MALDI ion trap

There are numerous other reports that illustrate the potential use of MALDI-TOF-MS for the rapid identification of various strains of B. anthracis. For instance, by using a new hybrid ion-trap MALDI-TOF instrument, in situ proteolytic digestion of... 

Tables 6.27 and 6.31 show the main characteristics of ToF-MS. ToF-MS shows an optimum combination of resolution and sensitivity. ToF-MS instruments provide up to 40000 spectra s-1, a mass range exceeding 100000 (in principle unlimited), a resolution of 5000, and peak widths as short as 200 ms. This is better than quadruples and most ion traps can handle. Unlike the quadrupole-type instrument, the detector is detecting every introduced ion (high duty factor). This leads to a 20- to 100-times increase in sensitivity, compared to QMS used in scan mode. The mass range increases quadratically with the time range that is recorded. Only the ion source and detector impose the limits on the mass range. Mass accuracy in ToF-MS is sufficient to gain access to the elemental composition of a molecule. A single point is sufficient for the mass calibration of the instrument. ToF mass spectra are commonly calibrated using two known species, aluminium (27 Da) and coronene (300 Da). ToF is well established in combination with quite different ion sources like in SIMS, MALDI and ESI.

Moyor, S. C. Marzilli, L. A. Woods, A. S. Laiko, V. V. Doroshenko, V. M. Cotter, R. J. Atmospheric pressure matrix-assisted laser desorption/ionization (AP MALDI) on a quadrupole ion trap mass spectrometer. Int. I. Mass Spectrom. 2003, 226,133-150. 

It should be pointed out that FAB, MALDI, and ESI can be used to provide ions for peptide mass maps or for microsequencing and that any kind of ion analyzer can support searches based only on molecular masses. Fragment or sequence ions are provided by instruments that can both select precursor ions and record their fragmentation. Such mass spectrometers include ion traps, Fourier transform ion cyclotron resonance, tandem quadrupole, tandem magnetic sector, several configurations of time-of-flight (TOF) analyzers, and hybrid systems such as quadrupole-TOF and ion trap-TOF analyzers. 

Warscheid, B. Jackson, K. Sutton, C. Fenselau, C. MALDI analysis of Bacilli in spore mixtures by applying a quadrupole ion trap time-of-fhght tandem mass spectrometer. Anal. Chem. 2003, 75, 5608-5617. 

The mass-selective instability mode of operation permits the selection and trapping of all ions created over a specified period with subsequent ejection to the detector.26 Ions with different m/z values can be confined within the ion trap and scanned singly by application of voltages that destabilize the orbits of the ions and eject them to the detector. Ion trap instruments interface readily with liquid chromatography, ESI,15 and MALDI.27 The motions of the ions and the dampening gas (e.g., helium) concentrate around the middle of the ion trap, thereby diminishing ion loss through collisions with electrodes. 

In a reflector TOF instrument, PSD can be performed. The Qq-TOF is an oa-TOF with a quadrupole as a precursor selector. TOF-TOF is a type of instrument that has emerged in recent years and has enabled MALDI-TOF instruments that can deliver good MS/MS data. There are also examples of instruments with two consecutive reflector TOFs. TOF analyzers can also be coupled to ion traps and to sector instruments. See Chapter 3 for more thorough MS/MS descriptions. 

B. Warscheid, K. Jackson, C. Sutton, and C. Fenselau. MALDI Analysis of Bacilli in Spore Mixtures by Applying a Quadrupole Ion Trap Time-of-Flight Tandem Mass Spectrometer. Anal. Chem., 75(2003) 5608-5617. 

Ion traps, ICR eells as well as QITs, are best operated with the number of trapped ions elose to their respeetive optimum, beeause otherwise ion trajectories are distorted by eoulombie repulsion. Henee, external ion sourees in eombination with ion transfer opties eapable of eontrolling the number of ions injeeted are ideally attaehed to ion traps. Currently, MALDI [207] and ESI (Fig. 4.54) [192-194,199,208] ion sourees are predominating in FT-ICR work. The ion produetion may either be regulated by the souree itself, or alternatively, by some deviee to eolleet and store the desired amount of ions from that source until injection into the ICR. For that purpose, linear RF multipole ion traps are often employed (Chap. 4.4.6), [118,209] but other systems are also in use. [195] RF-only multipoles are eommonly used to transfer the ions into the cell (Chap. 4.4.4). For the injeetion, it is important to adjust the conditions so that the ions have low kinetic energy in z-direction in order not to overcome the shallow trapping potential. 

API offers unique opportunities for the implementation of new sources or to develop new applications. Atmospheric pressure matrix assisted laser desorption (AP-MALDI) [21] can be mounted on instruments such as ion traps which were originally designed only for electrospray and LC-MS. New API desorption techniques such as desorption electrospray (DESI) [22] or direct analysis in real time (DART) [23] have been described and offer unique opportunities for the analysis of surfaces or of solid samples. 

HPLC-LTQ/FTMS N-Unked glycosylation structures in human plasma HPLC-Ion Trap MS Proteins expressing differences among isolates of Meloidogyne spp. HPLC-MALDI Monosaccharide anhydride levoglucosan, galactosan, and mannosan in the... 

Define the unit dalton. From this definition, compute the mass of 1 Da in grams. The mean of 60 measurements of the mass of individual E. coli cells vaporized by MALDI and measured with a quadrupole ion trap was 5.03 ( 0.14) X 10 °Da.3 Express this mass in femtograms. 

MALDI-IMS has been employed extensively to investigate the distribution of either commercially available or prospective drugs in tissues. Troendle et al. (1999) reported using MALDI in conjunction with a quadrupole ion trap equipped with a laser microprobe to detect the dmg paclitaxel [molecular weight (MW) 853] from rat liver and human ovarian tumor tissue. The liver tissue was incubated with a solution of paclitaxel, while the ovarian tumor tissue was from an animal dosed with paclitaxel in vivo. The concentration of drug was approximately 50mg/kg in each tissue of interest. In both cases, no localization of the dmg was observed. 

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