Negative fast atom bombardment

H. Y. Lin, G. Gonyea, S. Killeen, and S. K. Chowdhury. Negative Fast Atom Bombardment Ionization of Aromatic Sulfonic Acids Unusual Sample-Matrix Interaction. Rapid Commun. Mass Spectrom., 14(2000) 520-522. 

Holzmann and Leuckert (1990) applied the methods of negative Fast Atom Bombardment... 

Holzmann G, Leuckert C (1990) Applications of negative fast atom bombardment and MS/MS to screening of lichen compounds. Phytochemistry 29 2277-2283... 

A big step forward came with the discovery that bombardment of a liquid target surface by abeam of fast atoms caused continuous desorption of ions that were characteristic of the liquid. Where this liquid consisted of a sample substance dissolved in a solvent of low volatility (a matrix), both positive and negative molecular or quasi-molecular ions characteristic of the sample were produced. The process quickly became known by the acronym FAB (fast-atom bombardment) and for its then-fabulous results on substances that had hitherto proved intractable. Later, it was found that a primary incident beam of fast ions could be used instead, and a more generally descriptive term, LSIMS (liquid secondary ion mass spectrometry) has come into use. However, note that purists still regard and refer to both FAB and LSIMS as simply facets of the original SIMS. In practice, any of the acronyms can be used, but FAB and LSIMS are more descriptive when referring to the primary atom or ion beam. 

An abundant molecular ion may indicate that an aromatic compound or highly unsaturated ring compound is present. If no molecular ion is observed and one cannot be deduced, the use of chemical ionization (ci), negative chemical ionization (nci), fast atom bombardment (FAB), or electrospray ionization (ESI) should provide a molecular ion. 

Mass Spectrometry. Mass spectrometry holds great promise for low-level toxin detection. Previous studies employed electron impact (El), desorption chemical ionization (DCI), fast atom bombardment (FAB), and cesium ion liquid secondary ion mass spectrometry (LSIMS) to generate positive or negative ion mass spectra (15-17, 21-23). Firm detection limits have yet to be reported for the brevetoxins. Preliminary results from our laboratory demonstrated that levels as low as 500 ng PbTx-2 or PbTx-3 were detected by using ammonia DCI and scans of 500-1000 amu (unpublished data). We expect significant improvement by manipulation of the DCI conditions and selected monitoring of the molecular ion or the ammonia adduction. 

More recently, attention has turned to the aftertreatment of commercially available mordant dyes on wool with iron(II) and iron(III) salts as a potential source reduction approach to eliminating chromium ions from dyebath effluent [34]- The anticipated improvements in fastness performance were achieved. The structures of the conventional 1 2 iron-dye complexes formed on the wool fibres were characterised by negative-ion fast-atom bombardment spectroscopy and HPLC analysis [35]. 

While fast atom bombardment (FAB) [66] and TSI [25] built up the basis for a substance-specific analysis of the low-volatile surfactants within the late 1980s and early 1990s, these techniques nowadays have been replaced successfully by the API methods [22], ESI and APCI, and matrix assisted laser desorption ionisation (MALDI). In the analyses of anionic surfactants, the negative ionisation mode can be applied in FIA-MS and LC-MS providing a more selective determination for these types of compounds than other analytical approaches. Application of positive ionisation to anionics of ethoxylate type compounds led to the abstraction of the anionic moiety in the molecule while the alkyl or alkylaryl ethoxylate moiety is ionised in the form of AE or APEO ions. Identification of most anionic surfactants by MS-MS was observed to be more complicated than the identification of non-ionic surfactants. Product ion spectra often suffer from a reduced number of negative product ions and, in addition, product ions that are observed are less characteristic than positively generated product ions of non-ionics. The most important obstacle in the identification and quantification of surfactants and their metabolites, however, is the lack of commercially available standards. The problems with identification will be aggravated by an absence of universally applicable product ion libraries. 

Example Cesium iodide is frequently used for mass calibration in fast atom bombardment (FAB) mass spectrometry (Chap. 9) because it yields cluster ions of the general formula [Cs(CsI)n] in positive-ion and [I(CsI)J in negative-ion mode. For the [Cs(CsI)io] cluster ion, m/z 2730.9 is calculated instead of the correct value m/z 2731.00405 by using only one decimal place instead of the exact values Mi33Cs = 132.905447 and M1271 = 126.904468. T e error of 0.104 u is acceptable for LR work, but definitely not acceptable if accurate mass measurements have to be performed. 

Aubagnac, J.-L. Use of M-Nitrobenzyl Alcohol As a Matrix in Fast-Atom-Bombardment Negative-Ion Mass Spectrometry of Polar Compounds. Rapid Commun. Mass Spectrom. 1990, 4, 114-116. 

Figure 3. Positive (upper) and negative (lower) mass spectra of TTX, as measured by fast atom bombardment mass spectrometry.

When optically inactive polystyrene was used as adsorbent, no difference in the relative peak intensity at m/z 288 to 286 was detected. Moreover, in the resolution of (RS)-1,1 -bi-2-naphthol and (if5)-l,l,-bi-2-naphthol-rf2 on the CSP, no isotope effect was observed. These findings indicate that the difference in EI-MS spectra is due to the difference in desorption between the enantiomers from the chiral adsorbent tris(5-f uoro-2-methylphenylcarbamate). This method can be used to discriminate the chirality of other enantiomers of small molecules if they show peaks in their EI-MS spectra in the presence of chiral polymers. Similar chiral recognition was detected by negative ion fast-atom bombardment mass spectrometry [34],... 

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