Consecutive Infrared Multiphoton Dissociations in a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer

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Abstract
Consecutive infrared multiphoton dissociations (IRMPD) may be observed in a Fourier transform ion cyclotron resonance mass spectrometer (FTICR). This is the IRMPD equivalent of previous MSn experiments using CID. This work presents a versatile technique, using a bistable shutter to gate ON and OFF a continuous-wave (CW) CO2 laser for multiple irradiation periods of 0.1−1000 s duration. Consecutive photodissociations, up to MS4, are demonstrated for the proton-bound dimer of diethyl ether and the resulting fragment ions. The photoproducts are formed close to the center of the FTICR cell, resulting in high product ion recovery efficiency. This differs from CID products, which are formed throughout the FTICR cell causing reisolation/detection problems. The fragmentation resulting from the use of low-intensity, CW, infrared laser radiation is shown to be much more energy selective than CID. Photodissociation of C2H5OH2+ ion produces the lowest energy product ion exclusively, even though the two product channels differ only by ∼5 kcal/mol. Low-energy CID, however, produces a mixture of C2H5+ and H3O+ products in the ratio of 1.3:1. Hence, the higher energy pathway (C2H5+) is substantially favored. The current results indicate that this IRMPD MSn technique may be successfully applied to large biomolecules prepared by electrospray or MALDI.

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