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At least 703 records · Page 39Linked to original sources
PubMed2001

Liquid chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry determination of N-methylpyrrolidinone in riverine biofilms.

A rugged procedure utilizing reversed-phase liquid chromatography with positive-ion electrospray ionization mass spectrometry (LC-MS) along with tandem MS is described for the quantification and confirmation of N-methylpyrrolidinone (NMP) in methanolic extracts of riverine biofilm. The LC-MS method provided a 100-fold improvement in detection limits (2 ng g(-1) with a repeatability of 80-95% based on triplicate analyses) compared to a conventional LC-UV detection procedure and was applicable to quantitative analysis of biofilm samples with little or no clean up. Under low-energy collision induced dissociation (CID) conditions (17 V, laboratory frame of reference, with argon as the collision gas), two product-ions of the [M+H]+ ion were formed at m/z 69 [MH-CH3NH2]+ and m/z 58 [MH-CH3NCH]+ with relative abundances of 30% and 5%, respectively. These CID transitions were used to demonstrate that biofilm uptake of a photocatalytically-generated mixture of NMP was rapid once acclimation was achieved.

Biofilms↗
PubMed2001

Analysis of the band profiles of the enantiomers of phenylglycine in liquid chromatography on bonded teicoplanin columns using the stochastic theory of chromatography.

The retention behaviour of the enantiomers of underivatized phenylglycine was studied on a Chirobiotic T column packed with amphoteric glycopeptide teicoplanin covalently bonded to the surface of silica gel. The retention and the selectivity of separation of the enantiomers increase with rising concentration of ethanol or of methanol in aqueous-organic mobile phases. The band profiles of the less retained L-phenylglycine are symmetrical, but the band profiles of the more strongly retained D-phenylglycine are tailing in all mobile phases tested. The band broadening does not diminish even at very low concentrations of phenylglycine, so that it cannot be attributed to possible column overload. The analysis of the band profile using the stochastic theory of chromatography suggests that the broadening can be attributed to at least two additional chiral centres of adsorption in the stationary phase contributing to the retention of the more strongly retained enantiomer in addition to the adsorption of the less retained one. This behaviour can be explained by the complex structure of the teicoplanin chiral stationary phase.

Adsorption↗
PubMed2001

Determination of microcystins in blue-green algae, fish and water using liquid chromatography with ultraviolet detection after sample clean-up employing immunoaffinity chromatography.

Anti-microcystin LR immunnoaffinity cartridges were evaluated for their ability to selectively remove microcystins from extracts of blue-green algae, fish and water samples for subsequent analysis by liquid chromatography with UV absorbance detection at 238 nm. Blue-green algae and fish samples were extracted with 75% methanol in water. A portion of the extract was diluted and passed through an immunoaffinity cartridge. Water samples were applied directly to the cartridge. The cartridge was rinsed with water and 25% methanol in water. The microcystins were eluted with 80% methanol in water containing 4% acetic acid. It was found that the cartridges were effective in isolating the microcystins from blue-green algae, fish and water samples, resulting in extracts that were clean enough to enable direct LC-UV detection down to approximately 0.03 microg/g in the blue-green algae and fish samples, and as low as 0.02 ng/ml for water samples. The cartridges were found to have a capacity of approximately 200 ng each for a mixture of microcystins RR, YR, LR and LA, or as much as 525-800 ng for individual compounds. Recoveries trough the complete analytical procedure ranged from 64 to 115% (all values) with an overall average of approximately 80% at spiking levels of 0.5-4.0 microg/g for the microcystins in blue-green algae. The average recoveries (n=8) from spiked (0.1-0.5 microg/g) fish samples were 73% for RR, 79% for YR, 81% for LR and 77% for LA, while from the spiked (2.0-0.04 ng/g) tap and river water samples (n=6), recoveries were 78% for RR, 86% for YR, 94% for LR and 89% for LA.

Animals↗
PubMed2001

Computer simulation of ion chromatography separation: an algorithm enabling continuous monitoring of anion distribution on an ion-exchange chromatography column.

A computer algorithm for the calculation of ion chromatography separation is presented. It is based on the calculation of equilibrium concentrations of present analyte in discrete column segments. The continuous column is treated as a number of discrete cells or segments where the equilibration process between the stationary phase and the eluent is simulated. The ion-exchange equilibration process is supposed to be instantaneous and quantitative. The continuous flow of the eluent is rendered by discrete transfers. The size of each transfer of the eluent corresponds to a portion of the volume contained in one column segment. The equilibrium calculations in all column segments are repeated for each transfer of the eluent, through all the stages of the chromatographic process. The distribution of the analytes between the stationary phase and the eluent can be monitored at any step and in any column segment which means that the described algorithm provides the spatial and time concentration profiles. The simulated chromatogram is acquired as a time-concentration profile in the last column segment. The obtained chromatograms are in good agreement with the experimental ones. The distribution of ions between the stationary phase and the eluent in the early stages of the ion chromatographic process can thus be studied with confidence.

Algorithms↗
PubMed2001

Longitudinal diffusion in size-exclusion chromatography: a stop-flow size-exclusion chromatography study.

Band broadening in size-exclusion chromatography (SEC) has an adverse effect upon calculated molecular mass averages, distributions, and dilute solution data generated using single- and multi-detector systems. In the past, the longitudinal diffusion contribution to band broadening in SEC has been considered negligible. This assumption has been investigated by using a stop-flow methodology (SF-SEC) that maximizes the potential for longitudinal diffusion while minimizing that for mass transfer. Under the given experimental conditions, the effects of B-term band broadening were manifest only below 30 KDa, irrespective of chemical functionality or molecular mass polydispersity. This type of broadening was found to be flow rate-independent for a representative high molecular mass polymer.

Chromatography, Gel↗
PubMed2002

Solute-solvent interactions in micellar electrokinetic chromatography. III. Characterization of the selectivity of micellar electrokinetic chromatography systems.

Several micellar electrokinetic chromatography (MEKC) systems (sodium dodecyl sulfate, lithium dodecyl sulfate, lithium perfluorooctanesulfonate, sodium cholate, sodium deoxycholate, tetradecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide) have been characterized by means of the solvation parameter model. It has been observed that the coefficients of the correlation equations depend strongly on the particular set of compounds analyzed. Principal component analysis has been used to characterize the 2975 compounds with available solute descriptors and to select an appropriate subset of compounds to be analyzed by MEKC. With this set of compounds, the MEKC systems have been characterized. Principal component analysis has also been used to show the similarities and differences between the properties of the surfactants characterized by MEKC.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2002

Trace determination of priority pesticides in water by means of high-speed on-line solid-phase extraction-liquid chromatography-tandem mass spectrometry using turbulent-flow chromatography columns for enrichment and a short monolithic column for fast liquid chromatographic separation.

An integrated on-line SPE-HPLC-MS/MS system has been developed for the rapid analysis of various trace level priority pesticides in surface and drinking water. Eleven pesticides were included in this study, with various phenylureas, triazines and organophosphorous species among them. Use of turbulent-flow chromatography columns (TFC, 50 x 1 mm, 30-50 microm particle size) as extraction cartridges enables fast on-line SPE at high sampling flow-rate (5 ml/min). Polymeric and carbon based TFC columns (Oasis HLB, Cyclone, Hypercarb) allow complete extraction with good recoveries from water volumes up to 50 ml. On-line coupling to HPLC is performed with re-mixing of the organic TFC eluate with water in front of the analytical column to ensure efficient band focussing. For fast HPLC analysis, a short monolithic column is applied in combination with highly selective API-MS/MS detection. Matrix effects on the APCI-MS/MS signal were found to be reduced by the system to an acceptable minimum. Limits of detection, determined for 10-ml samples of river water were in the range between 0.4 and 13 ng/l typically, except trifluralin (approximately 280 ng/l), which is less susceptible to ionization under atmospheric pressure conditions. At an enriched water volume of 10 ml, the whole SPE-HPLC-MS/MS procedure requires less than 14 min. The method was successfully applied to the analysis of drinking and surface water samples taken from several sampling sites around the city of Leipzig, Germany. Concentrations measured (maximum: 16 ng/l simazine in river water) were far below the concentration limits scheduled by law.

Chromatography, High Pressure Liquid↗
PubMed1988

Identification of trimethyllead in urine by high-performance liquid chromatography with column switching and chemical reaction detection and by liquid chromatography-mass spectrometry.

Incorporated tetraalkyllead compounds are metabolized in the liver and the highly toxic trialkyllead species are excreted via the urine. The procedure for the determination of these metabolites in urine consists of solid-phase enrichment, reversed-phase pre-column high-performance liquid chromatography (HPLC) and chemical reaction detection. As urine is a very complex matrix, it must be questioned whether the retention time alone is a sufficient criterion for the identification of the analytes. For the trimethyllead ion the validity of the results was examined by selectivity checks of the chemical reaction detector, by the application of different stationary and mobile phases in single and dual pre-column HPLC systems and by the use of thermospray LC-mass spectrometry as an independent method. The results demonstrated that the recommended method is accurate for the determination of trimethyllead in urine samples.

Chromatography, High Pressure Liquid↗
PubMed1988

High-performance liquid chromatography of proteins on compressed, non-porous agarose beads. I. Hydrophobic-interaction chromatography.

Macroporous agarose beads were converted into non-porous beads by shrinkage and cross-linking in organic solvents. These beads could be used for high-performance hydrophobic-interaction chromatography without derivatization with non-polar ligands, because the 1,4-butanediol diglycidyl ether, used as cross-linker, gives relatively hydrophobic bridges. The resolution for compressed columns packed with these beads was determined as a function of gradient time at constant flow-rate, flow-rate at constant gradient volume and flow-rate at constant gradient time and as a function of loading capacity. Interestingly, the resolution is virtually independent of flow-rate at constant gradient volume even when the column is packed with relatively large beads (diameter 30 microns). The beads have the advantage of being stable up to pH 14.

Butylene Glycols↗
PubMed1987

High-performance liquid chromatography of amino acids, peptides and proteins. LXXIII. Investigations on the relationships between molecular structure, retention and band-broadening properties of polypeptides separated by reversed-phase high-performance liquid chromatography.

The gradient retention behaviour in reversed-phase high-performance liquid chromatography of a series of polypeptides related to human beta-endorphin has been investigated using different n-alkylsilica stationary phases and 0.1% trifluoroacetic acid in water-acetonitrile as mobile phase. In particular, the influence of changes in gradient time and flow-rate on retention parameters has been assessed with five different porous octadecylsilica phases with average particle diameters of 4 microns and 6 microns. Decreasing the pore size from 30 nm to 7.3 nm resulted in decreased S and log k'o values for most solutes. The effect of changes in the gradient steepness parameter, b, on the bandwidth behaviour of these polypeptides has also been investigated. Anomalous band-broadening was observed for very steep and very shallow gradients, i.e. b greater than 0.7 or b less than 0.2. The significance of these results is discussed in relation to the presence of hydrophobic domains in the linear sequence, the probability of the formation of highly stabilised secondary structures and the possible involvement of multiple folded forms of a single solute in the chromatographic performance of these polypeptides.

Amino Acids↗
PubMed1987

Evaluation of advanced silica packings for the separation of biopolymers by high-performance liquid chromatography. V. Performance of non-porous monodisperse 1.5-microns bonded silicas in the separation of proteins by hydrophobic-interaction chromatography.

Non-porous monodisperse 1.5-microns silicas were allowed to react with (A) and (B) N-acetylaminopropyltriethoxysilane to generate bonded phases useful in high-performance hydrophobic-interaction chromatography (HIC). Differences in the selectivity were observed between the amide and the ether phase. Peak capacities between 10 and 30 were achieved for several proteins with the amide and ether phase packed into columns of 36 X 8 mm I.D. and elution of the proteins under chromatographic conditions in which the gradient volume, VG, was held constant by varying the gradient time between 20 and 2.5 min and the flow-rate between 0.5 and 4.0 ml/min. The S values derived from the dependences of log k' on the volume fraction of the low ionic strength buffer, phi b, were of the same magnitude as reported for porous HIC silicas and showed a dependence on the molecular weight of the protein. Using these HIC stationary phases based on non-porous 1.5-microns supports, fast separations (less than 5 min) could be carried out with high biological recoveries.

Ammonium Sulfate↗
PubMed1987

High-performance liquid chromatography of amino acids, peptides and proteins. LXXIV. Separation of heparin-binding growth factors by reversed-phase high-performance liquid chromatography.

The separation of several immunologically related forms of the bovine brain basic heparin-binding growth factor by reversed-phase high-performance liquid chromatography is described. With Bakerbond C4 reversed-phase columns, it is possible to resolve the 0.8-1.0 M sodium chloride and the 1.0-1.3 M sodium chloride components from the preceding heparin-Sepharose affinity chromatographic step in the purification procedure for these polypeptide mitogens into multiple active forms, all of which exhibit similar molecular weights and immunoreactivity with specific polyclonal antisera. Structural characterisation suggests that it is likely that these forms represent different stages in the post-translational processing of these polypeptide mitogens.

Amino Acids↗
PubMed1990

High-performance liquid chromatography of transfer ribonucleic acids on spherical hydroxyapatite beads. II. Effects of pH and sodium chloride on chromatography.

The effects of pH and sodium chloride on the high-performance liquid chromatography of transfer ribonucleic acids (tRNAs) on spherical hydroxyapatite beads were investigated. Binding of tRNAs on the beads was strengthened by increasing the pH of the mobile phase (phosphate buffer, pH 6.4-8.0), a phenomenon which is opposite to the retention of proteins on the beads. By using phosphate buffer of pH 8.0 instead of pH 6.8, the resolution of tRNAs was improved significantly; as many as ten times more theoretical plates were calculated with the use of the former buffer. Addition of sodium chloride to the phosphate buffer has a bifunctional effect on the retention of tRNAs: elution of tRNA(f-Met) and tRNA(Val) was retarded whereas that of tRNA(Phe) was facilitated.

Bacillus subtilis↗
PubMed1989

Centrifugal counter-current partition chromatography with helical coil rotor. Simplified counter-current chromatography with a rotating face-seal.

A centrifugal counter-current partition chromatograph has been developed and tested in order to simplify earlier counter-current chromatographic (CCC) procedures. It includes a helical coil rotor and a rotating face-seal. The rotor is designed to be adapted in an ordinary laboratory centrifuge for toroidal coil CCC. Twisting between the inlet and outlet tubing is avoided by using the rotating seal in the rotor. The seal is placed between the rotor, on which helical coils are mounted, and a newly designed centrifuge lid. This chromatographic rotor, rotating simply around its own axis, has simplified a previous CCC device in which a coil planet mechanism is used to avoid tube twisting whilst retaining the capability for chromatographic separations. Results for separations of nystatin, dinitrophenylamino acids and Poly I:C were comparable to those obtained by liquid chromatography and the previous CCC procedure.

Amino Acids↗
PubMed1989

High-performance liquid chromatography of amino acids, peptides and proteins. XC. Investigations into the relationship between structure and reversed-phase high-performance liquid chromatography retention behaviour of peptides related to human growth hormone.

The gradient elution behaviour of eight synthetic peptides encompassing residues [6-13] of human growth hormone, i.e. Leu1-Ser-Arg-Leu-Phe-Asp-Asn-Ala8, has been investigated, by using an octadecylsilica, a butylsilica, and a polymeric fluorocarbon as stationary phases. Quantitative expressions, derived from the linear-solvent-strength theory and the general plate-height theory, were used to assess the influence of gradient time on the relative retention and bandwidths of these peptides. It was demonstrated that the chromatographic properties of the cyclised imide form involving Asp6 are consistent with the formation of a highly stabilised amphipathic helix, while the open-chain alpha- and beta-rearranged forms eluted as less rigid structures. The putative hydrophobic contact region consists of two leucine residues and one phenylalanine residue. From an analysis of the retention and bandwidth data obtained at pH 9, a surface-induced molecular reorientation of the beta-linked peptides was observed, in which the repulsion of the aspartyl carboxyl group from the hydrophobic stationary phase directs the C-terminal moiety away from the sorbent surface. Furthermore, the fluorocarbon sorbent exhibited characteristics favourable for use in preparative purification of these peptides. The present results demonstrate the sensitivity of reversed-phase high-performance liquid chromatography (RP-HPLC) to monitor small changes in the interactive behaviour of peptides with hydrocarbonaceous ligands and aquo-organic solvent combinations in reversed-phase systems. These observations further illustrate the general utility of HPLC for investigating the conformational behaviour of peptides at solid-liquid interfaces.

Amino Acids↗
PubMed1989

Application of thermospray liquid chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry for the identification of cynomolgus monkey and human metabolites of SK & F 101468, a dopamine D2 receptor agonist.

A combination of thermospray liquid chromatography-mass spectrometry (LC-MS) and LC MS MS has allowed the structural elucidation of a number of metabolites of 4-[2-(dipropylamino)ethyl]-1,3-dihydro-2H-indol-2-one (SK & F 101468) in monkey urine. By using LC-MS-MS with the third quadrupole (Q3) set up in multiple ion detection (MID) mode, a number of metabolites were subsequently detected in the human urine and plasma samples despite very low dosing regimes. This was achieved with minimal sample preparation, e.g. for the urine sample centrifugation was the only preparative step, in order to remove particulate matter, prior to analysis. The good signal-to-noise ratio obtained for the human samples, using LC MS MS with Q3 set up for MID, raised the possibility of a LC-MS-MS quantitative assay. As a result, the detection limit of this method for SK&F 101468 when dissolved in methanol was determined to be in the region of 20 pg on column.

Animals↗
PubMed1989

Size-exclusion chromatography of DNA restriction fragments. Fragment length determinations and a comparison with the behaviour of proteins in size-exclusion chromatography.

Size-exclusion chromatography of double-stranded DNA restriction fragments on Superose 6 is shown to be an accurate method for chain length determination of unknown DNA. Ionic interaction was observed between DNA and the gel matrix but was easily prevented by the addition of 0.15-0.2 M sodium chloride to the eluent. Compared to protein, the selectivity curve of DNA fragments was found to be steeper reflecting the different chromatographic behaviour of rod-like and globular molecules. The relationships between the selectivity curves of DNA and protein were similar on Superose 6 and on Sephacryl S-500.

Chromatography, Gel↗
PubMed1987

Chromatography of progesterone and its major metabolites in rat plasma using microbore high-performance liquid chromatography columns with conventional injection and detection systems.

A separation of progesterone and its metabolites 17 alpha-hydroxyprogesterone, 20 alpha-hydroxy-4-pregnen-3-one, androstenedione and testosterone by high-performance liquid chromatography with a ternary solvent system is demonstrated. It is found that using a 100 X 1 mm microbore column, higher sensitivity is obtained in the ultraviolet detection of these compounds by using conventionally sized flow cells despite the higher efficiency resulting from the use of a micro-flow cell. It is also shown that, when a non-eluting solvent is used for injection, large injection volumes do not reduce column efficiency, and a 14-fold increase in sensitivity is obtained with a 1-mm column in place of one 4.6 mm in diameter. Using solid-phase extraction and concentration of the sample as pretreatment, progesterone and its hydroxylated metabolites are determined in 0.5-ml samples of rat plasma. The progesterone levels are compared with those obtained by radioimmunoassay.

17-alpha-Hydroxyprogesterone↗