Mass spectrometry secondary structure

Ions are also used to initiate secondary ion mass spectrometry (SIMS) [ ], as described in section BI.25.3. In SIMS, the ions sputtered from the surface are measured with a mass spectrometer. SIMS provides an accurate measure of the surface composition with extremely good sensitivity. SIMS can be collected in the static mode in which the surface is only minimally disrupted, or in the dynamic mode in which material is removed so that the composition can be detemiined as a fiinction of depth below the surface. SIMS has also been used along with a shadow and blocking cone analysis as a probe of surface structure [70]. 

Sputtered Neutral Mass Spectrometry (SNMS) is the mass spectrometric analysis of sputtered atoms ejected from a solid surface by energetic ion bombardment. The sputtered atoms are ionized for mass spectrometric analysis by a mechanism separate from the sputtering atomization. As such, SNMS is complementary to Secondary Ion Mass Spectrometry (SIMS), which is the mass spectrometric analysis of sputtered ions, as distinct from sputtered atoms. The forte of SNMS analysis, compared to SIMS, is the accurate measurement of concentration depth profiles through chemically complex thin-film structures, including interfaces, with excellent depth resolution and to trace concentration levels. Genetically both SALI and GDMS are specific examples of SNMS. In this article we concentrate on post ionization only by electron impact. 

Further structural information is available from physical methods of surface analysis such as scanning electron microscopy (SEM), X-ray photoelectron or Auger electron spectroscopy (XPS), or secondary-ion mass spectrometry (SIMS), and transmission or reflectance IR and UV/VIS spectroscopy. The application of both electroanalytical and surface spectroscopic methods has been thoroughly reviewed and appropriate methods are given in most of the references of this chapter. 

Visible and UV spectrometry are of secondary importance to other spectral methods for the identification and structural analysis of unknown compounds. This is a direct consequence of the broad bands and rather simple spectra which make differentiation between structurally related compounds difficult. As an adjunct to infrared, magnetic resonance and mass spectrometry, however, they can play a useful role. They can be particularly helpful in confirming the presence of acidic or basic groups in a molecule from the changes in band position and intensity associated with changes in pH (p. 369). 

A. Benninghoven and W. K. Sichtermann. Detection, Identification, and Structural Investigation of Biologically Important Compounds by Secondary Ion Mass Spectrometry. Anal. Chem., 50(1978) 1180-1184. 

In secondary ion mass spectrometry (SIMS), a primary ion beam bombards the surface and a mass spectrometer analyses the ions sputtered from the surface by the primary bombardment. This extremely sensitive technique provides both elemental and structural information. 

Mass spectrometry is the method of choice for the structural characterization of secondary modifications. An overview over the diversity of this field is beyond the scope of this chapter and only the principal methods used are described. 

Richardson SD, Thruston AD, McGuire JM, Weber EJ (1993) Structural characterization of reactive dyes using liquid secondary ion mass spectrometry/tandem mass spectrometry. Environmental Protection Agency (EPA) Rep EPA600J93423, p 99... 

As shown by mass spectrometry and NMR spectroscopy, these amine derivatives of Cgfl, after work up, are dehydrogenated adducts [81]. After nucleophilic addition, the H atoms brought in by the diamines were oxidatively eliminated. The final adduct formation of the secondary diamines proceeds exclusively at [6,6] bonds. Besides the monoadduct, most of the regioisomeric bisadducts of piperazine or N,N -dimefhylethylenediamine and Cjq could be separated by column chromatography. The structure of the monoadduct and some of these bis-adducts were proven by X-ray crystal-structure analysis [90]. 

---