Negative Nucleotide Ions as Sensitive Probes for Energy Specificity in Collision Induced Fragmentation in Mass Spectrometry.

RATIONALE: The most commonly used fragmentation methods in tandem MS are CID and HCD. While in CID, the preselected ions in the trap are resonantly (and m/z exclusively) excited, in HCD the entire m/z range experiences the dissociative acceleration. The different excitation is reflected in different fragment distributions.

METHODS: As a test-bed for particularly pronounced fragmentation specificity, here MS/MS experiments on several 4-mer oligonucleotides were conducted employing both collision methods and the results were thoroughly compared. Oligonucleotides are shown to be sensitive probe to subtle changes, especially in the negative ion mode. A detailed analysis of these differences reveals insight into the dissociation mechanics.

RESULTS: The differences are represented in heat-maps, which allow for a direct visual inspection of large amounts of data. In these false colour representations the, sometimes subtle, changes in the individual dissociation product distributions become distinct. Another advantage of these graphic plots can be found in the formation of systematic patterns. These patterns reflect trends in dissociation specificity which allow for the formulation of general rules in fragmentation behavior.

CONCLUSIONS: Instruments equipped with two different excitation schemes for tandem MS are today widely available. Nonetheless, direct comparisons between the individual results are scarcely made. Such comparative studies bear a powerful analytical potential to elucidate fragmentation reaction mechanism.