The characterization of polystyrene oligomers by field‐desorption mass spectrometry

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...

The characterization of complex mixtures by field desorption-tandem mass spectrometry

“…6 Furthermore, CID spectra from oligomers, with molecular weights of up to 1620 Da, have been shown previously and fragmentation pathways proposed. 7 Figure 1 1306, of the 12-mer of poly(styrene) A (1) which was obtained in the hybrid sector-oa-TOF instrument.…”

“…Another commonly encountered class of alkyl esters are those produced from adipic acid (6). An example of the FD-MS/MS spectrum of this type of ester, namely di-iso-decyl adipate, is shown in Fig.…”

Electrospray tandem mass spectrometry of poly(3-hydroxybutanoic acid) end groups analysis and fragmentation mechanism

“…1 The utility of this technique has been extended due to the development of modern ion trap systems 2,3 and new soft ionization methods such as field desorption, 4 matrix-assisted laser desorption/ionization (MALDI), 5,6 secondary-ion mass spectrometry 7 and electrospray ionization (ESI). 8 The latter technique has recently been applied to poly(ethylene glycol), 8 poly(methyl methacrylate) 9 and polystyrene 10 analysis.…”

Utilising time-lag focusing ultraviolet-matrix-assisted laser desorption/ionisation ­ mass spectrometry for the end group analysis of synthetic polymers

“…The ions observed in the FD-MS spectrum were molecular ions, M+ . [23], whereas adducts with silver ([M+Ag]+) are seen by means of MALDI-MS. These spectra indicate that there is no significant mass dependence of the detector over this mass range.…”

“…The use of time-lag focusing significantly improves the resolution and signal-to-noise that is observed. A spectrum of a sample of similar average molecular weight was obtained by means of FD-MS [23]. The ions observed in the FD-MS spectrum were molecular ions, M+ .…”