Time-of-flight mass spectrometry for ions of large energy spread

Gohl, W.; Kutscher, R.; Laue, H.; Wollnik, H.

doi:10.1016/0020-7381(83)87114-9

Cited by 51 publications

(14 citation statements)

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“…By neglecting the post-accelerating term, we force the coefficients of s and s2 to vanish simultaneously." We then get d, and db both connected to D if n is given: (25) (26) or by eliminating n we obtain the relation given in Ref. (27) The connection between the two ratios is represented in Fig.…”

Section: )mentioning

confidence: 97%

Ion‐Optical solutions in time‐of‐flight mass spectrometry

Ioanoviciu¹

1995

Rapid Comm Mass Spectrometry

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Time-of-flight mass spectrometers are able to cover mass ranges to around a half a million Da. The mass resolution of these instruments has been improved drastically by incorporation of electrostatic mirrors. The ionoptical solutions enabling these achievements and other promising features are discussed in terms of: First-and second-order space focusing in time for linear drift time-of-flight mass spectrometers; velocity focusing by time lag; ion-packet bunching in post-source impulse focusing; first-and second-order energy focusing in time, in single-and double-stage homogeneous electrostatic mirrors with normal and oblique ion incidence; gridless designs; perfect time focusing in parabolic potential and axial symmetry; cylindrical ion mirrors and toroidal electrostatic deflectors as time-of-flight mass analyzers; three electrostatic sector geometry applied in secondary ion microscopy and four toroidal sector systems for tandem mass spectrometry; poloidal electrostatic sectors. Estimation of time-of-flight mass spectrometer performance limits is discussed and the stable as well as the metastable peak shapes found in time-of-flight mass spectra.Time-of-flight (TOF) mass spectrometry possesses several outstanding and unique features:' an essentially unlimited mass range, the possibility of obtaining complete mass spectra from each ion packet, and potentially high sensitivity. To take full advantage of these features, the technique requires appropriate electronics for fast ion counting and a suitable design for the TOF mass analyser.The essential performance attributes of a mass spectrometer are its resolution, sensitivity and mass range. In time-of-flight mass spectrometry two groups of different mass ions are separated if they arrive at the detector at different times. Mass resolution of all types of mass spectrometer are defined in terms of the depth of the valley separating two equal intensity adjacent and overlapping peaks. Often the full width at half maximum (FWHM) definition is used where a valley is just discernable (Fig. 1). Other definitions require adjacent peaks to be resolved by deeper, typically by a 0% or 50%, valley (Fig. 2). To have the Gaussian peaks truly separated, as in Fig. 2, Am must be about 1.4 times greater than the FWHM resolution that is shown in Fig. 1. For TOFMS the ion cloud at the detector is the result of the convolution of the initial spatial and temporal ionic distributions: transformed by the spectrometer's transfer function. A simplified representation, as constant chargedensity cylinder^,^ operates with ion packets of circular outline the aberrations at the detector site being added as slices to that cylinder. In this case, two ion packets are completely resolved if one time channel is empty between their arrival. The FWHM definition corresponds to two packets just touching each other.The front of the packet of ions of mass m reaches the detector at some time t,, while a following packet of mass m + Am arrives tm+Am -tm later. The arrival of the second ion packet must leave en...

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Section: )mentioning

confidence: 97%

Ion‐Optical solutions in time‐of‐flight mass spectrometry

Ioanoviciu¹

1995

Rapid Comm Mass Spectrometry

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“…For some arbitrary ion, formed at a distance s behind the source reference plane, we substitute h = d + s and the initial velocity component uzi= ula in Eqns (1) and (2). The flight time fs through a single-field ion source is obtained as:…”

Section: Flight Timesmentioning

confidence: 99%

Complete third‐order resolution formulae for time‐of‐flight mass spectrometers incorporating reflectrons

Ioanoviciu

1993

Rapid Comm Mass Spectrometry

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The resolution of single-and double-stage, homogeneous electric mirror time-of-flight mass spectrometers can be calculated with the derived formulae for detectors located normally to the ion flight direction or parallel to the mirror face. These formulae account for contributions to the peak width from ion initial velocity and position in the source ('turn around' time included), from ion-packet longitudinal and transverse size at the source h a l grid, as well as due to the angular ion spread. Third-order terms are included for beam size, angular aperture and velocity spread, the incidence angle being small. The field-free space needed to obtain energy focusing in time is connected with the length of the accelerating space inside the source.Since the first use of electrostatic mirrors,' their theory has been developed by Gohl et al.,' the resolution of time-of-flight mass spectrometers employing this device being increased to 35Formulae to calculate resolution for single-and double-stage homogeneous electric-field mirror reflectrons have been previously derived in Ref. 4. The second-order components of the detected ion-packet length were accounted for, oblique incidence being assumed. However, flight time inside the ion source and the initial velocity effect (leading to the so-called 'turn around' time) were disregarded. They apply for detectors located parallel to the mirror face.Perturbative effects of the slightly tilted grids or detectors have been simulated by Riggi.' The resolution limitations introduced by wire meshes were calculated in Refs 6 and 7. The results obtained are difficult to include in an analytical resolution formula.The flight time inside the accelerating gap of a singlefield ion source has been given in Ref. 8. Recently, second-order fringing field effects were calculated for single-stage electrostatic mirrors.' A fringing field with plane symmetric structure was assumed, that is unusual for reflectrons.Because in two-stage electrostatic mirror time-offlight mass spectrometers the second-order time aberration coefficient of the energy spread is cancelled, the third-order term becomes relevant. Also cross terms may contribute significantly to the detected packet length.We derive third-order resolution formulae and compare, for various source types and mass spectrometer geometries, the resolution values obtained when thirdorder terms are accounted for and also when they are neglected. FLIGHT TIMESThe flight time, t, through a homogeneous electric field may be calculated with the formulae of Ref. 10 rewritten in the form: t = (ud-uzi)ml(eE) where m , e, uzi, uZf are respectively the ion mass, its electric charge, the velocity components along the direction of the electric field (E), at the ion entry and exit, h being the distance between the field-limiting planes (Fig. 1). E is positive if ions are accelerated. When E < 0 and uzf= 0, Eqn (1) gives half of the 'turn around' time of ions in that field.We define: (1) the source reference plane, located in the ionization region normal to the ion-...

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“…The latter offers a more compact experimental set-up, with the same efficiency in energy focusing, than a homogeneous reflector [20]. For actual peak shape calculations, we chose a reference trajectory characterized by zero initial kinetic energy and coincidence with the axis of the flight tube.…”

Section: Gw (84mentioning

confidence: 99%

Peak shape determination in laser microprobe mass analysis

Vertes

Juhász

Matus

1986

International Journal of Mass Spectrometry and Ion Processes

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Potential distributionand ion trajectory calculations involving time development of the ion motion in laser microprobe mass spectrometers have been performed. Potential distribution calculations were based on the Fourier transformation technique since this offers improved effectiveness.The time-dependent ion trajectories that were calculated showed different flight times for ions with different initial conditions. Transmission properties of the angle focusing "einzel" lens are discussed with special emphasis on lens potential and ion formation position dependence.Qualitative agreement with experimental findings is demonstrated. It was shown that, if the geometrical parameters of the instrument are optimized, an arrangement promising similar performance to that of LAMMA 500 can be obtained but with more compact design.Peak shape calculations were carried out for different initial kinetic energy and departing angle distributions.Peak broadening, shift, and asymmetry could be explained in terms of the width of ion energy distribution.However, no dramatic broadening was observed according to the second-order energy focusing property of the ion reflector.

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Time-of-flight mass spectrometry for ions of large energy spread

Cited by 51 publications

References 0 publications

Ion‐Optical solutions in time‐of‐flight mass spectrometry

Ion‐Optical solutions in time‐of‐flight mass spectrometry

Complete third‐order resolution formulae for time‐of‐flight mass spectrometers incorporating reflectrons

Peak shape determination in laser microprobe mass analysis

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