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Tandem mass spectrometry represents an important analytical tool to unravel molecular structures and to study the gas-phase behavior of organic molecules. Besides commonly used methods like collision-induced dissociation and electron capture or transfer dissociation, new ultraviolet light–based techniques have the potential to synergistically add to the activation methods. Here, we present a new simple, yet robust, experimental design for polychromatic activation of trapped ions using the 115–160 nm output of a commercially available deuterium lamp. The resulting continuous dissociative excitation with photons of a wide energy range from 7.7 to 10.8 eV is studied for a comprehensive set of analyte classes in both positive and negative ion modes. While being simple, affordable, compact, and of low maintenance, the new setup initiates fragmentation of most precursor ions via their known dissociation pathways. Additionally, some new fragmentation patterns were discovered. Especially, electron loss and electron capture reactions with subsequent fragmentations were observed. For oligonucleotides, peptides, carbohydrates, and organic dyes, in comparison to collision-induced dissociation, a significantly wider fragment distribution was obtained, resulting in an information increase. Since the individual photons carry enough energy to post-ionize the nascent fragments, a permanent vacuum ultraviolet light exposure inside the ion trap potentially goes along with a general increase in detection capability.
Tandem MS techniques are widely used for both, structure and sequence elucidation of biopolymers. Thereby, fragmentation activation is realized by various methods, for example with lasers or collisions with neutral gases. In this study, we present a new Tandem MS system using a commercially available vacuum ultraviolet lamp. On the one hand, this approach provides efficient fragmentation in both ionization modes, positive as well as negative. On the other hand, it enables an additional previously not achieved post ionization of the fragments. While the first results in atypical fragment patterns and, thus provides orthogonal information, the second is crucial especially to identify low abundant ions.
Tandem MS techniques are widely used for both, structure and sequence elucidation of biopolymers. Thereby, fragmentation activation is realized by various methods, for example with lasers or collisions with neutral gases. In this study, we present a new Tandem MS System using a commercially available vacuum ultraviolet lamp. On the one hand, this approach provides efficient fragmentation in both ionization modes, positive as well as negative. On the other hand, it enables an additional previously not achieved post ionization of the fragments. While the first results in atypical fragment patterns and, thus provides orthogonal information, the second is crucial especially to identify low abundant ions.
Rationale: The most commonly used fragmentation methods in tandem mass spectrometry (MS/MS) are collision‐induced dissociation (CID) and higher energy collisional dissociation (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 probes to subtle changes, especially in the negative ion mode. A detailed analysis of these differences reveals insight into the dissociation mechanics. Results: Thedifferencesarerepresentedinheat‐maps,whichallowforadirectvisualinspection oflargeamountsofdata.Inthesefalsecolourrepresentationsthe,sometimessubtle,changesinthe 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 MS/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.
Multiply negatively charged DNA oligonucleotides of small sizes (n=15-40 bases) have been subjected to a comprehensive tandem mass spectrometric study (MS/MS). Collision induced dissociation (CID) mass spectrometry (MS) was applied as a tool to break down isolated DNA oligonucleotides with a defined number of charges. Various lenghts and sequences were analyzed unravelling a comparable direct correlation between the threshold collision energy for fragmentation and the charge-per-base density in the precusor ion. It was also revealed that the increase in charges and thus Coulomb repulsion results in the transition from a folded, compact form to an elongated structure of the precusor ions.
Tandem MS experiments allow the fast acquisition of spectral datasets with enormous size and unprecedented content of information. The most commonly used method is undoubtedly collision induced dissociation (CID). The relatively young technical adaptation of CID to modern day Orbitrap experiments needs a higher confinement voltage and has accordingly been named higher-energy collisional dissociation HCD. Despite the name the absolute value of transferred energy per collision in HCD is lower than in CID. Since for many proteins CID and HCD result in comparable fragmentation patterns the two techniques are often treated as interchangeable. This approach is, however, not without pitfalls as other classes of biomolecules often exhibit strongly pronounced fragmentation specificity. As an example, MS/MS experiments on several 4-mer oligonucleotides were conducted employing both collision methods and the results were thoroughly compared. It is apparent that not only the total fragment yield but also the identity of the observed fragments differ significantly between the two methods.