Combined Analytical Methods

Key Questions

  • How can spectroscopy be used as a qualitative analysis technique?

    Answer:

    See explanation below.

    Explanation:

    Spectroscopy could be used as a qualitative analysis technique by monitoring a particular characteristics of products or reactants in a chemical reaction.

    For example, infra-red ( IR ) spectroscopy, nuclear magnetic resonance ( NMR ) or ultraviolet-visible spectrophotometer ( UV-Vis ) could be used to monitor the appearance of a product or disappearance of a reactant.

    In IR and NMR, we look for the appearance of a new peaks for products or reducing the intensity or disappearance of a particular peaks for a reactant.

    Using UV-Vis spectrophotometer, we can look for new absorption wavelengths that are particular to a product, and so on.

    I hope this helps.

    Here is a video where we have used a spectrophotometer to monitor the progress of a reaction:

    Dr. Hayek · 1 · Sep 27 2015
  • How does mass spectrometry differ from other forms of spectroscopy?

    While Mass Spec isn't necessarily the greatest in nondestructive sampling (if you have a cheap instrument that's only a few ten thousand dollars), there are forms of Mass Spec ionization chambers that involve soft ionization, which is less destructive sampling, so it's not so bad now! :)

    For example, Matrix-Assisted Laser Desorption Ionization (MALDI) involves a sample matrix that basically absorbs a laser ionization source, and acts as an intermediate body between the laser and the atoms, and after the matrix gets ionized, it ionizes the atoms. That's an indirect, soft ionization, which fragments less, allowing easier observation of the parent peak(s).

    What Robb G. was referring to was Electron Impact Mass Spec, specifically (although Electron Ionization is more accurate, because there is no actual collision), and that's not favored as much anymore.

    There are much better Mass Spec ionization chamber variations, like CI and ESI, and there are other kinds of Mass Specs that ARE nondestructive, like Fourier Transform Ion Cyclotron Resonance (FTICR), Time-of-Flight (TOF) spectrometers, and Orbitraps, but they are on the more expensive end of mass analysis instrumentation out there (on the order of $800000~$2000000 for FTICR spectrometers).

    Truong-Son N. · 1 · Jun 25 2015

Questions

Infrared Spectroscopy