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Time-of-flight mass spectrometry (TOF for short)

Time of Flight Analyzers. Time-of-flight mass spectrometry (TOF for short) While originally used as mass analyzers for use with peptides, they are now applied to problems which range nanospray analysis of biological samples to liquid chromatography (LC/MS/MS) of pharmaceutical preparations.

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Time-of-flight mass spectrometry (TOF for short)

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  1. Time of Flight Analyzers Time-of-flight mass spectrometry (TOF for short) While originally used as mass analyzers for use with peptides, they are now applied to problems which range nanospray analysis of biological samples to liquid chromatography (LC/MS/MS) of pharmaceutical preparations. The rapid acceptance of TOF analyzers is due to their attractive combination of high sensitivity and high mass accuracy, not to mention their simplicity.

  2. TIME OF FLIGHT : Equations of motion In a linear TOF, neutral and charged fragments generated through fragmentation of ions in the drift region cannot be distinguished from the original ion, because their velocity remains the same.

  3. Mass Calibration • Resolution • Distribution in flight time • Length of ion formation pulse • Variation in initial kinetic energy • Space distribution (site of the volume)

  4. Mass Analyzers:Delayed pulsed extraction to increase resolution

  5. Mass Analyzers: TOF with REFLECTRON E: electric field in reflectron VR: potential of reflectron D: length of reflectron

  6. An ion of charge of q with a kinetic energy Ek will enter with a velocity vix and penetrate the reflectron to a depth d Mean velocity in reflectron vix/2. The time needs to penetrate d will be Then, the total time in the reflectron is

  7. The total time out of reflectron t: Total flight time TTOT: Two ions sharing the same mass m but with different kinetic energy, we define

  8. The velocity along x axis during field –free flight: The time of field-free flight: In the reflectron, the ions will penetrate at a depth d or d’: The time spent in the reflectron: Total flight time:

  9. Tandem MS with TOF Flight times of precursor and fragment in the field-free region: Same Flight times of precursor and fragment in reflectron: See textbook for details

  10. Mass Analyzers: TIME OF FLIGHT Benefits • Fastest MS analyzer • Well suited for pulsed ionization methods (method of choice for majority of MALDI mass spectrometer systems) • High ion transmission • MS/MS information from post-source decay • Highest practical mass range of all MS analyzers Limitations • Requires pulsed ionization method or ion beam switching (duty cycle is a factor) • Fast digitizers used in TOF can have limited dynamic range • Limited precursor-ion selectivity for most MS/MS experiments Applications • Almost all MALDI systems • Very fast GC/MS systems

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