In this letter, the authors would like to present a rapid method for mass-scale calibration of metastable dissociation in an orthogonal-axis time-of-flight instrument. The calibrating ion is a protonated polyhedral oligomeric silsesquioxane (POSS) generated in electrospray ionization. In addition, dissociation mechanisms for protonated POSS are proposed. Finally, the interest of the method is illustrated in the context of a collision-induced dissociation investigation of a sodium-cationized polylactide.
GoffinA.-L.DuquesneE.MoinsS.AlexandreM.DuboisP., “New organic–inorganic nanohybrids via ring opening polymerization of (di)lactones initiated by functionalized polyhedral oligomeric silsesquioxane”, Eur. Polym J.43, 4103 (2007). doi: 10.1016/j.eurpolymj.2007.07.041
2.
ZhaoY.Q.SchiraldiD.A., “Thermal and mechanical properties of polyhedral oligomeric silsesquioxane (POSS)/polycarbonate composites”, Polymer46, 11640 (2005).
3.
BourbigotS.DuquesneS.JamaC., “Polymer nanocomposites: How to reach low flammability?”, Macromol. Symp.233, 180 (2006). doi: 10.1002/masy.200690016
4.
MatejkaL.StrachotaA.PlestilJ.WhelanP.SteinhartM.SloufM., “Epoxy networks reinforced with polyhedral oligomeric silsesquioxanes (POSS). Structure and morphology”, Macromolecules37, 9449 (2004). doi: 10.1021/ma0484577
5.
Aminopropylheptakis(isobutyl)POSS (POSS-NH2, 97%) was purchased from Hybrid Plastics.
6.
All experiments were performed on a Waters QToF2 mass spectrometer. The analyte solutions were delivered to the ESI source by a Harvard Apparatus syringe pump at a flow rate of 5 μL min−1. Typical ESI conditions were: Capillary voltage, 3.1 kV; cone voltage, 15 V; source temperature, 80°C; desolvation temperature, 120°C. Dry nitrogen was used as the ESI gas. For the recording of the single-stage ESI-MS spectra, the quadrupole (rf-only mode) was set to pass ions from 50 Th to 1000 Th, and all ions were transmitted into the pusher region of the time-of-flight analyzer where they were mass analyzed with 1 s integration time. Data were acquired in continuum mode until acceptable averaged data were obtained. For the ESI-MS/MS CID experiments, the ions of interest are mass-selected by the quadrupole mass filter. The precursor ion resolution is adjusted to select only the monoisotopic signal amongst the complete isotopic cluster. The selected ions are then submitted to collision against argon in the rf-only hexapole collision cell. All ions coming out of the hexapole cell, either the fragments or the non dissociated precursor ions, are finally mass-measured with the oa-ToF analyzer.
7.
NavenT.J.P.HarveyD.J.BrownJ.CritchleyG., “Fragmentation of complex carbohydrates following ionization by matrix-assisted laser desorption with an instrument fitted with time-lag focusing”, Rapid Commun. Mass Spectrom.11, 1681 (1997). doi: 10.1002/(SICI)1097-0231(19971015)11:15<1681::AID-RCM34>3.0.CO;2-0
8.
BrownR.S.LennonJ.J., “Sequence-specific fragmentation of matrix-assisted laser-desorbed protein peptide ions”, Anal. Chem.67, 3990 (1995). doi: 10.1021/ac00117a027
9.
KaufmannR.SpenglerB.LutzenkirchenF., “Mass-spectrometric sequencing of linear peptides by product-ion analysis in a reflectron time-of-flight massspectrometer using matrix-assisted laser-desorption ionization”, Rapid Commun. Mass Spectrom.7, 702 (1993). doi: 10.1002/rcm.1290071010
10.
CooksR.G.BeynonJ.H.CaprioliR.M.LesterG.R., Metastable Ions.Elsevier Scientific Publishing Company, Amsterdam, The Netherlands (1973).
11.
HarveyD.J.HunterA.P.BatemanR.H.BrownJ.CritchleyG., “Relationship between in-source and post-source fragment ions in the matrix-assisted laser desorption (ionization) mass spectra of carbohydrates recorded with reflectron time-of-flight mass spectrometers”, Int. J. Mass Spectrom.188, 131 (1999). doi: 10.1016/S1387-3806(99)00014-7
12.
VersluisC.Van der StaaijA.StokvisE.HeckA.J.R.De CraeneB., “Metastable ion formation and disparate charge separation in the gas-phase dissection of protein assemblies studied by orthogonal time-of-flight mass spectrometry”, J. Am. Soc. Mass Spectrom.12, 329 (2001). doi: 10.1016/S1044-0305(00)00227-0
13.
TuyttenR.LemièreF.Van DongenW.EsmansE.L.WittersE.HerreboutW.Van Der VekenB.DudleyE.NewtonR.P., “Intriguing mass spectrometric behavior of guanosine under low energy collision-induced dissociation: H2O adduct formation and gas-phase reactions in the collision cell”, J. Am. Soc. Mass Spectrom.16, 1291 (2005). doi: 10.1016/j.jasms.2005.03.026
14.
ColletteC.De PauwE., “Calibration of the internal energy distribution of ions produced by electrospray”, Rapid Commun. Mass Spectrom.12, 165 (1998). doi: 10.1002/(SICI)1097-0231(19980227)12:4<165::AID-RCM140>3.0.CO;2-1
15.
In a glovebox, 0.06 g (nNH2 = 2.5 10−4 mol) of hexadecylamine and 0.36 g (nLA = 2.5 10−3 mol) of dried L-lactide were introduced by the glove box in a previousely flamed and nitrogen purged two-neck flask equipped with a three-way stopcock and a magnetic stirring bar. Outside of the box, the L-lactide/hexadecylamine mixture was charged successively by toluene (4 mL) and tin (II) octoate [Sn(Oct)2; 1 mL of a 0.1 M toluene solution] under nitrogen by using previously flame-dried syringes. The mixture was then heated at 75°C under stirring. After 20 h, the polymerization was stopped by adding a few drops of diluted hydrochloric acid (1 M). The obtained polymer was then precipitated out from cold heptane, filtered and dried under vacuum at 40°C. 1H-NMR [300 MHz, CDCl3, δ (ppm)]: 0.8–1(t, 3H), 1.3 (s, 28H), 1.5–1.9 (d, 3(2n + 1)H), 3.8 (m, 2H), 4.4 (q, 1H; CH–OH), 5–5.3 (q, 2nH), 6.2 (1H; NH).
16.
OsakaI.WatanabeM.TakamaM.MurakamiM.ArakawaR., “Characterization of linear and cyclic polylactic acids and their solvolys products by electrospray ionization mass spectrometry”, J. Mass. Spectrom.41, 1369 (2006). doi: 10.1002/jms.1110
17.
AdamusG., “Structural analysis of poly[(R,S)-3-hydroxybutyrate-co-L-lactide] copolyesters by electrospray ionization ion trap mass spectrometry”, Rapid Commun. Mass Spectrom.21, 2477 (2007). doi: 10.1002/rcm.3111
18.
De WinterJ.CoulembierO.MarsalP.CornilJ.DuboisP.GerbauxP., in preparation.
