Anal. Chem. 1999, 71, 3637-3641 Determination of End Groups of Synthetic Polymers by Matrix-Assisted Laser Desorption/ Ionization: High-Energy Collision-Induced Dissociation Andrew R. Bottrill, Anastassios E. Giannakopulos, Carl Waterson, David M. Haddleton, Ken S. Lee, and Peter J. Derrick* Institute of Mass Spectrometry and Department of Chemistry, University of Warwick, Coventry, CV4 7AL, United Kingdom Matrix-assisted laser desorption/ionization has been com- MALDI-time-of-flight (TOF) mass spectrometry to obtain values bined with high-energy collision-induced dissociation for for molecular mass averages, Mn and Mw, especially in combination the analysis of poly(ethylene glycols) with butanoyl, with size exclusion chromatography.17-20 benzoyl and acetyl end groups, using novel technology Techniques of polymer synthesis are becoming increasingly comprising a magnetic-sector mass spectrometer and ion sophisticated with a move toward the attempt to design macro- buncher with an in-line quadratic-field ion mirror. High- molecules for specific application. This has usually been centered energy (>8 keV) collision-induced dissociation facilitated around living, or pseudoliving, polymerization which allows the unambiguous end-group determination of these polymers, incorporation of different functionalities at precise positions by providing masses of end groups and structural informa- judicious choice of reaction conditions.28-34 For example, R and tion. The high-energy collision-induced dissociation also â terminally functional polymers may have very different proper- provided information regarding repeat units. (12) Williams, J. B.; Gusev, A. I.; Hercules, D. M. Macromolecules 1997, 30, 3781-3787. (13) Montaudo, G.; Montaudo, M. S.; Puglisi, C.; Samperi, F.; Sepulchre M. Mass spectrometry of synthetic polymers is gaining in popular- Macromol. Chem. Phys. 1996, 197, 2615-2625. (14) Zammit, M. D.; Davis, T. P.; Haddleton, D. M.; Suddaby, K. G. Macromol- ity due to the unprecedented high-quality information accessible ecules 1997, 30, 1915-1920. to the synthetic polymer chemist. Matrix-assisted laser desorp- (15) Guttman, C. M.; Blair, W. R.; Danis, P. O. J. Polym. Sci., Part B: Polym. tion/ionization (MALDI) has been shown to be an especially Phys. 1997, 35, 2409-2419. (16) Duncalf, D. J.; Wade, H. J.; Waterson, C.; Derrick, P. J.; Haddleton, D. M.; 1-8 useful tool for the direct analysis of synthetic polymers. The McCamley, A. Macromolecules 1996, 29, 6399-6403. results obtained for polymers from MALDI mass spectrometry (17) Nielen, M. W. F. Anal. Chem. 1998, 70, 1563-1568. experiments typically give qualitative molecular weight information (18) Montaudo, M. S.; Puglisi, C.; Samperi, F.; Montaudo, G. Rapid Commun. Mass Spectrom. 1998, 12, 519-528. but normally not structural information. Nevertheless, MALDI has (19) Jackson, C.; Larsen, B.; McEwen, C. Anal. Chem. 1996, 68, 1303-1308. been utilized to gain information on monomer reactivity ratios,9 (20) Kassis, C. E.; DeSimone, J. M.; Linton, R. W.; Lange, G. W.; Friedman, R. end groups,10-13 and mechanisms of polymerization.14-16 Many M. Rapid Commun. Mass Spectrom. 1997, 11, 1134-1138. (21) Barber, M.; Bordoli, R. S.; Sedgewick, R. D.; Tyler, A. N. Nature 1981, attempts, with a variety of success, have also been made to use 293, 270-275. (22) Arberth, W.; Straub, K. M.; Burlingame, A. L. Anal. Chem. 1982, 54, 2029- (1) Bahr, U.; Depe A.; Karas, M.; Hillenkamp, F.; Giessmann, U. Anal. Chem. 2034. 1992, 64, 2866-2869. (23) Craig, A. G.; Derrick, P. J. J. Chem. Soc., Chem. Commun. 1985, 891- (2) Belu, A. M.; DeSimone, J. M.; Linton, R. W.; Lange, G. W.; Friedman, R. 892. M. J. Am. Soc. Mass Spectrom. 1996, 7,11-24. (24) Craig, A. G.; Derrick, P. J. Aust. J. Chem. 1986, 39, 1421-1434. (3) Lloyd, P. M.; Suddaby, K. G.; Varney, J. V.; Scrivener, E.; Derrick, P. J.; (25) Jackson, A. T.; Jennings, K. R.; Scrivens, J. H. J. Am. Soc. Mass Spectrom. Haddleton, D. M. Eur. Mass Spectrom. 1995, 1, 293-300. 1997, 8,76-85. (4) Hoberg, A.-M.; Haddleton, D. M.; Derrick, P. J. Eur. Mass Spectrom. 1997, (26) Jackson, A. T.; Yates, H. T.; Scrivens, J. H.; Critchley, G.; Brown, J.; Green, 3, 471-473 M. R.; Bateman, R. H. Rapid Commun. Mass Spectrom. 1996, 10, 1668- (5) Creel, H. S. Trends Pol. Sci. 1993, 1, 336. 1674. (6) Jackson, C. A.; Simonsick, W. J. Curr. Opin. Solid. State Mater. Sci. 1997, (27) Andersen, U. N.; Colburn, A. W.; Makarov, A. A.; Raptakis, E. N.; Reynolds, 2, 661-667. D. J.; Derrick, P. J.; Davis, S. C.; Hoffman, A. D.; Thomson, S. Rev. Sci. (7) Danis, P. O.; Karr, D. E.; Simonsick, W. J.; Wu, D. T. Macromolecules 1995, Instrum. 1998, 69, 1650-1660. 28, 1229-1232. (28) Webster, O. W. Science 1991, 251, 887-893. (8) Danis, P. O.; Karr, D. E.; Xiong, Y.; Owens, K. G. Rapid Commun. Mass (29) Davis, T. P.; Haddleton, D. M.; Richards, S. N. J. Macromol. Sc., Rev. Spectrom. 1996, 10, 862-868. Macromol. Chem. Phys. 1994, C34, 243-324. (9) Suddaby, K. G.; Hunt, K. H.; Haddleton, D. M. Macromolecules 1996, 29, (30) Haddleton, D. M.; Waterson, C.; Derrick, P. J.; Jasieczek, C.; Shooter, A. J. 8642-8649. Chem. Commun. 1997, 683-684. (10) Maloney, D. R.; Hunt, K. H.; Lloyd, P. M.; Muir, A. V. G.; Richards, S. N.; (31) Matyjaszewski, K. J. Phys. Org. Chem. 1995, 8, 197-207. Derrick, P. J.; Haddleton, D. M. J. Chem. Soc., Chem. Commun. 1995, 561- (32) Yeates, S. G.; Richards, S. N. Surf. Coat. Int. 1996, 10, 437-442. 562. (33) Matyjaszewski, K.; Wang, J.-L.; Grimaud, T. J.; Shipp, D. A. Macromolecules (11) Montaudo, G.; Montaudo, M. S.; Puglisi, C.; Samperi, F. J. Pol. Sci. A Pol. 1998, 31, 1527-1534. Chem. 1996, 34, 439-447. (34) Perec, V.; Kim, H. J.; Barboiu, B. Macromolecules 1997, 30, 8526-8528. 10.1021/ac990523t CCC: $18.00 © 1999 American Chemical Society Analytical Chemistry, Vol. 71, No. 17, September 1, 1999 3637 Published on Web 07/24/1999 ties in certain applications. Thus it is important for techniques to be developed that can confirm, or refute, synthetically targeted macromolecular structures. In addition to empirical molecular mass data, it is important to be able to determine information regarding the end groups of and the sequence of monomers/ groups within a synthetic macromolecule. Tandem mass spec- trometry can in principle provide such structural information for a synthetic polymer. Tandem mass spectrometry has been widely used in the biological area, combined with ionization techniques such as liquid secondary ion mass spectrometry (LSIMS)21,22 and electrospray ionization. Early investigations with field desorption showed how tandem mass spectrometry could be used to investigate the structure of synthetic polymers.23,24 End-group information for poly(methyl methacrylate) (PMMA) has been derived from LSIMS using collision-induced dissociation (CID) at 4-keV collision energy in magnetic-sector instruments.25 The envelopes of peaks due to cationized molecules in these LSIMS experiments were centered at lower mass-to-charge ratios than the molecule-ion envelopes with MALDI for the same Figure 1. Structures of the differing end-terminated poly(ethylene polymers, presumably as a result of reduced ionization efficiency glycol) oligomers chosen for MALDI-CID. in the high-mass region in the LSIMS case. MALDI-CID results for poly(ethylene glycol)s (PEGs), MALDI-CID results for PMMA, possible full control over the laboratory-frame collision energy. and LSIMS-CID results for PMMAs have been reported by The expectation was that the high laboratory-frame collision (103- 4 Jackson et al.,26 utilizing laboratory collision energy of 800 eV on 10 eV) accessible in MAG-TOF would be advantageous as regards a magnetic-sector/orthogonal TOF instrument. For the PMMAs, fragmentation of large ions. The high laboratory-frame collision better signal-to-noise ratios were reported for the MALDI-CID energies access interaction times shorter than those accessible spectra compared to the LSIMS tandem mass spectra, due at least at lower energies. For example, center-of-mass collision energy in part to the higher sensitivities of MALDI. With orthogonal TOF, is approximately the same for a large ion at a laboratory-frame ion energies prior to orthogonal acceleration, and hence collision collision energy of 800 eV with Ar collision gas as at a laboratory- energies, need to be low (ideally <100 eV), and the 800-eV frame collision energy of 8000 eV with He collision gas. The collision energy employed in these experiments would be very physical processes differ, however, as is evidenced by the results much an upper limit. The restriction to low collision energies is presented in this paper, with one significant difference being the the major shortcoming of orthogonal TOF in the context of tandem interaction times. The results presented here are consistent with mass spectrometry. The novel instrument27 used in this study has the fragmentation induced by collision being more localized within E been designed to overcome any limitation or restriction of collision the macromolecule at the higher LAB's and shorter interaction times, when energy transfer must occur within a smaller time energy to low values (see below). window. In this paper, we report CID experiments with poly(ethylene glycol)s with different R, terminal functionalities performed using â EXPERIMENTAL SECTION novel hybrid magnetic-sector/time-of-flight instrumentation (MAG- Cationized molecules were produced using a MALDI ion 27 TOF). The instrumentation consisted of a Kratos Concept H source and accelerated to 8 keV at the ion source. Particular ions double-focusing magnetic sector and associated ion buncher as were selected for fragmentation by adjusting the magnetic field the first mass spectrometer (MS-1) and a planar hyperbolic (so- strength and exit slit in MS-1.