Infrared-multiphoton dissociation

Note CID can rather easily be implemented on FT-ICR instmments because it only demands for a pulse valve and a reservoir. Although the collision gas in SORI-CID can be easily handled, its use is nonetheless in contradiction to the high vacuum requirements of the ICR cell. Thus, alternative ion activation techniques without the use of gas are desirable. 

The energy received from multiple photon absorption may also be used to activate and dissociate otherwise stable gaseous ions [135]  

Infrared multiphoton dissociation (IRMPD) was first described along with the dissociation of weakly bound protonated diethylether cluster ions [135]  

Note For IRMPD, care must be taken to block the IR laser from abandoning its assigned optical path. The IR laser is extremely powerful and can instantaneously ignite objects or cause injuries from bums. 

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The activation step can alternatively be performed without gas by means of infrared multiphoton dissociation (IRMPD) or electron capture dissociation (BCD) (Chap. 2.12.2). Both IRMPD and BCD, solely require storage of the ions during their excitation by photons or electrons, respectively. It is one of the most charming properties of FT-ICR-MS/MS that even the accurate mass of the fragment ions can be determined. [216,217]... 

Hashimoto, Y. Hasegawa, H. Yoshi-nari, K. Collision-Activated Infrared Multiphoton Dissociation in a Quadrapole Ion Trap Mass Spectrometer. Anal. Chem. 2003, 75,420-425. 

Gauthier, J.W. Trautman, T.R. Jacobson, D.B. Sustained Off-Resonance Irradiation for Collision-Activated Dissociation Involving FT-ICR-MS. CID Technique That Emulates Infrared Multiphoton Dissociation. Anal. Chim. Acta 1991,246,211-225. 

Hofstadler, S.A. Griffey, R.H. Pasa-Tolic, R. Smith, R.D. The Use of a Stable Internal Mass Standard for Accurate Mass Measurements of Oligonucleotide Fragment Ions Using ESI Fourier Transform Ion Cyclotron Resonance-MS With Infrared Multiphoton Dissociation. Rapid Commun. Mass Spectrom. 1998,12, 1400-1404. 

Minkwitz and Schneider54 have been able to obtain protonated methanol in the form of hexafluorometalate salts (MeOH2+MF6, M = As, Sb), and these were characterized by X-ray diffraction. Protonated propanol and proton-bound dimers of methanol, ethanol, and propanol with the proton shared between two alcohol molecules (5) have also been characterized by infrared multiphoton dissociation... 

FT-ICR instruments are also capable of performing MS" experiments. The most popular method of ion activation is sustained off-resonance irradiation (SORI), where ions are excited to a larger cyclotron radius using rf energy, undergo collisions with a neutral gas pulsed into the cell and dissociate. Other methods are available, including infrared multiphoton dissociation (IRMPD)65 and electron capture dissociation (ECD)66 which is of particular value in glyco-peptide analysis (Section VIA). 

K. Hakansson, H. J. Cooper, M. R. Emmett, C. E. Costello, A. G. Marshall, and C. L. Nilsson, Electron capture dissociation and infrared multiphoton dissociation MS/MS of an N-glycosylated tryptic peptide to yield complementary sequence information, Anal. Chem., 73 (2001) 4530-4536. 

Structural information on ions produced by laser desorption has also been obtained by using infrared multiphoton dissociation processes (73). A pulsed C02 laser was used to form the ions, which were further fragmented either by using sequential pulses from the same laser or by using a gated continuous wave infrared laser. 

Infrared Multiphoton Dissociation of Laser-Desorbed Ions... 

Output from both gated continuous wave and pulsed carbon dioxide lasers has been used to desorb ions from surfaces and then to photodissociate them in a Fourier transform ion cyclotron resonance mass spectrometer. Pulsed C02 laser irradiation was most successful in laser desorption experiments, while a gated continuous wave laser was used for a majority of the successful infrared multiphoton dissociation studies. Fragmentation of ions with m/z values in the range of 400-1500 daltons was induced by infrared multiphoton dissociation. Such photodissociation was successfully coupled with laser desorption for several different classes of compounds. Either two sequential pulses from a pulsed carbon dioxide laser (one for desorption and one for dissociation), or one desorption pulse followed by gated continuous wave irradiation to bring about dissociation was used. 

This is the highest molecular weight compound for which infrared multiphoton dissociation has been observed in our laboratories to date. A similar pathway was indicated by the collision-induced dissociation spectrum of this ion. Limited CID experiments were performed on some of the other laser-desorbed ions discussed here and in general the CID and PD pathways were the same. 

ESI mass spectra after the addition of 49 (or 50) to 51(PF6)2 show the hexameric clusters 51 (49)6 and 51 (50)6 as the dominating signals (Figure 3.24). These ions were irradiated in an infrared multiphoton dissociation experiment (I RMPD) with IR radiation from a C02 laser at different time intervals. The observed fragmentation behavior was exactly that expected for the hexameric capsule. 

Gauthier, J.W., Trautman, T.R. and Jacobson, D.B. (1991) Sustained off-resonance irradiation for collision-activated dissociation involving Fourier transform mass spectrometry. Collision-activated dissociation technique that emulates infrared multiphoton dissociation. 

Two other ion activation methods were developed to replace the gas molecules as targets by laser beams (photodissociation or infrared multiphoton dissociation IRMPD) or by electron beams (electron capture dissociation ECD). These two methods can be applied to ions that are trapped during their excitations by photons or electrons, respectively. Thus, they are most often used with ion trap or ICR analysers because the residence time and the interaction time are longer. 

The fragmentation of peptides can also be obtained by FTICR instruments. Besides the most commonly used activation method, namely CID, the activation can alternatively be performed without gas by infrared multiphoton dissociation (IRMPD) and electron capture dissociation (ECD). These methods fragment peptide ions in the ICR cell by emitting a laser beam or electron beam, respectively. 

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