Week04.pdf - UV-Vis(Absorption Spectrometry Beer's Law A =...

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UV-Vis (Absorption) Spectrometry (Chapters 13, 14) Beer's Law: A = ε bc = - logT = - log I I 0 = log I 0 I Absorbance is additive A total = A 1 + A 2 ... = ε 1 bc 1 + ε 2 bc 2 ... in a 2 component mixture A λ 1 = ε 1, λ 1 b c 1 + ε 2, λ 1 b c 2 A λ 2 = ε 1, λ 2 b c 1 + ε 2, λ 2 b c 2 Limitations of Beer's Law (pp 303-311): (1) Chemical effects - analyte associates, dissociates or reacts to give molecule with different ε Fig 13-3 CEM 333 page 4.1
(2) Physical effects - stray light, polychromatic radiation or noise A λ 1 = - logT λ 1 = ε λ 1 bc = log I 0 I λ 1 I λ 1 = I 0 λ 1 10 λ 1 bc I λ 2 = I 0 λ 2 10 λ 2 bc A λ = I 0 λ 1 + I 0 λ 2 I λ 1 + I λ 2 = I 0 λ 1 + I 0 λ 2 I 0 λ 1 10 λ 1 bc + I 0 λ 2 10 λ 2 bc A λ = log I 0 λ 1 + I 0 λ 2 ( 29 - log I 0 λ 1 10 λ 1 bc + I 0 λ 2 10 λ 2 bc ( 29 CEM 333 page 4.2
non-linear calibration curve (Fig 13-4, 13-5) CEM 333 page 4.3
Typical UV-Vis Spectrophotometers: (Fig 13-12) includes λ selection (a) single beam (SB) (b) double-beam (DB)-in-space (c) double- beam-in-time CEM 333 page 4.4

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