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Fourier Transformation of Data

  • Page ID
    291565
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    Exercise 1 – Sampling Rate (SR), Acquisition Time (AQ), and Number of Data Points (NDP)

    A type of instrument called a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR-MS) costs about the same as a nice NMR ($500k) and is used in a variety of applications where ultra-high resolution mass information is required.  The FT-ICR-MS at the Woods Hole Oceanographic Institution (pictured below) uses a sampling rate of 500 kHz and FT to produce a mass spectrum from a digitized complex waveform containing 65,536 data points in the time domain. The complex waveform contains information about ion cycling frequencies, which are in turn connected directly to ion m/z ratios.  

    FT-ICR_MassSpectrometer.jpg
    Picture from: https://www2.whoi.edu/site/ftmsfacility/intrumentation/

     

    1. When we say the FT-ICR-MS has a sampling rate of 500 kHz, describe what is being sampled?

     

     

     

     

     

    1. What is the νmax that corresponds to the sampling rate for this instrument?

     

     

     

     

     

    1. Calculate the acquisition time for a raw FT-ICR-MS data file.

     

     

     

     

     

    1. Calculate the digital resolution (Δν) for the FT-ICR-MS.

     

     

     

     

     

    1. How would you change the settings to increase the digital resolution of the FT-ICR-MS? You may reasonably assume that the size of data files is determined by the hardware/software and thus can’t be changed.

     

     

     

     

     

     

    1. Is there any danger to the change you proposed above?

     

     

     

     

    Exercise 2 – Frequency Ranges and Noise

    1. Does sampling rate influence the range of frequencies that you can detect using FT-NMR? Explain briefly.

     

     

     

     

     

     

    1. What would be the problem if a background signal due to noise (that was necessarily a component of the raw FID) had a characteristic frequency that exceeded νmax?

     

     

     

     

     

     

     

     

     

     

     

     

    1. How would you solve this problem if you were the person responsible for instrument design?

     

     

     

     

     

     

     

     

     

     

    Contributors and Attributions


    This page titled Fourier Transformation of Data is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Contributor.

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