Skip to main content
Chemistry LibreTexts

Comparing Spectroscopic Techniques

  1. Last updated
  2. Save as PDF
  • Page ID
    295969

    • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    1. Explain molecular origins and fundamental equations of spectroscopy. And illustrate energy diagrams for spectroscopic techniques (UV-Vis, FL, AA).
      1. The image below illustrates the Electromagnetic Spectrum.

        ElectromagneticSpectrum.png

        What is the relationship between the energy, frequency, & wavelength of electromagnetic radiation? 

         

         

         

         

         

      2. Draw energy diagrams (Jablonski diagrams) for the techniques listed. Indicated ABSORPTION, FLUORESCENCE, or PHOPHORESCENCE energy transitions as needed.  Use appropriate arrow notation (straight line = radiative process, wavy line = non-radiative process).

        Diagrams.png

         

         

         

      3. On one chart, crudely sketch both an excitation (EX) spectrum and an emission (EM) spectrum for the same fluorescing molecule.

        Chart.png

         

         

         

         

         

         

         

         

         

         

         

         

         

         

         

      4. What factors influence the absorbance that you would measure for a sample? Is each factor directly or inversely proportional to the absorbance? Hint: Beer’s Law

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    1. Sketch instrumental schematics for each spectrophotometer (UV-Vis, FL, AA).
      1. On your white board, draw a simple block diagram for each type of spectrometer (UV-Vis, FL, AA) outlined below. Each block diagram should include sources, wavelength selectors, detectors, sample and path of radiation. Use the tool box for help.

    ToolBox.png

    1. Instrument disassembly/analysis of a UV-Vis. The parts listed below will be addressed.
      • slit width
      • filters
      • Concave mirrors
      • monochromator
      • Beam splitter
      • two detectors
      • Sample holder
      • Double beam Spec difference
      • UV-Vis vs. Fluorometer
      • Length of spec
      • Black interior
    1. Analysis of unknown samples A, B, & C using UV-Vis, FL, AA.
      1. Scan all three samples in each of the instruments and note if spectra appears, to what extent, and at what wavelength.

        Sample

        A

        B

        C

        UV-Vis

        Peak Present:

        λ max =     

        Peak Shape:

         

        Peak Present:

        λ max =     

        Peak Shape:

         

        Peak Present:

        λ max =     

        Peak Shape:

         

        FL

        λ Ex =    

        λ Em =      

        Peak Intensity

         

        λ Ex =    

        λ Em =      

        Peak Intensity

        λ Ex =    

        λ Em =      

        Peak Intensity

         

        AA

        λ Abs =

        Absorption: Yes |No

        λ Abs =

        Absorption: Yes |No

        λ Abs =

        Absorption: Yes |No

         

      2. Three possible identities for the unknown compounds are listed below. Identify which one of them would be compound A, B, and C.
        Caffeine
        Caffeine.png
        Pyrene
        Pyrene.png
        Copper nitrate
        CopperNitrate.png

     

    1. Interrogate compound classification using three spectroscopic techniques (UV-Vis, FL, AA) and select appropriate technique.
      1. Which technique would be optimal for analysis of the following compounds? Justify your answers.
        Mn(acac)3
        Mn(acac)3.png
        Pyridine
        Pyridine.png
        Cobalt ion
        CobaltIon.png
        Anthracene
        Anthracene.png
        Cobalt hexahydrate
        CobaltHexahydrate.png
        Butane
        Butane.png

         

      2. Which sample types can be analyzed using each technique? (UV-Vis, FL, AA)



         

    Contributors and Attributions

    This page titled Comparing Spectroscopic Techniques is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Contributor via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.