with the optimized composition of the electrolyte, allows for a separation efficiency as high as 2,300,000 height equivalents to a theoretical plate per meter. Sample denaturation in alkaline solutions provides single-stranded DNA fragments without any intra- or intermolecular interactions at room temperature. Their electrophoretic mobilities were found to be twice those of fragments denatured by dimethylformamide or HCl. This can be interpreted in terms of an increased effective charge on the DNA molecules. The surprisingly weak electroosmosis (6 x 10(-10) m2 V-1 s-1) of polymer solutions at pH 12 or higher is considered to be the result of the dissolution of the silica capillary wall. A highly viscous thin layer of dissolved silica probably causes a shift of the slipping plane further away from the wall to the lower value of the zeta potential. Applications of the electrolyte in clinical diagnostics demonstrate its remarkable properties.

DNA, Single-Stranded↗
PubMed2000

Determination of nicarbazin and clopidol in poultry feeds by liquid chromatography.

A rapid and very effective analytical procedure for the simultaneous liquid chromatographic determination of two coccidiostats, clopidol (CLOP) and nicarbazin (NICA), in poultry feeds was developed and tested. The ground feed samples were extracted using aqueous dimethylformamide after moistening with water. Co-extracted feed constituents were removed with a solid-phase extraction alumina-basic column and the eluates were directly analyzed on an ODS column (250x4.6 mm, 5 microm) with acetonitrile-0.01 M acetate buffer (pH 4.6) as eluent. UV detection of CLOP and the 4,4'-dinitrocarbanilide portion of NICA was carried out at 265 and 345 nm, respectively. The mean recovery from NICA spiked samples was 95% with a RSD of 4% in a concentration range of 2-150 mg/kg while for CLOP it was 98% with a RSD of 5% in a concentration range of 5-150 mg/kg. The limits of detection of NICA and CLOP in feed, based on a detector signal-to-noise ratio of 3, were estimated to be 1 mg/kg and 2.5 mg/kg, respectively, and the lowest levels tested in feeds by this procedure were 2 mg/kg and 5 mg/kg, respectively.

Animal Feed↗
PubMed2003

Tubular microstructures made from nonchiral single-chain fluorinated amphiphiles: impact of the structure of the hydrophobic chain on the rolling-up of bilayer membrane.

The nonchiral, single-chain fluorinated amphiphiles derived from dimorpholinophosphate, C(n)F(2n+1)(CH(2))(m)OP(O)[N(CH(2)CH(2))(2)O](2) (FnCmDMPs), form hollow tubular bilayer-based self-assemblies when dispersed in water, ethanol/water mixtures, and dimethylformamide. The fluorinated tubules are highly stable and sturdy. Upon heating, they transform reversibly into giant multilamellar vesicles. Uncommon U-shaped and V-shaped coiled membranes were obtained from mixtures of FnCmDMPs. Depending on conditions, fluorinated tubules can evolve with time into collapsed flattened crystallized needles. The successive steps involved in the formation and evolution of these tubules were identified, and the specific features of fluorinated chains that are relevant to membrane coiling and tubule formation are discussed.

Fluorine↗