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Microwave Induced Plasma (MIP)

  • Page ID
    75411
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    A microwave induced plasma is another atomic emission source. Typically, a 2.45 GHz microwave generator (magnetron) produces a wave that travels through a cable and is focused via a tuning system where a torch sits in the center of a cavity. This torch has a carrier gas flowing through the outer portion of the torch (sometimes tangentially, other times not) and the plasma is started (or ignited) via a Tesla coil or a piece of copper wire. The carrier gas continues to flow through the torch and the plasma is self-sustaining. Remember the plasma has a high electron density. Analyte is introduced into the center or inner portion of the plasma typically via a nebulizer or ETV system.

    There are several different MIPs torches developed, which include the Beennakker cavity, and microwave plasma torch, and the capacitively coupled microwave plasma.

    Carrier Gas

    Air, nitrogen, helium and argon can be used as a carrier gas. Helium and argon are easily ionized in the MIP:

    \[\ce{He + e^- \rightarrow He^+}\]

    with \(\mathrm{E_1 = 24.6 \,eV}\)

    and

    \[\ce{Ar + e^- \rightarrow Ar^+}\]

    with \(\mathrm{E_1 = 15.8\, eV}\)

    In particular, helium discharges can excite non-metals and produce emission lines the visible (and UV) spectral region:

    Cl match is great (479 nm) and S, F, Br, C, and O are good in NIR

    Exercise

    Why is this the emission source of choice for GC interfacing? Click here for the answer!

    Overall, MIP is not used readily since the limits of detection are generally worse than ICP systems. This is due to the fact that ICP has a much higher energy density, which leads to a higher vaporization of the analyte. Most of the portable atomic emission systems manufactured utilize MIPs since the generator is small and relatively low power is helpful. MIP references are here.


    This page titled Microwave Induced Plasma (MIP) is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Alexander Scheeline & Thomas M. Spudich via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.