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To trap or transmit, that is the question . . . trap (Q3) and measured. This method to apply to the particular elements of a The ability to fragment peptides and use can be implemented on a quadrupolehybrid quadrupole LIT to permit the ion dissociation information to search a TOF hybrid mass spectrometer as well as storage of ions of one polarity in a protein sequence database is at the core a LIT. For users of a mass spectrometer quadrupole cell and the transmission of of proteomics analyses. Initially, dissociawith two LITs (such as the Q TRAP), ions of the opposite polarity through tion was carried out through energy the reagents may be trapped transfer via collisions of ions with Analyte ions End lens End lens Anions and the peptides transmitted; an inert gas, that is, collision-inLIT this is the third method in the duced dissociation (CID). More (a) Passing Passing paper. In this case, the generatrecently, Donald Hunt and coed fragment ions are also transworkers at the University of Virmitted, so they must subseginia developed electron transfer (b) quently be stored in the second dissociation (ETD), which preTrapping Passing LIT and then mass analyzed. serves posttranslational modifiWhat are the differences becations on the peptides after dc tween the mutual-storage and fragmentation. (c) the trap-and-transmit meth3D quadrupole ion traps Trapping Passing ods? Not much, according to have been used primarily for McLuckey. In the mutual-stormutual storage of the ETD dc age mode, the reagent anions reagent and peptide ions. How(d) are thermalized, whereas their ever, pairing ETD with a linear Trapping Trapping energy is higher in transmission ion trap (LIT) has been probmode. The high energy sets a lematic because ions are only rf cutoff of ~12 eV for anion intrapped in two dimensions. Analyte ions (positively charged) Anions Background gas, N2 jection. Above the cutoff, colliChanges to the vacuum system sional cross sections decrease and hardware of LITs can help, so much that the ion–ion reac(a–d) Four ways of reacting reagent anions and peptide cations but this “fix” may be beyond tion efficiency plummets. The in a LIT generate effective peptide dissociation. the capabilities of most progroup found that it was importeomics labs. In this issue of the cell. McLuckey cautions that the tant to focus the two ion populations Analytical Chemistry (pp 3363–3370), Scott McLuckey and co-workers at Pur- trick is being able to control the voltage on the central axis of the linear trap and on each element in the system indethat ETD worked much better at the due University describe some easy-topendently. higher pressures found in Q2 (1–10 implement alterations that will allow The concept is straightforward. With mTorr) than at the lower pressures in researchers who have a tandem beama dual spray interface, peptide analyte Q3. They also observed some potential type mass spectrometer with a colliions are generated by ESI, and reagent CID effects (limited loss of a phosphate sion cell to perform ETD. With these anions (in this case, azobenzene) are group) from cation injection into the changes, there's no need to purchase generated by atmospheric-pressure pressurized Q2 cell. At the end of the new instrumentation or carry out exchemical ionization. Unlike previous efday, however, the two modes of operatensive modifications. forts, which introduced reagent ions ration appeared to provide virtually indis“The important evolutionary step dially into the cell, McLuckey and coltinguishable results. here,” explains McLuckey, “is to use “Generating new knowledge is one multiple sources with the same vacuum- leagues use axial introduction; this provides a more stable beam of well-con- of the most sublime things one can do,” chamber interface. The only hardware trolled anions. The current paper discuss- says McLuckey. With a few relatively modification you need to make is the es four approaches. In the second one, addition of an emitter.” In a series of simple modifications and some fine-tunanalytes are sprayed and trapped in the papers over the past 2 years, McLucking of the software controls, an array of collision quadrupole (Q2); then, the ey’s group has published the results of new research possibilities can be opened source is switched, and reagents are their efforts to create a way to introup for resourceful investigators with a sprayed and transmitted for ~80 millisec- tandem beam mass spectrometer and a duce reagent anions into a collision cell onds. The analytes and the fragments and get them to react with protonated quadrupole collision cell. Being sublime generated by the ion–ion interactions are has never been easier. a peptide ions. The current paper provides details on the sequence of voltages subsequently ejected into the linear ion —Karen R. Jonscher M A Y 1 , 2 0 0 7 / A N A LY T I C A L C H E M I S T R Y
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