Atmospheric solid analysis probe mass spectrometry vs electrospray tandem mass spectrometry of polydimethylsiloxanes in positive and negative ionization modes

Abstract

Atmospheric solid analysis probe mass spectrometry vs electrospray tandem mass spectrometry of polydimethylsiloxanes in positive and negative ionization modes Atmospheric solid analysis probe [1] (ASAP) has been found to be promising for the analysis of polymers exhibiting poor electrospray ionization (ESI) efficiency.[2] Due to pyrolysis processes in ASAP, [3] polymers undergo extensive fragmentation and the resulting fragment ions are limited to the low m/z range.[2] Single-stage ASAP-MS would thus have some analogy with tandem mass spectrometry (MS/MS) coupled to a soft ionization technique such as ESI. Here we report the ASAP-MS analyses of symmetric polydimethylsiloxane chains (PDMS) terminated with hydroxy and ethoxy groups (further noted (H,OH)-and (Et,OEt)-PDMS, respectively) in positive and negative ionization modes (ASAP(+/-)-MS), and the results compared with the ESI(+/-)-MS/MS spectra of ammonium adducts reported previously. [4] In particular, ASAP-MS analyses of (H,OH)-PDMS of high molecular weights exceeding 100,000 g mol -1 and (Et,OEt)-PDMS not prone to ESI in the negative ion mode will be discussed based on the ESI data.(H,OH)-PDMS samples of weight average molecular weights (M w ) 18,000 and 110,000 g mol -1 were purchased from Scientific Polymer Products Inc. (Ontario, NY, USA), while three others (M w = 400-700, 4,200 and 49,000 g mol -1 ) and (Et,OEt)-PDMS (800-900 g mol -1 ) were from ABCR GmbH & Co. KG (Karlsruhe, Germany). ASAP-MS data were acquired using a hybrid quadrupole/time-of-flight SYNAPT G2 HDMS mass spectrometer (Waters Corp, Manchester, UK) fitted with an ASAP source conditioned for 1 h at the working temperature and gas flow rate before analysis.[2]The ASAP capillary tube was dipped in the pure polymer before its fixation to the probe holder and introduction into the ionization source (source temperature: 140°C; nitrogen flow rate: 1200 L h -1 at 650°C; corona discharge voltage: 4 kV; sampling cone voltage: 20 V; instrument control: MassLynx 4.1). ESI-MS/MS experiments were performed using a QStar Elite hybrid quadrupole orthogonal acceleration time-of-flight mass spectrometer from Applied Biosystems/SCIEX (Concord, ON, Canada) equipped with an ESI source (capillary voltage +5,500 V/-4,500 V, cone voltage at +50 V/-20 V, methanolic solution of ammonium acetate (39 μg L -1 ) and PDMS (10 μg L -1 ) injected at a flow rate of 5 μL min -1 ; instrument control: Analyst QS 2.0). Collision-induced dissociation (CID) experiments were conducted with nitrogen as the collision gas. The collision energies mentioned for the ESI-MS/MS spectra are in the center-of-mass frame E cm = E lab × m nitrogen /(m nitrogen + m ion ).According to the nomenclature defined by Wesdemiotis and co-workers for product ions generated during MS/MS of synthetic polymers, [5] and owing to the symmetry of the endgroups, only a n and b n product ion series can be expected to form from either (H,OH)-or (Et,OEt)-PDMS (Scheme 1). ), a versatile reference compound that can be successfully mass analyzed regardless of th...

Advances in Ionization for Mass Spectrometry

“…Fouquet et al compared ASAP-MS with ESI-MS/MS and found the methods to be complementary for polydimethylsiloxanes with M w between 18 000 and 110 000 due to the fragmentation produced during the ASAP thermal vaporization and ionization processes. 104 ASAP IMS-MS was evaluated as a method to characterize poly(ether ether ketone) polymers by Cossoul et al 105 This solvent-free approach produced almost identical end group assignments and relative ion abundances as MALDI which, unlike ASAP, requires use of strong solvents such as sulfuric acid to first dissolve the polymer. A cyclic olefin copolymer grafted with aryl layers was characterized by Vieillard et al using ASAP in combination with IMS-MS among other analytical methods.…”

High‐performance thin‐layer chromatography with atmospheric solids analysis probe mass spectrometry for analysis of gasoline polymeric additives

“…Since 2005, ASAP has grown in popularity since it permits the direct analysis of a wide range of samples and in particular polymers. [29][30][31][32][33] For instance, synthetic polymers have been efficiently analysed using ASAP and their polydispersity evaluated. 34 More recently, a rapid characterization of various polyalphaolefin samples was reported using ASAP coupled with ion mobility spectrometry -mass spectrometry (IMS-MS).…”

Poly(ethylene glycol) Hydrogel Crosslinking Chemistries Identified via Atmospheric Solids Analysis Probe Mass Spectrometry

“…Compared to conventional pyrolysis probes, the ASAP source is operated at relatively low temperatures (≤500 °C), yielding not only monomeric but also oligomeric species that provide molecular connectivity detail. Further microstructural verification and complementary information on the thermal stability and degradation pathways of the polymer can be gained by tandem mass spectrometry (MS/MS) experiments. − In the past 13 years, ASAP-MS and ASAP-MS/MS have been used extensively to characterize polymer additives as well as diverse, relatively low molecular weight synthetic polymers, − including PEG, polystyrene, PU, and PDMS . An ASAP source combined with ion mobility (IM)-MS adds potential to separate desorbate and degradant ions by their size and shape, − thus enhancing the analytical information obtainable from mild thermal degradation experiments. − The added IM dimension enables the separation of isobaric and isomeric species and also permits determination of their collision cross-section (CCS) values, which provide a quantitative insight about their 3D size/shape.…”

“…39−41 In the past 13 years, ASAP-MS and ASAP-MS/MS have been used extensively to characterize polymer additives as well as diverse, relatively low molecular weight synthetic polymers, 44−48 including PEG, 45 polystyrene, 45 PU, 47 and PDMS. 48 An ASAP source combined with ion mobility (IM)-MS adds potential to separate desorbate and degradant ions by their size and shape, 49−51 thus enhancing the analytical information obtainable from mild thermal degradation experiments. 52−57 The added IM dimension enables the separation of isobaric and isomeric species and also permits determination of their collision cross-section (CCS) values, which provide a quantitative insight about their 3D size/shape.…”