Hard ionization

ICP is an atmospheric pressure ionization method. However, unlike most atmospheric pressure ionization methods, which are soft (i.e., producing little fragmentation), ICP is the ultimate in "hard ionization, typically leading to complete atomization of the sample during ionization. Consequently, its primary use is for elemental analysis. In the... 

One of the early methods for mass spectrometric analysis of microdialysis samples utilized gas chromatography with mass spectrometric detection (GC/MS). Electron ionization is one type of ionization used for GC/MS. It is a hard ionization technique, resulting in a high degree of analyte fragmentation. A softer form of ionization, chemical ionization, is also available and often results in less analyte fragmentation. Selected-ion monitoring (SIM) is used frequently with... 

Hardness and softness of ionization refer to the energetics of forming an ion from a neutral molecule and the extent of spontaneous fragmentation resulting from the ionization process. Hard ionization techniques induce extensive fragmentation. Soft ionization techniques induce minimal or no fragmentation. 

FIGURE 20-2 Mass spectrum of 1 -decanol from (a) a hard ionization source (electron impact) and (b) a soft ionization source (chemical ionization),... 

What is the difference between hard ionization and soft ionization ... 

Chemical Potential, Hardness, Ionization Potential, and Electron Affinity. 33... 

TABLE 4.7 The Absolute Electronegativity Hardness Ionization Potential and Electron Affinity EA, Computed Upon the Eqs. (4.261), (4.259), (4.262) and (4.263), Respectively, for the Ordinary Elements... 

The fundamental issue of elemental periodicity is here addresses through quantitative-structure-property-relationship (QSPR) by assuming the atomic number as the atomic activity/property to be correlated with structural indicators, among which those relating with outermost orbitals, electronegativity, chemical hardness, ionization potential and electronic... 

Guo, Y., Whitehead, M. A. (1989). Application of generalized exchange local-spin-density-functional theory electronegativity, hardness, ionization potential, and electron afSnity. Phys. Rev. A 39,2317-2323. 

Soft ionization MS techniques [9] like electrospray ionization (ESI) and soft laser desorption, often known as matrix-assisted laser desorption/ioniza-tion (MALDI), facilitated the polymer analyses over the last years. The advantage of the soft ionization techniques is the transformation of dissolved liquid or solid sample into the gas phase, where no change in the molecular composition/structure of the sample will be induced, while hard ionization in mass spectrometry (e.g., electron ionization (El) or fast atom bombardment (FAB)) preferentially destroys the chemical and molecular structure into fragments prior to the detection of the molar mass fragments of the sample by mass spectrometry. 

Hard ionization, in particular electron ionization (Section 2.2.1), imparts more energy than that required for the formation of molecular ions. The distribution of the excess energy frequently causes the dissociation of bonds within the analyte molecules, resulting in extensive fragmentation. 

Figure 5. Soft(5a) and partial hard ionization(5b) mass spectra of the phenylthiohydantoine-tyrosine...

Figure 8. Partial hard ionization mass spectrum of leucine-enkephaline.

Both partial hard ionization mass spectra of these pentapeptides allow to detect the molecular ions as intense signals. It should be noted that in case of the leucine-enkephaline neither the C-terrainal nor the N-terminal end of the molecule is blocked. In case of the pentagastrine both ends are protected. Besides these molecular ion peaks several signals due to the breakdown of the peptide bond are detectable. 

Figure 11 displays the soft and the hard ionization mass spectra of the decapeptide angiotensin I. Again the soft ionization mass spectrum shows exclusively the molecular ion of this compound. The partial hard ionization mass spectrum shows mass patterns that permit the deduction of the peptide sequence. The main signals are due to the bond breaking around the carbonyl group of the peptide chain. The breakdown pattern of this compound is shown schematically in Figure 12. Only minor fragmentation occurs in the side chain.

Figure 11, Breakdown pattern and partial hard ionization mass spectrum angiotensin I.

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