Tandem MS Experiments Research Articles

Time-of-flight mass spectrometry: State-of the-art in chemical analysis and molecular science.

Time-of-flight instruments form a well-established group of mass spectrometers, with its popularity still increasing. This article gives a survey of the technical basics and important instrumental developments in this field. Special notice is taken of factors that limit the mass resolution and to techniques to overcome them. The possibilities to perform tandem MS experiments in flight-time mass analyzers and their combination with ion-trapping devices are discussed. Finally, some examples of the modern applications of these instruments in molecular science and instrumental analysis are reviewed. © 1997 John Wiley & Sons, Inc.

Identification of Derivatized Peptides Without Radiolabels: Tandem Mass Spectrometric Localization of the Tagged Active-Site Nucleophiles of Two Cellulases and a β-Glucosidase

A new method that uses nonradioactive active site-directed enzyme inactivators and high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-ESIMS/MS) to identify labeled peptides in a proteolytic digest is described. This method relies upon the fragmentation of labeled peptides in a predictable and reproducible manner in the collision cell of a tandem mass spectrometer. The exoglycanase from Cellulomonas fimi, endoglucanase C from Clostridium thermocellum, and the β-glucosidase from Agrobacterium faecalis were labeled using 2-deoxy-2-halo-β-glycosides, digested with pepsin, and subjected to HPLC-ESIMS/MS analysis, scanning in the neutral loss mode. Under these conditions only peptides that lose the (known) mass of the label are detected. Preliminary identification of candidate peptides can be achieved from the mass measured, in combination with the known sequence of the protein. Peptide identity can be confirmed through subsequent sequencing, either via further tandem MS experiments or via the Edman degradation. In all cases the peptides identified in this manner were consistent with those identified by the standard radioactive method. This mass spectrometric method represents a rapid, nonradioisotopic solution to the problem of identifying a modified peptide in a complex mixture. The technique is also sensitive, requiring only picomole amounts of protein.

Ion trap mass spectrometry. Using high-pressure ionization.

The quadrupole ion trap, operated with a relatively high-pressure bath gas, occupies a unique place among mass analyzers. As an ion storage device, it shares many characteristics with the ICR instrument, but the use of a light bath gas and mass-selective instability for mass analysis contrasts with normal ICR operation. The bath gas facilitates the capture of ions injected into the oscillating quadrupole field and cools the ions to the center of the ion trap before mass-selective ejection. The bath gas also provides a conduit for heating ions. Mild collisional activation conditions can dissociate clusters, such as solvated analyte ions, formed by ES. Dissociation of covalently bound ions can be used to obtain structural information as part of a tandem MS experiment or to destroy polyatomic species in elemental analyses. The moderate background pressure requirements of the ion trap using mass-selective instability make it a natural mass analyzer to be coupled with high-pressure ionization methods. The ion trap can provide a significant advantage in efficiency over beam-type mass spectrometers, which translates into lower detection limits. Lower detection limits can be realized from superior duty cycle and MS/MS efficiency, although transmission for single-stage MS is comparable. The greatest advantage in efficiency can be obtained with weak ion beams that require long ion accumulation times and therefore high duty cycles. This, in part, makes the ion trap particularly attractive for ES. Bright ion sources can provide similar advantages if major ion beam components can be ejected during ion accumulation to minimize the deleterious effects caused by ion-ion interactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple “Remote Functionalization” of Different Sites in Flexible Molecules by “Anchored” Bare FeI Ions

Regiospecific, consecutive elimination of alkene and hydrogen—that turns out to be the pathway for what is formally an alkane elimination from the Fe⊕ complex of the α-branched carbonitrile 1. Both alkyl chains of 1 participate in this fragmentation, as shown by tandem MS experiments. R(CH2)5CD3, R′C3H7.

Revision and Modification of the Traditional Mechanism of CH/CC Activation by “Naked” Transition‐Metal Ions

Why Fe⊕‐complexed n‐propylamine decomposes into H2, NH3, ethylene and propylene in the mass spectrometer cannot be explained in terms of current concepts. Tandem MS experiments with deuteriated n‐propylamine enable an explanation: H2, NH3 and propylene could be formed via an n‐propyl‐Fe⊕‐NH2 complex, which rearranges to the propene complex. For the formation of ethylene, a route via a four‐membered FeNC2 complex and its conversion into an ethylene complex is possible.