Selective Analysis (selective + analysis)

Distribution by Scientific Domains

Selected Abstracts


J. E. Frawley
Background: The aim of the present study was to investigate the role of potential clinical risk factors in the causation of peri-operative stroke associated with carotid endarterectomy. With the change in carotid endarterectomy practice from the use of a shunt to high-dose thiopental for cerebral protection (a previously undocumented method), it was essential to identify accurately the causes of all peri-operative strokes. Methods: A prospective audit was undertaken of 1000 carotid endarterectomies in which the causes and pathology of all peri-operative strokes were documented. The roles of advanced age, female gender, hypertension, previous stroke, contralateral carotid stenosis > 70%, and contralateral carotid occlusion as potential causes of peri-operative stroke were defined. Results were statistically analysed using odds ratio and Fisher's exact test. Results: None of the potential risk factors was statistically significant for peri-operative stroke. Female gender was associated with a significant risk of peri-operative stroke due to operative site thrombosis. Complications at the endarterectomy site were the commonest cause of stroke. Conclusions: Prospective audit is a useful tool for identifying causes of peri-operative stroke and indicating the need for modifications to surgical clinical management which might improve outcomes for carotid endarterectomy. [source]

Selective Analysis of Secondary Amines Using Liquid Chromatography with Electrochemical Detection (LC-EC)

Abstract In a mixture of primary and secondary aliphatic amines, the primary amines were derivatized (masked) with o -phthalaldehyde (OPA) followed by derivatization of the remaining secondary amines with ferrocenecarboxylic acid chloride (FAC). The "tagged" amines were analyzed by LC-EC (liquid chromatography with electrochemical detection) using in-series dual electrode detection. Chemically-reversible oxidation of the FAC tagged secondary amines and their subsequent complementary oxidation and reduction signals coupled with chemically-irreversible oxidation of OPA tagged primary amines provided the selectivity for quantitative secondary amine analysis. The procedure was also applied for the selective identification of fragment 4,11 (N -terminus-proline) of Substance P in the presence of other Substance P fragments with primary amino acids as their N -termini. [source]

Selective analysis of phosphopeptides within a protein mixture by chemical modification, reversible biotinylation and mass spectrometry

Maceij Adamczyk
A new method combining chemical modification and affinity purification is described for the characterization of serine and threonine phosphopeptides in proteins. The method is based on the conversion of phosphoserine and phosphothreonine residues to S -(2-mercaptoethyl)cysteinyl or ,-methyl- S -(2-mercaptoethyl)cysteinyl residues by ,-elimination/1,2-ethanedithiol addition, followed by reversible biotinylation of the modified proteins. After trypsin digestion, the biotinylated peptides were affinity-isolated and enriched, and subsequently subjected to structural characterization by liquid chromatography/tandem mass spectrometry (LC/MS/MS). Database searching allowed for automated identification of modified residues that were originally phosphorylated. The applicability of the method is demonstrated by the identification of all known phosphorylation sites in a mixture of ,-casein, ,-casein, and ovalbumin. The technique has potential for adaptations to proteome-wide analysis of protein phosphorylation. Copyright 2001 John Wiley & Sons, Ltd. [source]

Direct on-line analysis of neutral analytes by dual sweeping via complexation and organic solvent field enhancement in nonionic MEKC

Jun Cao
Abstract Conventionally, neutral compounds cannot be separated by nonionic micelle capillary electrophoresis. In this report, the development of a novel on-line preconcentration technique combining dual sweeping based on complexation and organic solvent field enhancement is applied to the sensitive and selective analysis of three neutral glucosides: ginsenoside Rf, ginsenoside Rg1, and ginsenoside Re. Nonionic micelle detectability by CE is demonstrated through effective focusing of large sample volumes (up to 38% capillary length) using a dual sweeping mode. This results in a 50- to 130-fold improvement in the LODs relative to conventional injection method. Neutral compounds sweeping is examined in terms of analyte mobility dependence on borate complexation, solvent viscosity difference, and Brij-35 interaction. Enhanced focusing performance by this hyphenated method was demonstrated by a greater than fourfold reduction in glucoside bandwidth, as compared with common sweeping (devoid of organic solvent-mediated sweeping method in the sample matrices). Moreover, separation efficiencies greater than a million theoretical plates can be achieved by sweeping large sample volumes into narrow zones. The designated method was also tested for its ability to determine the presence of glucosides in the crude extracts obtained from plant sample. [source]

New supported liquid membrane-capillary electrophoresis in-line arrangement for direct selective analysis of complex samples

Leonor Nozal
Abstract An in-line coupling of a micro-membrane extraction unit, based on supported liquid membrane, with commercially available capillary electrophoresis equipment is described. A main characteristic of this micro-membrane device, made from a simple Eppendorf tube, is that it permits the application of voltage in the acceptor solution to be applied during the extraction process. This has been shown as an alternative to enhance sensitivity, as the analytical signal achieved by applying 10,kV for 20,min was similar to that obtained without the application of voltage and with extraction time of 60,min. In addition, the design has been made permitting both in-line hydrodynamic and electrokinetic sample introduction into the electrophoretic capillary. The analytical potential of the proposed system has been demonstrated by the direct determination of nitroimidazoles from pig liver tissue. The high efficiency of the proposed system allowed the extraction and the determination of the analytes to be performed from a simple tissue homogenate obtained in water. The precision of the analysis of spiked samples, expressed in terms of relative standard deviation, was better than 4.8%. [source]

Analysis of alcohols, as dimethylglycine esters, by electrospray ionization tandem mass spectrometry

Dr David W. Johnson
Abstract Dimethylglycine (DMG) esters are new derivatives for the rapid, sensitive and selective analysis of primary and secondary alcohols, in complex mixtures, by electrospray ionization tandem mass spectrometry (ESI-MS/MS). Their development was inspired by the use of the complementary dimethylaminoethyl esters for the trace, rapid analysis of fatty acids. DMG esters are simply prepared by heating a dichloromethane solution of the imidazolide of dimethylglycine, containing triethylamine, and an alcohol. DMG esters of long-chain fatty alcohols, isoprenoidal alcohols and hydroxy-acids are analysed by electrospray ionization tandem mass spectrometry with a precursor ion of m/z 104 scan. Diols, glyceryl esters, glyceryl ethers and some sterols are analysed by a neutral loss of 103 Da scan. Trimethylglycine (TMG) ester iodides, prepared by alkylation of DMG esters with methyl iodide, are more sensitive derivatives for molecules containing secondary alcohol groups, such as cholesterol and gibberellic acid. They are analysed by a precursor ion of m/z 118 scan. DMG or TMG derivatives were shown to be at least comparable and sometimes an order of magnitude more sensitive than N -methylpyridyl ether derivatives for ESI-MS/MS analysis of the different classes of alcohols. Applications of these derivatives for the diagnosis of inherited disorders and the analysis of natural products are presented. Copyright 2001 John Wiley & Sons, Ltd. [source]

HPLC-MS of anthraquinoids, flavonoids, and their degradation products in analysis of natural dyes in archeological objects

Izabella Surowiec
Abstract LC with MS detection was optimized for sensitive and selective analysis of main classes of natural dyes used in ancient times for dyeing textiles , red anthraquinoids, yellow flavonoids, and known degradation products of flavonols , hydroxybenzoic acids. Fragmentation patterns of both negative and positive molecular ions for the above mentioned compounds were investigated. Three acquisition modes of MS analysis: scanning, SIM, and multiple reaction monitoring (MRM) in both positive and negative ion modes were optimized and compared with each other and with the UV-Vis diode-array detection. Even though in the applied chromatographic system formic acid was used in the mobile phase, SIM in the negative ion mode was the most selective and sensitive detection for all the investigated compounds when both mixtures of standards and analysis of extracts from archeological samples were concerned, with one exception , alizarin, for which MS detection in positive ion mode was more sensitive. Detection limits obtained with MS detection for all investigated compounds except quinizarin were lower than the ones obtained with the diode-array UV-Vis detection, making MS detection the most suitable tool for the analysis of natural dyes and their degradation products in extracts from archeological samples. [source]

Molecularly imprinted polymers for selective analysis of chemical warfare surrogate and nuclear signature compounds in complex matrices

Scott D. Harvey
Abstract This paper describes the preparation and evaluation of molecularly imprinted polymers (MIPs) that display specificity toward diisopropyl methylphosphonate (DIMP) and tributyl phosphate (TBP). Polymer activity was assessed by solid-phase extraction and high-performance liquid chromatography experiments. Both DIMP- and TBP-specific vinylpyridine-based MIPs selectively retained their targets relative to a non-imprinted control. Proof-of-principle experiments demonstrated highly selective analysis of the targets from fortified complex matrix samples (diesel fuel, gasoline, and air extract concentrate). The retained MIP fractions gave near quantitative recovery of the target analytes with very low matrix background content. The same fraction from the control sorbent recovered only about half of the analyte and tended to be less pure. [source]

Circulating CD10,/CD16low neutrophils provide a quantitative index of active bone marrow neutrophil release

Y. Orr
Summary Circulating neutrophil phenotype and function are altered during neutrophilia associated with acute inflammatory states, however, the contribution of bone marrow neutrophil release to these changes has been difficult to quantify in humans. Accelerated release of neutrophils, with potentially distinct attributes, from the bone marrow and their dilution within the circulating pool may produce these apparent changes. Unfortunately selective analysis of these newly emergent neutrophils is difficult given their morphologic similarity to those already in the circulation and the coincident effect of soluble inflammatory mediators on circulating neutrophil phenotype and function. Using whole blood flow cytometry and cardiac surgery as an inflammatory stimulus, we demonstrate the emergence of a unique subpopulation of circulating neutrophils characterised as CD10,/CD16low, indicative of active bone marrow neutrophil release peri-operatively. CD10,/CD16low neutrophils emerge at the same operative stages as band forms and a left shift, yet represent over 40% of circulating neutrophils postoperatively, and generate a greater stimulus-induced [Ca2+]i flux than their CD10+ counterparts. We conclude that CD10,/CD16low neutrophils represent a significant proportion of the circulating pool after cardiac surgery and that bone marrow release, a major contributor to neutrophilia, influences the phenotype and functional activity of circulating neutrophils following this acute inflammatory stimulus. [source]