Applications of FABMS

The group of compounds amenable to FABMS analysis is similar to that analysed by FD that is non-volatile polar sohds, however, FAB is more suited to high molecular weight very polar sohds and FD to compounds of lower polarity. The characteristic feature of FABMS spectra is the presence of intense [M -t-H]+ ion in addition to considerable number of characteristic fragment ions that are useful for structure analysis. 

In addition to molecvdar weight information. Fast Atom Bombardment Mass Spectrometry can also be used for sequencing polypeptides and oHgonucleotides. One such example is the study of the amino acid sequence in the ohgopeptide Antiamoebin I by Taylor et al. (30) by a combination of FAB and B/E-hnked scans. This peptide contains 16 amino acids. The peak at m/z 1670 is the quasi-molecular ion [M -t HF. A linked-scan experiment of the B/E type performed on this ion produced a peak at m/z 1422 which presented confirmatory evidence a loss of the terminal prohne.phenylalaninol.H group. A similar B/E scan from the latter ion produces ions at m/z 1337 and m/z 1244 for the loss of aminobutyric acid and hydroxyprohne.amino-isobutyric acid, respectively. This process can be repeated vmtil aU the amino acids are 

The main advantage of MS/MS is its abihty to analyse specific target molecules directly from biological matrices without any sample preparation. One important application of MS/MS in food analysis can be the rapid screening of intact fruits or vegetables for the presence of mycotoxins or pesticides. For example intact lettuce leaves can be introduced directly into the ion source and analysed for the presence of the pesticide parathion. The CAD (methane gas) spectrum of this pesticide shows the parent ion at m/z 291 and two daughter ions at m/z 169 and m/z 154. If the peak at m/z 291 of the normal spectrum of the contaminated lettuce leaf is selected and its CAD spectrum is recorded and 

Further Examples of Applications of Mass Spectrometry in Food Science 

Similar results can be obtained by operating double-focusing magnetic sector instruments in the B/E - linked scan mode. In this mode, the ratio of B to E is kept constant as B is scanned. The residting spectrum contains fragment ions from a selected precursor ion. Warburton et al. [31] used the B/E - hnked scan mode to show that the peak at m/z 210 in the lemon juice corresponds to citric acid, and the m/z 369 peak in the egg yolk is due to cholesterol. In our laboratories we have used the same technique to elucidate the mechanism of B-carboline formation in food from tryptophan Amadori product and the mechanism of pyrrole formation from lysine Amadori products [32, 33]. 

---