No abstract
Field-desorption mass spectrometry has been used to characterize polystyrene oligomers of molecular weight up to 15 000 Da. The technique shows good agreement with molecular weight data calculated using vapour-phase osmometry and gel-permeation chromatography but in addition provides much more detailed information in terms of oligomer distribution and the nature of end groups present in the oligomers.Field-desorption mass spectrometry (FDMS) has been used in the characterization of synthetic polymers',* and has been able to provide information on the repeat units involved, average molecular weights and oligomer distribution. The technique's ability to generate only molecular or quasi-molecular ions makes it a particularly appropriate method in the characterization of oligomeric/polymeric species.Earlier FDMS studies3 involving polystyrene oligomers have demonstrated the analysis of these at molecular weights up to 10 000 Da while a slightly later study4 demonstrated the use of the technique in the determination of oligomer distributions up to 5300 Da and its capabilities in the calculation of average molecular weight data. Costello et al.,' have also reported the utility of FDMS in the characterization of a range of polymeric materials and the subsequent calculation of average molecular weights. The availability of the present generation of double-focusing mass spectrometers combining high sensitivity field-desorption ion sources with high mass (> 10 000 Da) analysers and high sensitivity detectors has prompted our group to revisit some of the issues involved in the analysis of polystyrene oligomers. EXPERIMENTAL Chemicals.The polystyrene samples included in this study were gel-permeation chromatography (GPC) standards supplied by Polymer Laboratories Ltd, Church Stretton, UK. These materials are characterized by the manufacturers as indicated in Table 1. Author to whom correspondence should be addressed.Mass spectrometry. All mass spectra were recorded using a model ZAB2-SE reversed geometry mass spectrometer (VG Analytical Ltd, Wythenshawe, UK) equipped with the standard VG combined fi" desorption/fast-atom bombardment (FD/FAB) source. The samples were analysed using 10 pm activated carbon FD emitters supplied by Linden ChroMasSpec (Bremen, FRG) and the sample was applied to the emitter using the standard syringe technique. The standards were prepared as solutions in toluene. The emitter was typically programmed from 0-40 mA or until the signal intensity disappeared. All data were acquired at a resolution of 1000. Data were acquired into the VG Opus datasystem in multichannel analysis (MCA) mode. Gel-permeation chromatography (GPC). All four samples were characterized by GPC using a 30 cm X 7.5 mm ID polystyrene/divinylbenzene GPC column (500 A pore size) in series with a 10OOOA pore-size column. Stabilized tetrahydrofuran was used as the eluant at a flow rate of 1cm3/min. This was delivered using a Knauer high-performance liquid chromatography system and detection was achieved by a refractiveindex detector. R...
Cu2+ derived from aqueous CuC1, solutions and supported upon silica and anatase, but not alumina, shows asymmetric e.s.r. peaks and an absence of X.P.S. shake-up satellite peaks. Consideration is given to whether this may be attributed in part to its higher dispersion and different constrained symmetry. Divalent copper is stabilised by these oxide supports but in two different forms : one highly dispersed (with properties detectable by X.P.S. and e.s.r.) and the other poorly dispersed [as Cu,(OH),CI-type species on alumina and CuCl, on silica and anatase] characterisable by X.r.d. In respect to its effect upon the X.P.S. and reduction (but not e.s.r.) properties of supported Cu2+ species, rutile is different from anatase, a phenomenon which may be of some value in optimising activity of heterogeneous catalysts. The results cast doubt upon X.P.S. diagnosis of divalent copper. Resistivity measurements for titania-supported copper after reduction at 700 K suggest that very little of the copper may have been intercalated into the anatase support, but that on rutile such an intercalation may have been significant. This may be relevant to SMSI effects, especially at even higher reduction temperatures.
Precursor-ion scanning, in which all ions that fragment to form a selected product ion are detected, has been implemented on a four-sector instrument. The various experimental parameters associated with the experiment i.e., precursor mass range, product and precursor ion resolution, collision energy and mass-measurement accuracy have been established via a series of experiments. Brief examples of the use of the technique in the characterization of synthetic polymers, quaternary salts and peptides are described together with the analysis of a mixture of phthalate esters.One of the major uses of tandem mass spectrometry (MS/MS) has been in the analysis of complex mixtures' and in structural studies. By far the most utilized mode of MS/MS analysis has been product-ion scanning, but use has also been made of precursor-ion scans in which, for example, phthalate esters are characterized by the observation of m/z 149 which is a characteristic ion in the product-ion spectra of this compound c l a s~.~-~ By using a precursor-ion scan of m/z 149, the identities of various phthalate esters in a complex mixture have been established.Precursor-ion scans may be easily implemented on a triple-quadrupole instrument with unit mass resolution of both precursor ions and product ions being obtained. They have also been implemented on various hybrid instruments in which a quadrupole collision cell and analytical quadrupole follow a double-focusing instrument. Here unit mass resolution of the selected product ion can be combined with medium mass resolution (a few thousand) of the precursor ions. Both triplequadrupole and hybrid instruments have access only to low-energy collision regimes. Precursor-ion scans can also be performed on a two-sector instrument using a linked scan at constant B 2 / E which gives a precursorion resolution of only a few hundred at best' but has the advantage of kilovolt collision energies.The use of multi-sector instruments has been limited to product-ion spectra only, despite the potential advantages of such instruments in terms of accessible mass range, the possibility of using kilovolt collision energies, and obtainable resolution. Precursor scans on a four-sector instrument may be carried out in two ways. The first is to scan both magnets simultaneously in opposite directions, but the difficulty of maintaining the correct relationship between B, and B2 has discouraged this approach in practice.The second approach is to use an electrically floated collision cell and make use of the energy transmission window of MS2 to transmit simultaneously a product mass with a range of energies determined by the masses of its precursors.* Author to whom correspondence should be addressedWe have been able to make use of the exceptionally wide energy acceptance of MS2 on the ZAB-T tandem instrument (VG Analytical Ltd, Manchester, UK) to implement precursor-ion scanning in this way, with collision energies as high as 2 keV. Examples of data which establish the performance of this approach are presented here. EXPERIMENTALT...
Polyester films are well-known substrates for a wide range of electronic applications. This contribution will describe new developments in polyester film substrates for OLED displays.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.