Pulsed-source mass spectrometry

Reactions of Thermal Energy Ions by Pulsed Source Mass Spectrometry... 

Pulsed source mass spectrometry 150 Pulsing technique.132, 139... 

Ions for TOF mass spectrometry must be extracted from the ion source in instantaneous pulses. Therefore, either ions are produced continuously but are extracted from the source in pulses, or ions are produced directly in pulses. 

CA 73,100610 (1970) A pulsed ruby laser-mass spectrometry technique was developed and applied, wherein granular mixts of AP and lightabsorbing substrate materials were rapidly flash py roly zed (0.8 msec) within the low-pressure lon-source chamber of a Bendix TOF mass... 

ToF analysers are able to provide simultaneous detection of all masses of the same polarity. In principle, the mass range is not limited. Time-of-flight mass analysis is more than an alternative method of mass dispersion it has several special qualities which makes it particularly well suited for applications in a number of important areas of mass spectrometry. These qualities are fast response time, compatibility with pulsed ionisation events (producing a complete spectrum for each event) ability to produce a snapshot of the contents of the source volume on the millisecond time-scale ability to produce thousands of spectra per second and the high fraction of the mass analysis cycle during which sample ions can be generated or collected. 

In ToF-MS, the ion source is pulsed to create packets of ions. In the conventional procedure, the system waits for all the ions in a packet to reach the detector before injecting the next packet of ions. Complications arise when ToF-MS is coupled to a continuous ion source. Such coupling is therefore often accomplished by the orthogonal extraction approach, in which a segment of the ion stream is accelerated orthogonally by a push-out pulse. However, in this process, up to 95 % of the information contained in the ion steam is lost. Recently, Hadamard transform time-of-flight mass spectrometry (HT-ToFMS) was developed to couple continuous ion... 

By employing a laser for the photoionization (not to be confused with laser desorption/ ionization, where a laser is irradiating a surface, see Section 2.1.21) both sensitivity and selectivity are considerably enhanced. In 1970 the first mass spectrometric analysis of laser photoionized molecular species, namely H2, was performed [54]. Two years later selective two-step photoionization was used to ionize mbidium [55]. Multiphoton ionization mass spectrometry (MPI-MS) was demonstrated in the late 1970s [56—58]. The combination of tunable lasers and MS into a multidimensional analysis tool proved to be a very useful way to investigate excitation and dissociation processes, as well as to obtain mass spectrometric data [59-62]. Because of the pulsed nature of most MPI sources TOF analyzers are preferred, but in combination with continuous wave lasers quadrupole analyzers have been utilized [63]. MPI is performed on species already in the gas phase. The analyte delivery system depends on the application and can be, for example, a GC interface, thermal evaporation from a surface, secondary neutrals from a particle impact event (see Section 2.1.18), or molecular beams that are introduced through a spray interface. There is a multitude of different source geometries. 

In principle, it would be possible to perform multistage mass spectrometry like in an ICR analyzer although with no gas CID would of course not be possible, but other dissociation methods could be employed. There might, however, be technical issues. At the time of writing, fragmentation is performed in the linear QIT preceeding the orbitrap in Thermo Fischer Scientific s instrument. Both pulsed and continuous ion sources can be employed. There are several ion sources that can be employed with Thermo Fischer Scientific s orbitrap. 

The development of laser ionization mass spectrometry was started by Honig and Woolston in 196359 with studies of laser beam sohd surface interaction and ion formation processes. Due to the pulse character of laser-induced ions, ToF analyzers were coupled to laser ion sources in the seventies and produced commercially as LAMMA-500 and later LAMMA-1000 and 2000 (Leybold-Heraeus, Cologne, Germany). 

Another limit source of uncertainty in isotope ratio measurements by mass spectrometry is the dead time of the ion detector for counting rates higher than 106cps, because a lower number of counts are usually registered than actually occur. Dead time correction of the detector is required if extreme isotope ratios are measured by channel electron multipliers and pulsed counting systems.86... 

Selected topics in Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry instrumentation are discussed in depth, and numerous analytical application examples are given. In particular, optimization ofthe single-cell FTMS design and some of its analytical applications, like pulsed-valve Cl and CID, static SIMS, and ion clustering reactions are described. Magnet requirements and the software used in advanced FTICR mass spectrometers are considered. Implementation and advantages of an external differentially-pumped ion source for LD, GC/MS, liquid SIMS, FAB and LC/MS are discussed in detail, and an attempt is made to anticipate future developments in FTMS instrumentation. 

A plasma source was coupled to a TOF-MS as early as the 1960s, when workers at Bendix [12] used such an arrangement to analyze the chemical species in a plasma jet. The instrument utilized a pulsed supersonic inlet probe similar to that found in current inductively coupled plasma mass spectrometry (ICP-MS) quadru-pole instruments and employed a TOF-MS that was oriented at a 90° angle to the input ion beam. More importantly, however, it used a pulsed extraction field to extract ions from the plasma source and accelerate them into the flight tube. It is this concept of injecting discrete ion bunches into the TOF-MS analyzer that has been almost ubiquitously employed by workers using continuous ion sources [17,18]. 

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