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Z-mode excitation

Possible Solutions Because z-mode excitations degrade the performance of FTMS, methods to minimize z-mode excitations are necessary. Theoretical (Equation 1) and experimental results suggest several possible strategies. [Pg.41]

The observations that there is an "optimum" orbit size and that peaks split for orbits not too much larger than the optimum orbit suggest that the optimum orbit occurs because of special circumstances. One possible circumstance is a coincidence of frequencies for ions with low and high z-mode amplitudes so that if there are mass discriminating differences in the way the ions populate the trap or in the way ions are excited, then systematic mass measurement errors can be expected. Excitation of the cyclotron mode does produce a spread in cyclotron radii, and mass discriminating z-mode excitation is discussed elsewhere in this chapter. Thus, frequency variations that cause systematic mass errors are due in part to trap field inhomogeneities. These effects are evident at low ion populations and may be due in part to excitation induced ion cloud deformation which increases with ion number. [Pg.47]

Z-Mode Excitation Excitation of ions at their trapping... [Pg.198]

Another tool is the numerical integration of the ion equations of motion. Mclver (27) and Marshall (2J3) have made use of this tool for studying some aspects of ion motion. Here, to corroborate that mass discriminating z-losses do occur, the trajectory of single ions were calculated under conditions chosen to imitate normal conditions for which symptoms of z-excitation are observed. For the calculations, the ions were started on the z-axis and were given different z-mode energies. The chirp excitation was 9.67 volts base-to-peak at each excitation plate with a 2.105 kHz/ysec sweep... [Pg.39]

We have developed a model to explain the time dependent change in sensitivity for ions during excitation and detection. The first step is to describe the image charge displacement amplitude, S(Ap, Az), as a function of cyclotron and z-mode amplitudes. The displacement amplitude was derived using an approximate description of the antenna fields in a cubic cell. The second step in developing the model is to derive a relationship to describe the cyclotron orbit as a function of time for an rf burst. An energy conservation... [Pg.42]

Because low amplitude RF burst waveforms do not significantly modify the z-mode amplitudes of ions, the intensities would be expected to reflect the z-mode amplitude distribution just before excitation. This gives us one means of checking the above hypothesis by allowing the z-mode amplitudes to relax via ion-molecule collisions, the relative peak intensities should change. Indeed, at long delay, the high frequency peak increases at the expense of the low frequency peak. [Pg.47]

For low ion populations, a first estimate of achievable ejection resolution might be obtained from the cyclotron frequency spread that occurs over the range of cyclotron orbit radii through which the ion must pass to be ejected. This is based on the notion that an ejection waveform that is just adequate to eject one ion must have a frequency spectral peak that is at least as wide as the above spread of frequencies. Such a waveform would then excite, at least to some extent, all ions with frequencies falling within the width of the peak, thus limiting the ejection resolution. For ions with low z-mode amplitudes, we can use Dunbar s (46) approximate expression for the average radial field strength,... [Pg.52]

The /w/z-selective instabihty mode for mass analysis in the ion trap allows additional experiments to be performed in the ion trap. When it is possible to selectively store ions of a particular m/z and eject other ions, the selection of a precursor ion for product-ion MS-MS is possible as well. The precursor ion is selected by applying two consecutive waveforms which eject all ions with m/z values on either side of the selected m/z. The isolated m/z is then excited by the application of a wz/z-selective excitation waveform to the end-cap electrodes. The... [Pg.37]

GC column 5% diphenyl-95 % dimethylpolysiloxane 30 m x 0.25 mm i.d. 0.25-pm. Oven temperature from 80 to 300 °C at 5°C/min ionization type El isolation window 3.0m/z MS/MS waveform resonant mode excitation amplitude 0.40 V excitation time 20mse. [Pg.307]

Here we determine the amplitudes of bound and radiation modes excited by a prescribed distribution of currents J, which occupy a volume y between the planes z = Zi and z = Z2 of a waveguide, as shown in Fig. 31-1. The total fields everywhere in the waveguide are expanded in terms of the complete set of forward- and backward-propagating modes... [Pg.608]

Michaels C A, Mullin A S, Park J, Chou J Z and Flynn G W 1998 The collisional deactivation of highly vibrationally excited pyrazine by a bath of carbon dioxide excitation of the infrared inactive (10°0), (02°0), and (02 0) bath vibrational modes J. Chem. Phys. 108 2744-55... [Pg.3015]

The DECP model successfully explained the observed initial phase of the fully symmetric phonons in a number of opaque crystals [24]. The absence of the Eg mode was attributed to an exclusive coupling between the electrons photoexcited near the r point and the fully symmetric phonons. A recent density functional theory (DFT) calculation [23] demonstrated this exclusive coupling as the potential energy surface (Fig. 2.4). The minimum of the potential surface of the excited state shifted significantly along the trigonal (z) axis,... [Pg.27]

Fig. 11.16. Representation of three tandem mass spectrometry (MS/MS) scan modes illustrated for a triple quadrupole instrument configuration. The top panel shows the attributes of the popular and prevalent product ion CID experiment. The first mass filter is held at a constant m/z value transmitting only ions of a single mlz value into the collision region. Conversion of a portion of translational energy into internal energy in the collision event results in excitation of the mass-selected ions, followed by unimolecular dissociation. The spectrum of product ions is recorded by scanning the second mass filter (commonly referred to as Q3 ). The center panel illustrates the precursor ion CID experiment. Ions of all mlz values are transmitted sequentially into the collision region as the first analyzer (Ql) is scanned. Only dissociation processes that generate product ions of a specific mlz ratio are transmitted by Q3 to the detector. The lower panel shows the constant neutral loss CID experiment. Both mass analyzers are scanned simultaneously, at the same rate, and at a constant mlz offset. The mlz offset is selected on the basis of known neutral elimination products (e.g., H20, NH3, CH3COOH, etc.) that may be particularly diagnostic of one or more compound classes that may be present in a sample mixture. The utility of the two compound class-specific scans (precursor ion and neutral loss) is illustrated in Fig. 11.17. Fig. 11.16. Representation of three tandem mass spectrometry (MS/MS) scan modes illustrated for a triple quadrupole instrument configuration. The top panel shows the attributes of the popular and prevalent product ion CID experiment. The first mass filter is held at a constant m/z value transmitting only ions of a single mlz value into the collision region. Conversion of a portion of translational energy into internal energy in the collision event results in excitation of the mass-selected ions, followed by unimolecular dissociation. The spectrum of product ions is recorded by scanning the second mass filter (commonly referred to as Q3 ). The center panel illustrates the precursor ion CID experiment. Ions of all mlz values are transmitted sequentially into the collision region as the first analyzer (Ql) is scanned. Only dissociation processes that generate product ions of a specific mlz ratio are transmitted by Q3 to the detector. The lower panel shows the constant neutral loss CID experiment. Both mass analyzers are scanned simultaneously, at the same rate, and at a constant mlz offset. The mlz offset is selected on the basis of known neutral elimination products (e.g., H20, NH3, CH3COOH, etc.) that may be particularly diagnostic of one or more compound classes that may be present in a sample mixture. The utility of the two compound class-specific scans (precursor ion and neutral loss) is illustrated in Fig. 11.17.

See other pages where Z-mode excitation is mentioned: [Pg.37]    [Pg.37]    [Pg.39]    [Pg.39]    [Pg.41]    [Pg.37]    [Pg.37]    [Pg.39]    [Pg.39]    [Pg.41]    [Pg.392]    [Pg.37]    [Pg.37]    [Pg.41]    [Pg.41]    [Pg.44]    [Pg.45]    [Pg.55]    [Pg.290]    [Pg.106]    [Pg.124]    [Pg.105]    [Pg.105]    [Pg.415]    [Pg.449]    [Pg.163]    [Pg.59]    [Pg.121]    [Pg.151]    [Pg.502]    [Pg.289]    [Pg.433]    [Pg.229]    [Pg.249]    [Pg.504]    [Pg.390]    [Pg.357]    [Pg.33]    [Pg.261]    [Pg.241]    [Pg.297]   


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