Intro to UV-Vis Molecular
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Intro to UV-Vis Molecular Absorption Spectrometry Chap 13 PowerPoint PPT Presentation


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Intro to UV-Vis Molecular Absorption Spectrometry Chap 13. Beer's Law A = ε bc = -logT = -log(P/P o ) Absorbance is additive: A total = A 1 + A 2 ...= ε 1 bc 1 + ε 2 bc 2 ... Only if species do not react chemically!. Limitations of Beer's Law (pp 338 - 348). Real limitations:

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Intro to UV-Vis Molecular Absorption Spectrometry Chap 13

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Intro to UV-Vis Molecular

Absorption Spectrometry

Chap 13


  • Beer's Law

    • A = εbc = -logT = -log(P/Po)

  • Absorbance is additive:

    • Atotal = A1 + A2 ...= ε1bc1 + ε2bc2...

  • Only if species do not react chemically!


  • Limitations of Beer's Law

    (pp 338 - 348)

    • Real limitations:

      • Interactions at c > 0.01 M

      • Refractive index change at high c


    (2) Chemical effects - analyte associates, dissociates or reacts to give molecule with different ε


    (3) Instrumental effects - stray light, polychromatic radiation or noise  non-linear calibration curve (Fig 13-4)


    Effect of Polychromatic Radiation on Beer’s law

    (Fig 13-5)


    Fig. 7-2 (a) p 166


    Typical UV-Vis Spectrophotometers

    Single-beam

    Fig 13-13 (a)


    Typical UV-Vis Spectrophotometers

    Double-beam in Space

    Fig 13-13 (b)


    Typical UV-Vis Spectrophotometers

    Double-beam in Time

    Fig 13-13 (c)


    Multichannel Spectrophotometer:

    No monochromator, but disperses transmitted light and measures "all wavelengths at once" (Fig 13-14)


    Fig. 10-8

    Used in ICP


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