《仪器分析 Instrumental Analysis》课程教学资源（教材讲义）04 UV-Vis（Absorption）Spectrometry

UV-Vis(Absorption)Spectrometry (Chapters 13,14) Beer's Law: A=ebc=-logT=-log=log Io Absorbance is additive Atotal =A1+A2. =E1bC+￡2bc2. in a 2 component mixture A%1=81,1bC1+82,1bc2 A2=81,2bC1+82,.2bC2 Limitations of Beer's Law (pp 303-311): (1)Chemical effects-analyte associates,dissociates or reacts to give molecule with different s 1.000 0.800 0.600 元=430nm .40 2=570nm 0.20 .00 4.00 8.00 12.00 16.00 Indicator concentration,Mx10 Fig 13-3 CEM 333 page 4.1

UV-Vis (Absorption) Spectrometry (Chapters 13, 14) Beer's Law: A = ebc = -logT = -log I I0 = log I0 I Absorbance is additive Atotal = A1 + A2 . = e1bc1 + e2bc2 . in a 2 component mixture Al1 = e1,l1 × b× c1 + e2,l1 × b× c2 Al2 = e1,l2 ×b ×c1 + e2,l2 × b ×c2 Limitations of Beer's Law (pp 303-311): (1) Chemical effects - analyte associates, dissociates or reacts to give molecule with different e Fig 13-3 CEM 333 page 4.1

(2)Physical effects-stray light,polychromatic radiation or noise Ax=-l0gT =x bc 1o =1og1) 11=l010ac 12=l021082c 104+l02 A1x+122 L01+02 (10210+10,10ag Az=loe0x1+102）1og0,10e+10,10e） CEM 333 page 4.2

(2) Physical effects - stray light, polychromatic radiation or noise Al1 = -logTl1 = el1 bc = log I0 I æ è ç ö ø ÷ l1 I l1 = I 0 l1 10-e l1 bc I l2 = I0 l2 10 -e l2 bc Al = I 0 l1 + I 0 l2 I l1 + Il 2 æ è ç ç ö ø ÷ ÷ = I 0 l1 + I 0 l2 I0 l1 10-e l1 bc + I0 l2 10-e l2 bc æ è ç ç ç ö ø ÷ ÷ ÷ Al = log I 0 l1 + I 0 l2 ( ) - log I 0 l1 10-e l1 bc + I 0 l2 10-e l2 bc ( ) CEM 333 page 4.2

>non-linear calibration curve (Fig 13-4,13-5) 1.00 0.80 410删 兰0.60 36捌 20.40 g2380 0.20 2.04.06.08.010.0 Concentration,Mx 104 Band A Band b -Band A Band B Wavelength Concentration CEM 333 page 4.3

® non-linear calibration curve (Fig 13-4, 13-5) CEM 333 page 4.3

Typical UV-Vis Spectrophotometers: (Fig13-12) includesλselection Filter or Amplifier Filter or monochromator Amplifier Filter or (a)single beam (SB)(b)double-beam (DB)-in-space (c)double- beam-in-time CEM 333 page 4.4

Typical UV-Vis Spectrophotometers: (Fig 13-12) includes l selection (a) single beam (SB) (b) double-beam (DB)-in-space (c) double￾beam-in-time CEM 333 page 4.4

Multichannel Spectrophotometer No monochromator,but disperses transmitted light and measures"all wavelengths at once"(Fig 13-13) Polychromatic sour 米 Lens Photodiode array No scanning-simple and fast More expensive Limited resolution CEM 333 page 4.5

Multichannel Spectrophotometer No monochromator, but disperses transmitted light and measures "all wavelengths at once" (Fig 13-13) No scanning - simple and fast More expensive Limited resolution CEM 333 page 4.5

Applications of UV-Vis Spectrometry: M+h excitation M relaxationM+h/heat How probable? ranges 0 to ~100,000 L/mol.cm "forbidden" "allowed" electronic transition Which electrons get excited? In UV-Vis.photon provides enough energy to move outer valence (bonding)electrons Organic molecules Ψo=ΨsA+ΨsB Bonding o molecular orbital Ψ。*=ΨsA-ΨsB Antibonding o molecular orbital Ψx=Ψpa+WPB Bondingπmolecular orbital x*=ΨpA-ΨpB Antibonding n molecular orbital (c)o*orbital (b)πorbital (dπ*orbital Fig 14-1 CEM 333 page 4.6

Applications of UV-Vis Spectrometry: M + hu excitation ¾ ¾ ¾ ¾ ¾ ® M * relaxation ¾ ¾ ¾ ¾ ¾ ® M + hu / heat How probable? e ranges 0 to ~100,000 L/mol·cm "forbidden" "allowed" electronic transition Which electrons get excited? In UV-Vis, photon provides enough energy to move outer valence (bonding) electrons Organic molecules ys = ysA + ysB Bonding s molecular orbital ys * = ysA - ysB Antibonding s * molecular orbital yp = ypA + ypB Bonding p molecular orbital yp * = ypA - ypB Antibonding p * molecular orbital Fig 14-1 CEM 333 page 4.6

o,n(bonding)and n (non-bonding)electrons e:0 XER 0=m Fig 14-2 Arrange in terms of energy: .Antibonding Antibonding 6 6 Nonbonding Bonding Bonding Fig 14-3 0→0* AE large (<150 nm)8=10-10,000 L/mol.cm n-→g* (halogens,N,O,S)AE smaller (A=150-250 nm) 8=200-2000 L/mol-cm π→π*n→π*△E small(=200-700nm)e=10-10,000L/mol.cm Ideal for UV-Vis spectrometry of organic chromophore CEM 333 page 4.7

s, p (bonding) and n (non-bonding) electrons Fig 14-2 Arrange in terms of energy: Fig 14-3 s®s* DE large (l<150 nm) e=10-10,000 L/mol·cm n®s* (halogens, N, O, S) DE smaller (l=150-250 nm) e=200-2000 L/mol·cm p®p* n®p* DE small (l=200-700 nm) e=10-10,000 L/mol·cm Ideal for UV-Vis spectrometry of organic chromophore CEM 333 page 4.7

Red shift of Amax with increasing conjugation CH2=CHCH2CH2CH=CH2 Amax =185 nm CH2=CHCH=CH2 Amax=217 nm Red shift of Amax with of rings Benzene入max=204nm Naphthalene Amax=286 nm Blurred with solvent (a)Vapor W 450 500 550 600 Wavelength,nm Fig 14-5 CEM 333 page 4.8

• Red shift of lmax with increasing conjugation CH2=CHCH2CH2CH=CH2 lmax =185 nm CH2=CHCH=CH2 lmax =217 nm • Red shift of lmax with # of rings Benzene lmax =204 nm Naphthalene lmax =286 nm • Blurred with solvent Fig 14-5 CEM 333 page 4.8

Inorganic Ions Most transition metal ions are colored (absorb in UV-vis)due to d->d electronic transitions(Fig 14-7) 400 500 600 700 80 0.900 400 500 600 C02 A00 600 300 400 00 0.1 1 Mn2 2 400 50 lengt Remember: Solution absorbs red appears blue-green Solution absorbs blue-green appears red CEM 333 page 4.9

Inorganic Ions Most transition metal ions are colored (absorb in UV-vis) due to d®d electronic transitions (Fig 14-7) Remember: • Solution absorbs red appears blue-green • Solution absorbs blue-green appears red CEM 333 page 4.9

Ligands cause different interactions with d electrons (Fig 14-8,14-9) -ligand field splitting d2.d2 d2-w2 d2 1d3d2-y2 do dwe dy d2,d.2-y2 Octahedral Tetrahedral Square planar field CEM 333 page 4.10

Ligands cause different interactions with d electrons (Fig 14-8, 14-9) - ligand field splitting CEM 333 page 4.10