RF-only

Since ions analysed with a quadnipole instniment have low translational kinetic energies, it is possible for them to undergo bimoleciilar reactions with species inside an RF-only quadnipole. These bimoleciilar reactions are often iisefiil for the stnictural characterization of isomeric species. An example of this is the work of Flanison and co-workers [17]. They probed the reactions of CH. NHVions with isomeric butenes and... 

Note that in mass spectrometry/mass spectrometry (MS/MS) applications, quadrupole and magnetic sectors can be used together advantageously. It is also worth noting that the quadrapole can be operated without the DC voltages. In this RF-only mode, no mass separation occurs, and these quadrapoles are used as ion transmission guides, described in Chapter 49. 

In its RF-only configuration (wide band-pass mode), all ions produced in an ion source and accelerated gently into the quadrupole analyzer will pass through it, whatever their m/z values. In contrast, the RF/DC mode is selective for chosen m/z values. 

The simplest example of this type of instmment is the triple quadmpole ms (27), in which and 2 used for mass analysis of the precursor and product ions, respectively, and 2 is a rf-only quadmpole coUision cell. The maximum possible energy uptake during coUisional activation, ... 

The triple quadrupole instrument consists of two mass analyzers separated by an rf-only quadrupole. In the rf-only mode, ions of all masses are... 

The quadrupole mass filter is the most abundant mass analyser today and RF-only multipoles are used as transmission devices/collision regions in various instrumental configurations. The mass filter is used extensively as a stand-alone mass analyser and as an analyser in multistage mass spectrometers. 

One of the most common couplings of analyzers for tandem MS is the triple quadrupole. Its notation is QqQ, where the capital Q indicates a quadrupole analyzer and the lowercase q is for a RF-only quadrupole that constitutes the collision cell. 

Note At first sight, there is no difference whether Qi or Q3 is switched to RF-only for MS mode. However, for El it seems better to operate Q3 in RF-only mode. Otherwise, the ion source would effectively extend up to the entrance of Q3 making fragment ions more abundant due to elongated time for dissociations. Soft ionization methods do not show such differences. 

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. 

Geometries composing of an oaTOF as MS2 bear the advantage that advanced TOFs offer accurate mass measurements close the the accuracy of magnetic sector instruments. Currently, QqTOF systems can be regarded as the commercially most successful hybrid. While the linear quadrupole serves as MSI in MS/MS experiments, it is operated in RF-only mode when tandem MS is not intended, because... 

Lock, C.M. Dyer, E. Simulation of Ion Trajectories Through a High Pressure RF-only Quadrupole Collision Cell by SIMION 6.0. Rapid Commun. Mass Spectrom. 1999., 75,422-431. 

Yost, R.A. Enke, C.G. McGilvery, D.C. Smidi, D. Morrison, J.D. High Ef-lici cy Collision-Induced Dissociation in an Rf-Only Quadrupole. Int. J. Mass Spectrom. Ion Phys. 1979, 50, 127-136. 

Enhanced Q3 single MS (EMS) RF only No fragment Trap/scan... 

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