Home About us Contact
|
Home About us Contact | ||
|
|
||
Peak Shape (peak + shape)
Selected AbstractsDetermination of Lead and Cadmium at Silver Electrode by Subtractive Anodic Stripping Voltammetry in Plant Materials Containing TlELECTROANALYSIS, Issue 9 2005Beata Krasnod, bska-Ostr Abstract Lead and cadmium have been determined by the subtractive anodic stripping voltammetry using the square-wave mode at a silver electrode without removal of oxygen. The samples containing large amount of thallium were collected from a highly contaminated region. The presence of thallium strongly affects the peak shape of Cd. The plant material digestion was performed with HNO3/HClO4 mixture using pressurised microwave decomposition. The proposed method used for the lead determination was validated by the inter-method comparison (ICP-MS). The cadmium determination was validated using certified reference material. The results obtained, supported by statistical tests, demonstrated the usefulness of the method for the lead determination in samples containing large amounts of Cd and Tl. It is important to note that Cd can only be quantified when the thallium concentration is much lower than that of cadmium. [source] Microchip isoelectric focusing with monolithic immobilized pH gradient materials for proteins separationELECTROPHORESIS, Issue 23 2009Yu Liang Abstract Monolithic immobilized pH gradient (M-IPG) materials were prepared in microchannles by photoinitiated polymerization of acrylamide, glycidylmethacrylate and Bis, followed by the attachment of focused Ampholine onto the surface of porous monoliths via epoxide groups. With M-IPG materials as matrix, FITC-labeled ribonuclease B, myoglobin and ,-casein were well separated by microchip isoelectric focusing (,CIEF) without carrier amphocytes (CAs) added in the buffer. Both chemical and pressure mobilization were applied to drive focused zones for LIF detection. Our experimental results showed that pressure mobilization was preferable with neglectable band broadening, and good peak shape and high detection sensitivity were obtained. All these results demonstrate that ,CIEF with M-IPG materials is not only an efficient mode for protein enrichment and separation but also attractive to couple with other CE modes to achieve multi-dimensional separation or MS for further identification, without the interference of mobile CAs. [source] CE-MS method development for peptides analysis, especially hepcidin, an iron metabolism markerELECTROPHORESIS, Issue 15 2009Gaëlle B. Martin Abstract A method for the resolution of a peptides mixture including hepcidin-25, an iron metabolism marker, was developed by CE-ESI-MS. Several strategies were tested to optimize peptide separation, such as the addition of cyclodextrins or organic solvents in the BGE or the use of coated capillaries. Best results in terms of resolution, symmetry and efficiency were obtained with a BGE made of 500,mM ammonium acetate pH 4.5/ACN 70:30,v/v. Using the methodology of experimental design, BGE concentration, sheath liquid composition and MS-coupling parameters were then optimized in order to obtain the best signal intensity for hepcidin. Finally, a 225,mM BGE and a sheath liquid composed of isopropanol/water 80:20,v/v containing 0.5%,v/v formic acid were selected as it constitutes the best compromise for selectivity, peak shape and sensitivity. [source] Co-electroosmotic capillary electrophoresis of basic proteins with 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids as non-covalent coating agents of the fused-silica capillary and additives of the electrolyte solutionELECTROPHORESIS, Issue 11 2009Danilo Corradini Abstract The paper reports the results of a study carried out to evaluate the use of three 1-alkyl-3-methylimidazolium-based ionic liquids as non-covalent coating agents for bare fused-silica capillaries and additives of the electrolyte solutions (BGE) for CE of basic proteins in the co-EOF separation mode. The three ionic liquids are differentiated from each other by the length of the alkyl group on the imidazolium cation, consisting of either an ethyl, butyl or octyl substituent, whereas tetrafluoroborate is the common anionic component of the ionic liquids. Coating the capillary with the ionic liquid resulted in improved peak shape and protein separation, while the EOF was maintained cathodic. This indicates that each ionic liquid is effective at masking the protein interaction sites on the inner surface of the capillary, also when its adsorption onto the capillary wall has not completely neutralized all the negative charges arising from the ionization of the silanol groups and the ionic liquid is not incorporated into the BGE employed for separation. Using the coated capillaries with BGE containing the ionic liquid employed for the coating, at concentration low enough to maintaining the EOF cathodic, both peak shape and protein separation varied to different extents, based on the particular ionic liquid used and its concentration. Fast and efficient separation of the model basic protein mixture in co-electroosmotic CE is obtained with the 1-butyl-3-methylimidazolium tetrafluoroborate coated capillary and 100,mM acetate buffer (pH 4.0) containing 4.4,mM 1-butyl-3-methylimidazolium tetrafluoroborate as the BGE. [source] Retention of proteins and metalloproteins in open tubular capillary electrochromatography with etched chemically modified columns,ELECTROPHORESIS, Issue 18 2008Joseph J. Pesek Abstract Etched chemically modified capillaries with two different bonded groups (pentyl and octadecyl) are compared for their migration behavior of several common proteins and metalloproteins as well as metalloproteinases. Migration times, efficiency and peak shape are evaluated over the pH range of 2.1,8.1 to determine any effects of the bonded group on the electrochromatographic behavior of these compounds. One goal was to determine if the relative hydrophobicity of the stationary phase has a significant effect on proteins in the open tubular format of capillary electrochromatography as it does in HPLC. Reproducibility of the migration times is also investigated. [source] Rapid capillary electrophoresis time-of-flight mass spectrometry separations of peptides and proteins using a monoquaternarized piperazine compound (M7C4I) for capillary coatingsELECTROPHORESIS, Issue 8 2008Anisa Elhamili Abstract A monoquaternarized piperazine, 1-(4-iodobutyl) 4-aza-1-azoniabicyclo[2,2,2] octane iodide (M7C4I), has been evaluated as a surface derivatization reagent for CE in combination with TOF MS for the analysis of proteins, peptides, and protein digests. The M7C4I piperazine, at alkaline pH, forms a covalent bond via alkylation of the ionized silanols producing a cationic surface with a highly stable and reversed EOF. The obtained surface yields rapid separations (less than 5,min) of peptides and proteins at acidic pH with high separation efficiencies (up to 1.1×106 plates/m for peptides and up to 1.8×106 plates/m for proteins) and no observed bleeding of the coating reagent into the mass spectrometer. The simplicity of the coating procedure also enables fast (2,min) regeneration of the surface, if necessary. This is useful in the analysis of complex samples in order to prevent possible memory effects. The potential of using M7C4I-coated capillaries for MS analysis of complex samples is demonstrated by the separation of peptides, proteins, and protein digests. Even more, the spectacular thing in which large intact proteins with molecular masses over 0.5,MDa could be separated. The coating showed good ability to handle these large proteins with high efficiency and retained peak shape as demonstrated by separation of IgG1 (150,kDa) and thyroglobulin (669,kDa). [source] Enhanced pH-mediated stacking of anions for CE incorporating a dynamic pH junctionELECTROPHORESIS, Issue 20 2007Stacy D. Arnett Abstract A technique has been developed to enhance analyte focusing for CE for the analysis of physiological samples. High-ionic-strength samples are titrated to low-ionic-strength on-line using pH-mediated sample stacking in conjunction with a dynamic pH junction. This method concentrates analytes by reducing their electrophoretic mobility during field-amplification. Parameters responsible for enhanced focusing were investigated, and an enhanced pH-mediated stacking method was optimized for anionic nucleosides. The process results in ultra-narrow peak widths, for example, 0.28,s for thymidine with a 10,min analysis time. Peak width and resolution with the enhanced stacking method were also compared to normal base stacking and electrokinetic injection. With this technique, mass-loading capacity can be increased without degradation in peak shape and resolution is dramatically improved. [source] Chiral CE of aromatic amino acids by ligand-exchange with zinc(II),L -lysine complexELECTROPHORESIS, Issue 15 2007Li Qi Abstract A novel method of chiral ligand-exchange CE was developed with either L - or D -lysine (Lys) as a chiral ligand and zinc(II) as a central ion. This type of chiral complexes was explored for the first time to efficiently separate either individual pairs of or mixed aromatic amino acid enantiomers. Using a running buffer of 5,mM ammonium acetate, 100,mM boric acid, 3,mM ZnSO4·7H2O and 6,mM L -Lys at pH,7.6, unlabeled D,L -tryptophan, D,L -phenylalanine, and D,L -tyrosine were well separated, giving a chiral resolution of up to 7.09. The best separation was obtained at a Lys-to-zinc ratio of 2:1, zinc concentration of 2,4,mM and running buffer pH,7.6. The buffer pH was determined to have a strong influence on resolution, while buffer composition and concentration impacted on both the resolution and peak shape. Boric acid with some ammonium acetate was an adoptable buffer system, and some additives like ethylene diamine tetraacetic acid capable of destroying the complex should be avoided. Fine-tuning of the chiral resolution and elution order was achieved by regulating the ratio of L -Lys to D -Lys; i.e. the resolution increased from zero to its highest value as the ratio ascended from 1:0 to 1:infinitive, and L -isomers eluted before or after D -isomers in excessive D - or L -Lys, respectively. [source] Preparative capillary zone electrophoresis using a dynamic coated wide-bore capillaryELECTROPHORESIS, Issue 15 2006Mahmoud M. Yassine Abstract Preparative capillary zone electrophoresis separations of cytochrome,c from bovine and horse heart are performed efficiently in a surfactant-coated capillary. The surfactant, dimethylditetradecylammonium bromide (2C14DAB), effectively eliminated protein adsorption from the capillary surface, such that symmetrical peaks with efficiencies of 0.7,million plates/m were observed in 50-µm,id capillaries when low concentrations of protein were injected. At protein concentrations greater than 1,g/L, electromigration dispersion became the dominant source of band broadening and the peak shape distorted to triangular fronting. Matching of the mobility of the buffer co-ion to that of the cytochrome,c resulted in dramatic improvements in the efficiency and peak shape. Using 100,mM bis(2-hydroxyethyl)imino-tris(hydroxymethyl)methane phosphate buffer at pH,7.0 with a 100-µm,id capillary, the maximum sample loading capacity in a single run was 160,pmol (2.0,µg) of each protein. [source] Hyperspectral NIR image regression part II: dataset preprocessing diagnosticsJOURNAL OF CHEMOMETRICS, Issue 3-4 2006James Burger Abstract When known reference values such as concentrations are available, the spectra from near infrared (NIR) hyperspectral images can be used for building regression models. The sets of spectra must be corrected for errors, transformed to reflectance or absorbance values, and trimmed of bad pixel outliers in order to build robust models and minimize prediction errors. Calibration models can be computed from small (<100) sets of spectra, where each spectrum summarizes an individual image or spatial region of interest (ROI), and used to predict large (>20,000) test sets of spectra. When the distributions of these large populations of predicted values are viewed as histograms they provide mean sample concentrations (peak centers) as well as uniformity (peak widths) and purity (peak shape) information. The same predicted values can also be viewed as concentration maps or images adding spatial information to the uniformity or purity presentations. Estimates of large population statistics enable a new metric for determining the optimal number of model components, based on a combination of global bias and pooled standard deviation values computed from multiple test images or ROIs. Two example datasets are presented: an artificial mixture design of three chemicals with distinct NIR spectra and samples of different cheeses. In some cases it was found that baseline correction by taking first derivatives gave more useful prediction results by reducing optical problems. Other data pretreatments resulted in negligible changes in prediction errors, overshadowed by the variance associated with sample preparation or presentation and other physical phenomena. Copyright © 2007 John Wiley & Sons, Ltd. [source] Matrix effects on accurate mass measurements of low-molecular weight compounds using liquid chromatography-electrospray-quadrupole time-of-flight mass spectrometry,JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 3 2006F. Calbiani Abstract Liquid chromatography (LC) with high-resolution mass spectrometry (HRMS) represents a powerful technique for the identification and/or confirmation of small molecules, i.e. drugs, metabolites or contaminants, in different matrices. However, reliability of analyte identification by HRMS is being challenged by the uncertainty that affects the exact mass measurement. This parameter, characterized by accuracy and precision, is influenced by sample matrix and interferent compounds so that questions about how to develop and validate reliable LC-HRMS-based methods are being raised. Experimental approaches for studying the effects of various key factors influencing mass accuracy on low-molecular weight compounds (MW < 150 Da) when using a quadrupole-time-of-flight (QTOF) mass analyzer were described. Biogenic amines in human plasma were considered for the purpose and the effects of peak shape, ion abundance, resolution and data processing on accurate mass measurements of the analytes were evaluated. In addition, the influence of the matrix on the uncertainty associated with their identification and quantitation is discussed. A critical evaluation on the calculation of the limits of detection was carried out, considering the uncertainty associated with exact mass measurement of HRMS-based methods. The minimum concentration level of the analytes that was able to provide a statistical error lower than 5 ppm in terms of precision was 10 times higher than those calculated with S/N = 3, thus suggesting the importance of considering both components of exact mass measurement uncertainty in the evaluation of the limit of detection. Copyright © 2006 John Wiley & Sons, Ltd. [source] Mobile phase additives for enhancing the chromatographic performance of astaxanthin on nonendcapped polymeric C30 -bonded stationary phasesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 1 2009Philipp Kaiser Abstract Astaxanthin shows peak deformation and reduced peak area response when eluted with methanol and methyl tert -butyl ether on nonendcapped polymeric C30 -bonded HPLC phases. The present study tested different column manufacturers, column batches, and ten mobile phase additives including acids, bases, buffers, complexing and antioxidant agents for improvement of peak shape and peak area response. Concerning chromatographic benefits and feasibility, ammonium acetate was found to be the best additive followed by triethylamine for all columns tested. Variation of the mobile phase pH equivalent and the column temperature showed no synergistic effects on peak shape and peak area response. Results indicate that peak tailing and variation of peak area response are due to different on-column effects. Possible mechanisms of the observed phenomenon will be discussed. [source] Evaluation of mobile phase, ion pairing, and temperature influence on an HILIC-MS/MS method for L -arginine and its dimethylated derivatives detectionJOURNAL OF SEPARATION SCIENCE, JSS, Issue 13 2008Giuseppe Paglia Abstract Asymmetric NG,,NG -dimethylarginine (ADMA) increases in diseases such as renal failure, diabetes mellitus, and hypercholesterolemia. The feasibility and utility of a hydrophilic interaction chromatography (HILIC) method for the separation of free L -arginine (Arg), ADMA, and symmetric NG,,NG, -dimethylarginine (SDMA) on a typical silica column were explored and the impact of some experimental parameters on the chromatographic behavior of these analytes was investigated. The effect of water and TFA content in mobile phase and of column temperature was investigated during the development of a fast and simple HILIC-MS/MS method that might be suitable for the quantification of free Arg, ADMA, and SDMA in plasma for routine analysis. Our results show that a good compromise between efficiency and peak shape with acceptable retention and total chromatographic run time is achieved using an ACN/water (90:10) mobile phase with TFA% as additive ranging from 0.015 to 0.025% and column temperature ranging from 25 to 30°C. [source] Use of evaporative light scattering detector in the detection and quantification of enantiomeric mixtures by HPLCJOURNAL OF SEPARATION SCIENCE, JSS, Issue 10 2006Tong Zhang Abstract Routinely used in our laboratories at analytical scale, an evaporative light scattering detector (ELSD) has proved to be versatile in the detection of enantiomeric resolution using chiral stationary phases by HPLC. Though this kind of detector has been widely used in various domains, its application in enantiomeric resolution has not been discussed in the literature and is found to have very specific features especially in the quantitative perspective. In contrast with the UV detection, the peak area from ELSD for both enantiomers of a racemic mixture may not be the same. This complicates the assessment of the enantiomeric purity of unknown samples. This current work deals with some practical aspects in the detection of enantiomers and in accurate quantitative determination of enantiomeric purity by ELSD. Effects of analyte nature (more precisely molecular weight and volatility), peak shape and peak shape difference between enantiomers on the quantitative integration by ELSD are discussed in connection with the UV-detection results. The calibration for quantitative enantiomeric analysis and its effectiveness are demonstrated. [source] Optimization of the separation conditions of tetracyclines on a preselected reversed-phase column with embedded urea groupJOURNAL OF SEPARATION SCIENCE, JSS, Issue 7 2006Leila Kallel Abstract The use of a C12 stationary phase with embedded polar group has been investigated for the separation of seven tetracyclines. The influence of pH, organic modifier, buffer, and temperature on the peak shape and analyte separation was discussed. It appears that all the chromatographic conditions had a great effect on both the resolution and peak shape whereas the elution order was not affected. The baseline separation with symmetrical peaks of the seven tetracyclines can be obtained with a mobile phase containing either 5 mM phosphate buffer pH 2.5/ACN (84 : 16 v/v) or 5 mM perchlorate buffer pH 2.5/ACN (75 : 25 v/v) at a temperature not exceeding 20°C. This study reveals that the retention mechanism is ion-pairing. [source] Surface derivatization of poly(p -phenylene terephthalamide) fiber designed for novel separation and extraction mediaJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17 2005Akira Abe Abstract The surface derivatization of poly(p -phenylene terephthalamide) fiber was studied. The obtained surface-derivatized filaments were packed into a fused-silica capillary to evaluate its surface characteristics by using GC. As the stationary phase for GC the surface-derivatized fibers showed higher retention for alkanes and alkylbenzenes than that with the untreated Kevlar fiber. The improvements on the retention power and the peak shape were observed on the benzyl-modified fibrous stationary phase. The derivatized fibrous materials were also evaluated as the extraction medium in fiber-in-tube SPE, and the effect of the surface modification on the extraction power was compared to the parent fiber. The results indicated that the modified fiber possessed a higher extraction power than the untreated fiber. Based on the facts, the successful modification of the fiber surface was estimated. [source] Dislocation density assessment via X-ray GaN rocking curve scansPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010I. Booker Abstract The line shape of X-ray diffraction (XRD) rocking curves of GaN layers grown epitaxially on (0001) oriented sapphire substrates is analyzed. Measurements performed with double- and triple-crystal setup show a q -3 and q -4 intensity decay, respectively, as expected for peak broadening dominated by randomly distributed dislocations. A model developed in [2], based on a restricted random dislocation distribution is fitted to the entire peak shape and used to extract dislocation densities and correlation lengths for edge and screw type threading dislocations. Parameters extracted by double- and triple-crystal x-ray diffraction measurements agree well with each other but still must be verified by systematic cross-sectional TEM measurements. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mass peak shape improvement of a quadrupole mass filter when operating with a rectangular wave power supplyRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2009Chan Luo Numeric experiments were performed to study the first and second stability regions and find the optimal configurations of a quadrupole mass filter constructed of circular quadrupole rods with a rectangular wave power supply. The ion transmission contours were calculated using ion trajectory simulations. For the first stability region, the optimal rod set configuration and the ratio r/r0 is 1.110,1.115; for the second stability region, it is 1.128,1.130. Low-frequency direct current (DC) modulation with the parameters of m,=,0.04,0.16 and ,,=,,/,,=,1/8,1/14 improves the mass peak shape of the circular rod quadrupole mass filter at the optimal r/r0 ratio of 1.130. The amplitude modulation does not improve mass peak shape. Copyright © 2009 John Wiley & Sons, Ltd. [source] Systematic LC-MS/MS bioanalytical method development that incorporates plasma phospholipids risk avoidance, usage of incurred sample and well thought-out chromatographyBIOMEDICAL CHROMATOGRAPHY, Issue 1 2010Mohammed Jemal Abstract This treatise summarizes the underlying principle and the road map for systematic LC-MS/MS bioanalytical method development. The three themes that have recently emerged as central to building quality during method development,phospholipids, incurred sample and sound chromatographic considerations,are the main focus of this article. In order to reduce the bioanalytical risk associated with plasma phospholipids, a dual approach involving extraction and chromatography is recommended. The use of incurred sample during method development is essential to avoid interference arising from drug-related components. This is different from the current practice of incurred sample reanalysis, which tests reproducibility during method application. LC column/mobile phase optimization is needed to achieve appropriate peak shape, sensitivity and the separation of the analyte from interfering metabolites and phospholipids. Related to sound chromatographic considerations, we lay out facts and myths related to UPLC, vis-à-vis HPLC. Incorporation of quality during method development avoids the costly experience of finding out by chance about the invalidity of a method after it has been used in support of a number of pivotal clinical and non-clinical studies. To this end, we put forth an outline of a protocol for a systematic LC-MS/MS bioanalytical method development. Copyright © 2009 John Wiley & Sons, Ltd. [source] Use of capillary electrophoresis in drug quality assessment of synthetic porcine secretinBIOMEDICAL CHROMATOGRAPHY, Issue 1 2005Baile A. Moumakwa Abstract The purity pro,le for porcine secretin attributable to contamination by equilibrium products such as aspartoyl3 secretin has been shown to be dependent on the pH of the analytical system. Capillary zone electrophoresis (CZE) methods have been developed for the ef,cient separation of synthetic porcine secretin, its equilibrium products and other impurities in aqueous solutions at both acidic and alkaline pH. These conditions are more representative of those used for the reconstitution and administration of porcine secretin, and good results cannot be achieved using HPLC due to poor peak shape above pH 5.8. The in,uence of various CZE operational parameters was systematically examined. The methods were validated for accuracy, precision, linearity, LOD and LOQ. A comparative evaluation of the stability of test solutions was determined using CZE and HPLC over a range of pH values. HPLC and CZE methods produced similar results at low pH. Copyright © 2004 John Wiley & Sons, Ltd. [source] Structure, biological activity and membrane partitioning of analogs of the isoprenylated a -factor mating peptide of Saccharomyces cerevisiaeCHEMICAL BIOLOGY & DRUG DESIGN, Issue 5 2000H. Xie Abstract: Previous biochemical investigations on the Saccharomyces cerevisiaea -factor indicated that this lipopeptide pheromone [YIIKGVFWDPAC(farnesyl)OMe] might adopt a type II ,-turn at positions 4 and 5 of the peptide sequence. To test this hypothesis, we synthesized five analogs of a -factor, in which residues at positions 4 and 5 were replaced with: l -Pro4(I); d -Pro4(II); l -Pro4 - d -Ala5(III); d - Pro4 - l -Ala5(IV); or Nle4(V). Analogs were purified to > 99% homogeneity as evidenced by HPLC and TLC and were characterized by mass spectrometry and amino acid analysis. Using a growth arrest assay the conformationally restricted a -factor analogs I and III were found to be almost 50-fold more active than the diastereometric homologs II and IV and were equally active to wild-type a -factor. Replacement of Lys4 with the isosteric Nle4 almost abolished the activity of the pheromone. Thus, the incorporation of residues that promote a type II ,-turn compensated for the loss of the favorable contribution of the Lys4 side chain to pheromone activity. CD spectra on these peptides suggested that they were essentially disordered in both TFE/H2O and in the presence of DMPC vesicles. There was no correlation between CD peak shape and biological activity. Using fluorescence spectroscopy we measured the interaction of lipid vesicles with these position 4 and 5 analogs as well as with three a -factor analogs with a modified farnesyl group. The results indicated that modifications of both the peptide sequence and the lipid moiety affect partitioning into lipid, and that no correlation existed between the propensity of a pheromone to partition into the lipid and its biological activity. [source] Additive concentration effects on enantioselective separations in supercritical fluid chromatography,CHIRALITY, Issue 4 2003Karen W. Phinney Abstract Polar additive concentration effects in supercritical fluid chromatography were studied on chiral stationary phases having either a macrocyclic glycopeptide or a derivatized polysaccharide as the chiral selector. Two basic additives, isopropylamine and triethylamine, were incorporated into the methanol modifier at various concentrations and the effects on retention, selectivity, and resolution were monitored. Many of the analytes failed to elute from the macrocyclic glycopeptide stationary phase in the absence of an additive and the most noticeable effect of increasing additive concentration was a significant decrease in retention. On the derivatized polysaccharide stationary phase the additives had little effect on retention, but they did foster significant improvements in peak shape and resolution. Chirality 15:287,294, 2003. Published 2003 Wiley-Liss, Inc. [source] Thermal decomposition of tert -butyl peroxide in a gas chromatographic reactor: A comparison of kinetic approachesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2004Peter J. Skrdla The thermal decomposition of tert -butyl peroxide is investigated utilizing both the column and the injection port of a commercial gas chromatograph (GC) as chemical reactors. Using the injector liner as the reactor, the chromatographic peak areas of the reactant, measured at various injector temperatures, are used in the determination of the activation energy of the decomposition (Ea). With the column serving as the reactor, both the reactant peak areas and the product peak shapes are similarly utilized for this purpose. Values of Ea obtained using different mathematical treatments for each of the three approaches are found to range from 115 to 164 kJ/mol. Of these methods, the column reactor approach utilizing peak area measurements (referred to as PACR, for "peak area, column reactor") is found to be far superior in terms of its speed, robustness, and its accuracy in determining Ea. The PACR method's effectiveness can be largely attributed to the mathematical treatment that is described in the approach. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 386,393, 2004 [source] Size-broadening anisotropy in whole powder pattern fitting.JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2008Application to zinc oxide, interpretation of the apparent crystallites in terms of physical models A new anisotropic size-broadening model based on a spherical-harmonics representation allowing determination of both volume- and area-averaged apparent crystallites and convenient for implementation into Rietveld programs is described. The model effectiveness is demonstrated on a ZnO powder pattern exhibiting strongly anisotropic size broadening and pronounced super-Lorentzian peak shapes. Moreover, it is shown how the apparent crystallites can be interpreted in terms of physical models by using ellipsoidal and cylindrical crystallites with lognormal size distributions. This interpretation is critically assessed and it is argued that both simplified physical models and a priori complementary information (obtained by transmission electron microscopy, for instance) are often needed to avoid unstable and non-unique solutions. [source] Scan profiles for neutron spectrometers.JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2003The recent development of neutron collimators with rectangular transmission profiles (intensity versus angular divergence) extends hope of improved count rates on neutron scattering instruments. It is usually assumed that a more effective use of beam angular spread in these devices should increase count rates by about a factor of two. However, real beams have both angular and wavevector spread and both these spreads are governed by the allowed collimation. In this extended view, the gains from ideal rectangular-profile elements (angle filters) are shown to be much larger (about a factor of four). The mirror reflections used to achieve the rectangular profiles in real devices complicate the resolution effects. Specifically, the reflections disturb the wavevector,angular divergence correlation in the beams, leading to unusual peak shapes characterized by triple peaks on powder diffractometers. Thus, these reflecting collimators are likely to be universally useful only before the monochromator and immediately preceding the detector, where wavevector,angle correlations have no effect. This reduces the potential gains to a factor of two or so. Note that the gains are as previously expected but for quite different reasons than imagined. This remains a very significant gain in a field where most work is intensity-limited. [source] Investigation of interaction between human hemoglobin A0 and platinum anticancer drugs by capillary isoelectric focusing with whole column imaging detectionJOURNAL OF SEPARATION SCIENCE, JSS, Issue 10 2008Tibebe Lemma Abstract CIEF with whole column imaging detection (WCID) was used to investigate the interaction of platinum-based anticancer drugs, cis -platinum(II) diamine dichloride (cisplatin) and [SP-4-2-{1R-trans)]-(1,2-cyclohexanediamine- N,N,)[ethanedioata(2,)- O,O,]platinum (oxaliplatin), with human hemoglobin A0 (Hb). This technique facilitates the investigation and characterization of the formation of adducts between drugs and proteins. Cisplatin and oxaliplatin were mixed with the target protein at different concentrations (0:1, 1:1, 1:10, 1:50, and 1:100), and the reaction mixtures were incubated for 0, 0.5, 1, 12, 24, 48, and 72 h at 37°C in a water-bath. The focused Hb,drug adduct profiles were imaged by WCID. At higher drug to protein molar ratios (for both oxaliplatin and cisplatin), the results exhibit significant changes in the peak shapes and heights, which may indicate the destabilization of the protein. However, the conformational change was less evident at lower molar ratios. In addition, a major pI shift was observed for the oxaliplatin reaction mixtures (for 1:10, 1:50, and 1:100 ratios). In comparison with previously reported findings obtained by other analytical methods, conclusions were drawn about the validity of CIEF as a simple and convenient method for the investigation of protein,drug interactions. These results may provide useful information for further understanding the activity and toxicity of these chemotherapeutic drugs and improving their clinical performance. [source] The detection, correlation, and comparison of peptide precursor and product ions from data independent LC-MS with data dependant LC-MS/MSPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 6 2009Scott J. Geromanos Abstract The detection, correlation, and comparison of peptide and product ions from a data independent LC-MS acquisition strategy with data dependent LC-MS/MS is described. The data independent mode of acquisition differs from an LC-MS/MS data acquisition since no ion transmission window is applied with the first mass analyzer prior to collision induced disassociation. Alternating the energy applied to the collision cell, between low and elevated energy, on a scan-to-scan basis, provides accurate mass precursor and associated product ion spectra from every ion above the LOD of the mass spectrometer. The method therefore provides a near 100% duty cycle, with an inherent increase in signal intensity due to the fact that both precursor and product ion data are collected on all isotopes of every charge-state across the entire chromatographic peak width. The correlation of product to precursor ions, after deconvolution, is achieved by using reconstructed retention time apices and chromatographic peak shapes. Presented are the results from the comparison of a simple four protein mixture, in the presence and absence of an enzymatically digested protein extract from Escherichia coli. The samples were run in triplicate by both data dependant analysis (DDA) LC-MS/MS and data-independent, alternate scanning LC-MS. The detection and identification of precursor and product ions from the combined DDA search results of the four protein mixture were used for comparison to all other data. Each individual set of data-independent LC-MS data provides a more comprehensive set of detected ions than the combined peptide identifications from the DDA LC-MS/MS experiments. In the presence of the complex E. coli background, over 90% of the monoisotopic masses from the combined LC-MS/MS identifications were detected at the appropriate retention time. Moreover, the fragmentation pattern and number of associated elevated energy product ions in each replicate experiment was found to be very similar to the DDA identifications. In the case of the corresponding individual DDA LC-MS/MS experiment, 43% of the possible detectable peptides of interest were identified. The presented data illustrates that the time-aligned data from data-independent alternate scanning LC-MS experiments is highly comparable to the data obtained via DDA. The obtained information can therefore be effectively and correctly deconvolved to correlate product ions with parent precursor ions. The ability to generate precursor-product ion tables from this information and subsequently identify the correct parent precursor peptide will be illustrated in a companion manuscript. [source] Peak quantification in surface-enhanced laser desorption/ionization by using mixture modelsPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 19 2006Martijn Dijkstra Abstract Surface-enhanced laser desorption/ionization (SELDI) time of flight (TOF) is a mass spectrometry technology for measuring the composition of a sampled protein mixture. A mass spectrum contains peaks corresponding to proteins in the sample. The peak areas are proportional to the measured concentrations of the corresponding proteins. Quantifying peak areas is difficult for existing methods because peak shapes are not constant across a spectrum and because peaks often overlap. We present a new method for quantifying peak areas. Our method decomposes a spectrum into peaks and a baseline using so-called statistical finite mixture models. We illustrate our method in detail on 8 samples from culture media of adipose tissue and globally on 64 samples from serum to compare our method to the standard Ciphergen method. Both methods give similar estimates for singleton peaks, but not for overlapping peaks. The Ciphergen method overestimates the heights of such peaks while our method still gives appropriate estimates. Peak quantification is an important step in pre-processing SELDI-TOF data and improvements therein will pay off in the later biomarker discovery phase. [source] The detection of phenotypic differences in the metabolic plasma profile of three strains of Zucker rats at 20 weeks of age using ultra-performance liquid chromatography/orthogonal acceleration time-of-flight mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2006Robert S. Plumb Analysis of biological fluids using ultra-performance liquid chromatography/mass spectrometry (UPLC/MS) (metabonomics) can allow new insights to be gained into disease processes, with advances in chromatographic techniques enabling the detection of thousands of metabolites. In this work metabonomics has been used to investigate the metabolic processes involved in type II diabetes in the Zucker obese rat. Plasma was analyzed from three different strains, the Zucker (fa/fa) obese, Zucker lean and the lean/(fa) obese cross. Using UPLC/MS, ca. 10,000 ions were detected due to the narrow peak widths and excellent peak shapes achieved with this technology. Confidence in the chromatographic performance was demonstrated by the use of quality control standards. The positive and negative ion total ion chromatograms obtained from the three strains were readily distinguishable using multivariate statistical analysis. The greatest difference was observed between the Zucker lean and Zucker lean/(fa) rats compared to the Zucker (fa/fa) obese rats. Positive ions m/z 220 (4.36,min), 282(3.78,min), 359 (5.33,min) and 405 (7.77,min) were elevated in the plasma derived from Zucker lean rats whilst ions m/z 385 (6.80,min) and 646 (4.36,min) were at a lower concentration compared to the plasma from the Zucker (fa/fa) obese animals. Negative ions elevated in the Zucker lean rats included m/z 212 (2.30,min), 514 (2.85,min), 295 (4.39,min), 329 (3.11,min), 343 (2.86,min) and 512 (2.86,min) with ions m/z 538 (4.18,min), 568 (4.18,min), 568 (5.09,min) and 612 (4.30,min) being raised in the samples derived from Zucker (fa/fa) obese animals. The ion m/z 514 (3.85,min) was found to correspond to taurocholate, providing further support for an involvement of taurine metabolism in diabetes. Copyright © 2006 John Wiley & Sons, Ltd. [source] HPLC of basic drugs using non-aqueous ionic eluents: evaluation of a 3,,m strong cation-exchange materialBIOMEDICAL CHROMATOGRAPHY, Issue 3 2010Phillip E. Morgan Abstract HPLC columns packed with 3,,m particle size HPLC Technology Techsphere SCX (propylsulfonic acid-modified) silica offer considerable advantages over 5,,m SCX packings in the analysis of basic drugs using 100% methanol eluents containing an ionic modifier such as ammonium perchlorate. The basic drugs studied included clozapine and norclozapine, olanzapine, quinine and quinidine, and amitriptyline, nortriptyline, imipramine and desipramine. The 3,,m column was not only more efficient for a given column length compared with 5,,m materials, but also elution times were less, a phenomenon observed in reversed-phase systems. The high efficiencies and excellent peak shapes obtained with the 3,,m SCX-modified packing together with the relatively low back-pressures attained show that such materials deserve serious consideration by laboratories involved in the analysis of basic drugs. Manufacturers should offer such packings as a matter of routine. Alternative ionic modifiers such as ammonium acetate are available for use with mass spectrometric detection if required. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||