Search results for "ionization"
showing 10 items of 1255 documents
Structural „memory effects” influencing decompositions of glucose alkoxide anions produced from monoterpene glycoside isomers in tandem mass spectrom…
1989
Isomeric glycoconjugates have been distinguished using desorption negative-ion chemical ionization/tandem mass spectrometry (DNCI–MS/MS). The structure of the leaving terpene influences the orientation of consecutive decompositions during collisionally activated decomposition (CAD) of [M–H]− ions which pass through a glucose alkoxide intermediate ion. This apparent „memory effect” can be rationalized by considering the production of anion-induced dipole complexes.
A strategy for chromatographic and structural analysis of monosaccharide species from glycoproteins.
1996
A general strategy for the chromatographic and structural analysis of the monosaccharide species fucose (Fuc), N-acetylgalactosamine (GalNAc), N-acetylglucosamine (GlcNAc), galactose (Gal), glucose (Glc), mannose (Man), N-acetylneuraminic acid (NANA) present in glycoproteins is described. Qualitative and quantitative aspects for the separation of these glycoprotein monosaccharides (monosaccharide species) using ligand-exchange chromatography (LEC) and high pH anion-exchange chromatography (HPAEC) in combination with pulsed-amperometric detection (PAD), refractive index (RI) and ultraviolet (UV) monitoring are discussed in detail. The conditions for the acidic hydrolysis of glycoproteins and…
Direct observation and thermal transformations of dications derived from dibenzotropylium ions
1992
Abstract Carboxylic acid 1 and its derivatives 2 , 3 treated with triflic acid below −20°C afford the dications 1H 2+2- 3H 2+2. Cyclodehydration above 20°C (or in the gas-phase, CIMS of 3 ) leads to the diprotonated ketone 4H 2+2.
Micro-Raman spectroscopic characterization of a CR-39 detector.
2013
Characterization by micro-Raman spectroscopy of polymeric materials used as nuclear track detectors reveals physico-chemical and morphological information on the material's molecular structure. In this work, the nuclear track detector poly(allyl diglycol carbonate), or Columbia Resin .39 (CR-39), was characterized according to the fluence of alpha particles produced by a 226Ra source and chemical etching time. Therefore, damage of the CR-39 chemical structure due to the alpha-particle interaction with the detector was analyzed at the molecular level. It was observed that the ionization and molecular excitation of the CR-39 after the irradiation process entail cleavage of chemical bonds and…
Characterization of gas phase aggregates of bis(2-ethylhexyl)sulfosuccinate (AOT) and divalent metal ions. Elimination of radical species in the deco…
2012
Structure and properties of even-electron anionic species formed by bis(2-ethylhexyl)sulfosuccinate (AOT) and divalent metal ions (MII) with stoichiometry [AOTMIICl2]– have been investigated by using electrospray ionization and different mass spectrometry techniques, such as high resolution, accurate mass measurements, collision-induced dissociation (CID) multiple-stage mass spectrometry. Owing to CID, eliminations of neutrals, mainly consisting in hydrochloric acid, 2-ethyl-1-hexene and 2-ethylhexanol, and an unexpected loss of an alkyl radical have been observed. The radical anions [C4HO6SMIICl]–• so produced have been characterized by MS3 experiments. Density functional theory calculatio…
Hydrophobic and cation exchange mechanisms in the retention of basic compounds in a polymeric column.
2004
A cation exchange retention mechanism concomitant with the well-known hydrophobic partition mechanism in a polymeric column has been observed and investigated. This exchange process is attributed to ionization of some acidic sites present in the polymer column at basic mobile phase pH values. Several drugs of different basicity have been chromatographed on a polymeric PLRP-S column with methanol-water and acetonitrile-water mobile phases. The cation exchange between the protonated basic drug and the buffer cations (Na+, K+ and BuNH4+) is observed at the pH range where the protonated drug and the ionized sites of the column coexist. This process produces a shift of the retention versus pH pl…
Analytical study of proteinaceous binding media in works of art by gas chromatography using alkyl chloroformates as derivatising agents.
2001
In this work, we present the results obtained in an analytical study of the different types of proteinaceous binding media most commonly used in paintings, using GC-FID as the technique of analysis and GC-MS as a confirmatory technique. The application of this methodology requires prior hydrolysis of the proteins in the binding media to obtain free amino acids and then volatile derivatives, in this case by reaction with chloroformates due to advantages of speed, safety and the aqueous medium in which the reaction occurs. The method proposed for the proteinaceous binding media study is to calculate the proportions of the different amino acids with respect to alanine. This method provided goo…
Evaluation of the quality of olive oil using fatty acid profiles by direct infusion electrospray ionization mass spectrometry
2008
Abstract Electrospray ionization mass spectrometry is used to predict the olive oil quality according to European Union marketing standards. Samples were 1:50 diluted in an alkaline 85:15 (v/v) propanol/methanol mixture and directly infused into the electrospray ionization source of an ion trap mass spectrometer. The establishment of ratios of the peak abundances of the free fatty acids followed by linear discriminant analysis was employed to predict the olive oil quality grade. In addition, using multiple linear regression and partial least-squares regression, the percentages of extra virgin and virgin olive oils in binary mixtures were predicted with 5–11% average prediction errors.
Selective extraction of small proteins from biological samples using a novel restricted access column with cation exchange properties
2000
The determination of proteins utilising a polymer-based restricted access suppor material with ion exchange properties (IERAM) is outlined. Solid phase extraction coupled on-line with a mincrobore reversed phase HPLC system for the quantitation of small marker proteins is demonstrated. The cation-exchange restricted access packings were characterised with respect to their adsorption and desorption kinetics. The IERAM material was also investigated by capacity, selectivity, and biocompatibility determinations when applied to the quantification of small molecular weight proteins such as cytochrome C, Lysozyme, Ribonuclease A, Myoglobin, Insulin, human serum albumin, and a Tryptic inhibitor.
Prediction of the genetic variety of Spanish extra virgin olive oils using fatty acid and phenolic compound profiles established by direct infusion m…
2007
Abstract The genetic varieties of Spanish extra virgin olive oils (Arbequina, Hojiblanca and Picual) were predicted by direct infusion of the samples in the electrospray ionization source of a mass spectrometer, followed by linear discriminant analysis of the spectral data. The samples were 1:50 diluted (v/v) with an 85:15 propanol/methanol (v/v) mixture containing 40 mM KOH and infused. The abundances of the [M–H] − peaks of the free fatty acids (7 peaks) and 28 phenolic compounds (20 peaks) were measured. Ratios of pairs of peak abundances were used as predictors in the construction of the linear discriminant analysis models. An excellent resolution between the three genetic varieties was…