Pulsed-ion extraction

Brown, R. S. Lennon, J. J. Mass resolution improvement by incorporation of pulsed ion extraction in a matrix-assisted laser desorption/ionization linear time-of-flight mass spectrometer. Anal. Chem. 1995,67,1998-2003. 

R. S. Brown and J. J. Lennon. Mass Resolution Improvement by Incorporation of Pulsed Ion Extraction in a Matrix-Assisted Laser Desorption/Ionization Linear Time-of-Flight Mass Spectrometer. Anal. Chem., 67(1995) 1998-2003. 

Note Unfortunately, establishing patents and trademarks has caused redundant names for almost the same thing Time Lag Focusing (TLF, Micromass) Delayed Extraction (DE, Applied Biosystems) Pulsed Ion Extraction (PIE, Bru-ker Daltonik). 

Fig. 4.10. Variation of potentials in pulsed ion extraction with time. The lens stack acts as angular focusing device for the ion beam. By courtesy of Bruker Daltonik, Bremen.

The final system described here is that of Jones et al. (1993), which was developed for positron-hydrogen ionization studies and is illustrated in Figure 5.10. Similar apparatus has been used by Ashley, Moxom and Laricchia (1996) (see subsection 5.4.5 below), Kara et al. (1997a, b) and Kara (1999). Several of the basic features, including the pulsed ion extraction and ion transport systems, are similar to those developed by Knudsen et al. (1990). E x B plates were introduced by Jones et al. (1993) to remove the slow positrons from the fast / + particles, secondary electrons and gamma-ray flux emanating from the source. 

To reduce the kinetic energy spread among ions with the same m/z ratio leaving the source, a time lag or delay between ion formation and extraction can be introduced. The ions are first allowed to expand into a field-free region in the source and after a certain delay (hundreds of nanoseconds to several microseconds) a voltage pulse is applied to extract the ions outside the source. This mode of operation is referred to as delayed pulsed extraction to differentiate it from continuous extraction used in conventional instruments. Delayed pulsed extraction, also known as pulsed ion extraction, pulsed extraction or dynamic extraction, is a revival of time-lag focusing, which was initially developed by Wiley and McLaren in the 1950s, shortly after the appearance of the first commercial TOF instrument. 

Instrument parameter settings For the reflector positive ion mode, ions are accelerated at 25 kV with 50 ns of pulsed ion extraction delay with the extraction voltage at 21.75 kV. The lens voltage is 9.5 kV and the reflector voltages 1 and 2 are 26.3 and 14.1 kV, respectively. The reflector detector voltage is 1.625 kV, and the laser is operated at 50 Hz repetition rate. The matrix deflection mass is 500 kDa and the mass range for acquisition is m/z 580 to 4000. We used the default LIFT method (13) for the tandem MS (TOF/TOF mode) analysis. 

Others groups [71, 72, 73, 74] obtained an improvement of mass accuracy and peak resolution by the use of a delayed extraction system [75]. This system uses a pulsed ion extraction MALDI ionisation technique increasing the accelerating voltage from 0 up to 3 kV in 300 nanoseconds. This technique allowed an increase of peak resolution for cytochrome c (12 kDa) from 350 FWHM obtained in linear mode to 1024 with a continuous ion extraction. 

Sequencing of modified oligonucleotides using in-source fragmentation and delayed pulsed ion extraction matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Int. J. Mass Spectrom., 169, 331-350. 

Combining Delayed and Pulsed Ion Extraction with Desorption Techniques... 

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