Search results for "Spectrometry"
showing 10 items of 3206 documents
SPM and TOF-SIMS investigation of the physical and chemical modification induced by tip writing of self-assembled monolayers
2003
Abstract The nanoelectrochemical modification of alkyl self-assembled monolayers (SAMs) obtained on hydrogenated silicon surfaces via radical-initiated reactions of 1-octadecene has been investigated. Scanning Probe Microscopy (SPM) showed that the modification of the organic layer occurs by applying either positive or negative biases to the tip at a threshold of about ±5 V. When the bias absolute value was ≤6 V, the height of the monolayer was only faintly modified, whereas a consistent increase in tip/sample friction force was observed, in agreement with the formation of hydrophilic moieties at the organic surface. In addition to the increase of friction, bias absolute values larger than …
Copolyamides from adipic and truxillic acids: Synthesis and characterization by direct pyrolysis in the mass spectrometer
1977
The synthesis of a series of polyamides and copolyamides containing α-truxillic and adipic units in the chain is reported. The thermal degradation of these polymers was investigated by direct pyrolysis in the ion source of a mass spectrometer. Thermal degradation reactions were followed directly by this method by detecting the thermal- and electron-impact-induced fragments. The results obtained show a good correlation between the intensity of mass peaks characteristic of truxillic and adipic moieties and the composition of the copolyamides, as ascertained by elemental analysis. This is an important result since it shows the potential of the direct pyrolysis method in the analysis of copolym…
Mass spectra of halogenated esters 6—Methyl esters of some trihalogenated propanoic and butanoic acids
1984
The mass spectral fragmentation of trihalogenated methyl esters, formed in the reactions of monochlorinated methyl propenoates and 2-butenoates with Cl2, BrCl and Br2, have been investigated. In most cases α-cleavage gives the base peak, [COOCH3]+, the peaks originating from the subsequent losses of one or two halogen atoms also being abundant. The primary loss of a halogen atom is more prominent in the C4 derivatives, Br˙ and Cl˙ being preferentially lost from the 2- and 3-positions, respectively. The McLafferty rearrangement yields in one case the base peak; the 2-halo compounds could in general be distinguished by that fragmentation. Typical for all 2-bromo-substituted methyl butanoates …
Pyrolysis gas chromatography-mass spectrometry in environmental analysis: Focus on organic matter and microplastic
2020
Pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) has great potential within environmental analysis. This technique is mainly used for the chemical identification of macromolecules that cannot be characterized by either liquid or gas chromatography due to their big size. Through pyrolysis (controlled thermal degradation), these macromolecules are broken down into simpler molecules that can be separated by gas chromatography and detected by mass spectrometry. This technique has been traditionally used in environmental samples for the characterization of organic matter and humic substances, contaminants, lignins, etc. It attains the identification of the different types of chemical un…
Electrospray ion mobility mass spectrometry of positively charged sodium bis[2-ethythexyl)sulfosuccinate aggregates.
2014
Collision cross-sections (CCS) of positively singly and multiply charged aggregates of the surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOTNa) in the gas phase have been measured by quadrupole ion mobility time-of-flight mass spectrometry. Calibration of the observed drift times to the CCS of the AOTNa non-covalent aggregates was achieved by collecting, under the same experimental conditions, the drift times of a range of singly and multiply charged polyalanine peptides whose CCS had been obtained by conventional ion mobility spectrometry. Together with an obvious increase of the aggregate cross-section with the aggregation number, it was found that the aggregate cross-section increa…
Normal-phase (temperature gradient) interaction chromatography – A powerful tool for the characterisation of high molecular weight chain-end function…
2015
Abstract We report here, for the first time, quantitative analysis of end-group functionalisation and the extent of end-group modification of polymers with molar mass up to 200,000 g mol −1 , using a combination of isothermal and temperature gradient interaction chromatography. At such high molecular weights, other common analytical techniques such as MALDI-ToF-MS and NMR spectroscopy are simply unable to offer any quantitative insight into the end-group functionality of polymers. Thus, normal phase isothermal interaction chromatography (NP-IIC) has been used to characterise a series of polystyrene samples, with identical molar mass (c. 90,000 g mol −1 ), each carrying a single chain-end fu…
Polymeric gegenions induced variability and mobility of amphiphilic supramolecular structures on solid substrates
1992
Abstract The micromorphological variations of amphiphilic L -glutamate derivatives at air-substrate interfaces due to an adjacent mobile polymer matrix have been investigated via fluorescence microscopy. Adjusted monolayers of the L -glutamate derivatives have been transferred by LB technique out of different aggregation states onto various substrates. The substrates have been prepared by successive polymer preadsorption to the solid support. The influence of the adjacent polymer layers on the domain morphology as a function of water content and temperature has been examined intensively. Moreover, reversible domain changes induced by temperature variation of the transferred films have been …
Stabilisation of LDPE cross-linked in the presence of peroxides III. Mass spectrometric study of chemical changes taking place in the n-octadecane–di…
2000
Abstract An attempt was made to identify the products of the reaction between dicumyl peroxide and Irganox 1081, carried out in n -octadecane (saturated hydrocarbon), in conditions of fast decomposition of the peroxide (180°C, 5 min). Mass spectrometry (MS) was employed to find m/z values of molecular and fragment ions in analyses of the components ( n -octadecane, dicumyl peroxide, Irganox 1081) and of the following systems: n -octadecane–dicumyl peroxide, n -octadecane–Irganox 1081 and n -octadecane–dicumyl peroxide–Irganox 1081, after holding them at a temperature of 180°C for 5 min. The tendency of sulphur in Irganox 1081 to oxidise, specifically in the presence of dicumyl peroxide, was…
Capillary electroendoosmotic chromatography of peptides
2000
This review focuses on the current state of peptide separation by capillary electroendoosmotic chromatography (CEC). When carried out under optimised conditions, peptide separation by CEC methods represents an orthogonal and complementary technique to micro-HPLC (micro-HPLC) and high-performance capillary zone electrophoresis (HPCZE). The origin of the selectivity differences that can be achieved with these three separation techniques (CEC, micro-HPLC and HPCZE), respectively are discussed, and the current limits of performance with CEC methods documented. Peptide separations by CEC methods with n-alkyl bonded silicas or mixed-mode phases are also illustrated. The development of different v…
Temperature triggered self-assembly of polypeptides into multivalent spherical micelles.
2007
We report herein thermally responsive elastin-like polypeptides (ELPs) in a linear AB diblock architecture with an N-terminal peptide ligand that self-assemble into spherical micelles when heated slightly above body temperature. A series of 10 ELP block copolymers (ELP(BC)'s ) with different molecular weights and hydrophilic-to-hydrophobic block ratios were genetically synthesized by recursive directional ligation. The self-assembly of these polymers from unimers into micelles was investigated by light scattering, fluorescence spectroscopy, and cryo-TEM. These ELP(BC)'s undergo two phase transitions as a function of solution temperature: a unimer-to-spherical micelle transition at an interm…