| Abstract: | Cs⁺ ion desorption is use to evaluate the potential use of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR) for the analysis of large biomolecules. FT-ICR is mechanically simple and capable of performing analysis on large (> 10,000 daltons) non-volatile/thermally labile molecules. The basic instrumental features of FT-ICR, e.g., mass range, high mass resolution, variability of operation parameters via computer, and operating speed, make FT-ICR a very attractive analytical spectrometer. It is demonstrated that the Cs⁺ beam fluence greatly effects the nature of the secondary ions; low beam fluence favors formation of [M+H]⁺ and/or [M+Na]⁺ ions, and high beam fluence favors formation of [M+xNa-(x-1)H)]⁺ and/or low mass fragment ions. A secondary result of these studies relates to the structural information that can be obtained by examining the dissociation reactions of the [M+H]⁺ and [M+xNa-(x-1)H]⁺ and/or low mass fragment ions. That is, these two ions fragment by different pathways and comparing the two mass spectra gives complementary structural information. It is clear from these studies that the dissociation dynamics of [M+Na]⁺ ions are controlled by the relative binding energies of H⁺ and Na⁺ to the molecule. The studies on the Cs⁺ ion DI-FT-ICR spectra of CsI demonstrate the high mass capabilities of the method. In addition, the studies demonstrated that ion ejection methods can be employed to increase the dynamic range of FT-ICR; however, if ion ejection is not performed properly collision-induced dissociation of high mass ions occurs. Thus, ion ejection must be used with some caution. The results of the studies presented serve to define the general operating parameters for preforming desorption ionization of large molecules by Cs⁺ DI-FT-ICR. |
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