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Intro to UV-Vis Molecular Absorption Spectrometry Chap 13

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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  1. Intro to UV-Vis Molecular Absorption Spectrometry Chap 13

  2. Beer's Law • A = εbc = -logT = -log(P/Po) • Absorbance is additive: • Atotal = A1 + A2 ...= ε1bc1 + ε2bc2... • Only if species do not react chemically!

  3. Limitations of Beer's Law (pp 338 - 348) • Real limitations: • Interactions at c > 0.01 M • Refractive index change at high c

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

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

  6. Effect of Polychromatic Radiation on Beer’s law (Fig 13-5)

  7. Fig. 7-2 (a) p 166

  8. Typical UV-Vis Spectrophotometers Single-beam Fig 13-13 (a)

  9. Typical UV-Vis Spectrophotometers Double-beam in Space Fig 13-13 (b)

  10. Typical UV-Vis Spectrophotometers Double-beam in Time Fig 13-13 (c)

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

  12. Fig. 10-8 Used in ICP

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