Chapter 24 Molecular Absorption Spectrometry Molecular Spectrometry Uv / Vis / Ir Widely Used Identification Inorganic Organic Biochemical Species

Chapter 24 Molecular
Absorption Spectrometry
＊ molecular spectrometry
→ UV / Vis / IR
→ widely used
→ identification
→ inorganic ; organic
biochemical species
＊ UV / Vis → molecular
→ absorption spectrometry
→ most widely use
→ primarily
→ quantitative analysis
＊ IR → absorption spec.
→ powerful tool
→ determining structure
→ org. ; inorg. compound
→ important role
→ quantitative analysis
→ environmental pollution
24A UV/Vis Molecular Absorption Spect.
＊ type of molecule absorb UV/Vis radiation
＊ qualitative ; quantitative
→ UV / Vis spectrometry application :
․ 24A-4 → spectrophotometric titration
․ 24A-5 → composition of complex ion

Q : 問答題 (沒有圖)
請問化合物具備哪些結構上的特性，會
產生較強的 UV/visible 吸收光譜現象？
(1) organic compound double ; triple ;
π-bond ; chromophore
(2) inorganic compound transition metal
La ; Ac (4f; 5f transition)
(3) charge-transfer complex e- donor and
e- acceptor group
24A-1 Absorbing Species
(1) Absorption by Org. Compd.
＊ single-bond ; σ-bond
→ excitation → < 180 nm
→ experimental difficulty
→ quartz ; atmosphere
→ absorption → require LiF
→ optics → evacuated spec.
＊ double ; triple ; π-bond
→ not strongly held
→ easy excited by
→ UV / Vis / IR region
＊ chromophore → unsaturated
→ functional group → absorb
→ UV / Vis. radiation
＊ table 24-1 → chromophore
→ absorption λ
＊ table 24-1 → λmax. ; εmax.
→ influenced by solvent effect
→ molecular structure
→ two or more chromophore
→ conjugate → λmax. shift
→ vibrational effect
→ broad → absorption peak
→ determination
→ λmax. ; εmax. → difficulty
Q : 圖表問答題
參考 Table 24-1，請說明表中每
一欄 (如 chromophore, solvent ,
λmax , εmax ) 所代表的意義。

＊ figure 24-1 → typical spectra
→ organic compound
＊ saturated org. compound
→ contain → heteroatom
→ O ; N ; X ; S
→ nonbonding electron excited
→ UV region → 170 ~ 250 nm
＊ table 24-2 alcohol ; ether solvent
→ prevent → 180 ~ 200 nm
(2) Absorption by Inorganic Species
＊ figure 24-2 → transition metal
→ color → d-orbital transition
→ absorption visible
→ radiation → absorb energy
→ depend on → ligand bonded
→ or its oxidation state
＊ figure 24-3 → La ; Ac
→ 4f ; 5f transition
→ electron → responsible
→ absorption → shield
→ larger principle quantum # e-
→ absorption energy
→ unaffected → species
→ bonded by → outer electron
(3) charge-transfer absorption
＊ charge-transfer absorption
→ large ε → > 10 4
→ high sensitivity
→ quantitative purpose
→ org. or inorg. complex
＊ charge-transfer complex
→ e- donor group → bonded
→ e acceptor → e transition
- -
→ internal ox / red process

→ figure 24-4
＊ charge-transfer complex
→ metal → e acceptor
-
→ ligand → e- donor
24A-2 Qualitative Application
UV / Vis Spectrometry
＊ table 24-3 → 圖表問答題
→ solvent → absorb UV
→ lower → λ limit
Q : 圖表問答題
參考 Table 24-3，請說明由
表中可以得到哪些資訊？
Q : 圖表問答題
參考圖 Figure 24-5，請問如何
做實驗以獲得圖中的4條曲線？
由這 4 條曲線圖，可以得到什
麼結論？為什麼？
＊ figure 24-5 → effect of slit width
→ peak height → sensitivity
→ peak separation → resolution
․ wider bandwidth → peak distort
→ poor resolution → (1) 20 nm
․ min. slit width → resolution ↑
→ (4) → 1 nm
24A-3 Quantitative Application
＊ spectrophotometric method
→ important characteristics
1. wide application
2. high sensitivity
(略)
3. high selectivity
4. good accuracy
5. ease and convenience
24A-4 Photometric and
Spectrophotometric
Titration
＊ figure 24-13
→ analyte (A)
→ product (P)
→ titrant (T)
Q : 圖表問答題
參考圖 Figure 24-13，隨著橫
坐標(volume of titrant)增加，
請說明縱座標 (absorbance)
如何改變？為什麼？
titrant
(滴定)
P0 P
analyte
(A) (T) (P)

(滴定) analyte + titrant → product
(光譜) Atotal = Aanalyte + Atitrant + Aproduct
= εA b cA + εT b cT + εP b cP
(a) εA= εP = 0 ; εT≠ 0
titrant ․ 當量點之前：
analyte + titrant → product
(cA↓) (cT = 0) (cP↑)
Atotal = Aanalyte + Atitrant + Aproduct
A = 0 + 0 + 0
(εA= 0) (cT= 0) (εP= 0)
․ 當量點以後：
(cA= 0) (cT ↑) (cP≠ 0相同)
analyte
A↑ = 0 + A↑ + 0
(cA= 0) (εT≠0 ; cT↑) (εP= 0)
(e) εT > εP > 0 ; εA= 0
titrant ․ 當量點之前：
(cA↓) (cT = 0) (cP↑)
A↑ = 0 + 0 + A↑
(εA= 0) (cT= 0) (εP>0 ; cP↑)
․ 當量點以後：
(cA= 0) (cT ↑) (cP≠0相同)
analyte
A↑ = 0 + A↑ + A相同
(cA= 0) (εT>0 ; cT↑) (εP>0;cP相同)
Q : 圖表問答題
參考圖Figure 24-14，隨著橫座
標 (volume of titrant, EDTA) 增
加，請問縱座標 (absorbance)
如何改變？為什麼？
＊ figure 24-14 → EDTA titration
→ mixture solution → Bi3+; Cu2+
→ 2.0 x 10-3 M → Bi3+ / EDTA
→ complex first → not absorb
→ Cu2+ / EDTA→ abs. radiation

EDTA
P0 Bi3+ P
Cu2+
․ EDTA react with Bi3+ first

( ε = 0)
Bi3+ + EDTA → Bi3+/EDTA (not absorb)
․ all Bi3+ reacted, EDTA + Cu2+ ( ε ≠ 0)
Cu2+ + EDTA → Cu2+/EDTA (absorb UV)
․第一個當量點：
EDTA Bi3+ + EDTA → Bi3+/EDTA

在當量點時 Bi3+ : EDTA = 1 : 1
由EDTA的滴定量，可知 Bi3+量
Bi3+ ․第二個當量點：
Cu2+ Cu2+ + EDTA → Cu2+/EDTA

在當量點時Cu2+ : EDTA = 1 : 1
由EDTA的滴定量，可知Cu2+量
․第一個當量點之前：
Bi3+ + EDTA → Bi3+/EDTA (c ≠ 0)
EDTA (not absorb; ε = 0)
(A = ε b c = 0)
․第二個當量點之前：
Cu2+ + EDTA → Cu2+/EDTA (c↑)
Bi3+ (absorb UV ε ≠ 0)
(A = ε b c ; ε ≠ 0 ; c↑ ; A↑)
Cu2+
․第二個當量點以後：
產物(Cu2+/EDTA)的濃度不再增加
A = ε b c ; c 不再增加 ; A 不再增加
24A-5 Spectrophotometric
Study of Complex Ion
＊ complex-ion study :
x M + y L ⇋ MxLy
x = ? y = ?
(1) continuous variation
(2) mole-ratio method
(3) slope-ratio method (略)
Q : 問答題
請問 method of continuous
variation 如何製備樣品？
如何測得實驗數據？如何
作圖？如何由圖得到結論？
(1) method of continuous variation
(略)
․ prepare → series of solution
→ M : L → (9:1) (8:2) (7:3)
․ measure → MxLy → absorbance
․ plot → figure 24-15 → x-axis
→ volume fraction → y-axis (A)
․ 2 straight line intersect → obtain
→ VM/VL ratio = 0.33/0.66 = ML2
Q : 問答題
請問 mole-ratio method
如何製備樣品？如何測得
實驗數據？如何作圖？如
何由圖得到結論？
(2)mole-ratio method (略)
․ prepare → series of solution
․ one reactant → constant conc.
․ other reactant → varied conc.
․ measure → MxLy → absorbance
․ plot f.24-16 → x-axis (mole ratio)
→ y-axis (A) → 2 straight line
․ if intersect = 1 : 1 → ML complex
․ if → 1 : 2 → ML2 complex
(3) slope-ratio method (略)
x M + y L ⇋ MxLy
＊ mass-balance expression
cM = [M] + x [MxLy]
cL = [L] + y [MxLy]
＊ cL >> cM → reaction (略)
→ shift to right
→ [M] << x [MxLy]
→ cM = x [MxLy]
→ A1 = ε b [MxLy] = ε b cM / x
→ plot → x - axis → cM
→ y - axis → absorbance (A1)
→ slope = ε b / x
＊ cM >> cL → reaction shift to right
→ [L] << y [MxLy] → cL = y [MxLy]
→ A2 = ε b [MxLy] = ε b cL / y
→ plot → x-axis → cL → y-axis
→ absorbance (A2) → slope = ε b / y
＊ ratio of slope → ε b / x ÷ ε b / y = y / x
→ obtain [MxLy]
24B Automated Photometry and
Spectrophotometry (略)
24C Infrared Absorption Spectroscopy
＊ IR instrument
→ dispersive ; Fourier-transform
＊ fig. 24-20 → 1200 ~ 3600 cm-1
→ functional group region
→ 600~1200 cm-1 fingerprint region
＊ table 24-5 → characteristic peak
Q : 圖表問答題 (figure 24-20)
․ 請問圖譜縱座標代表什麼意義？
橫座標代表什麼意義？
․ 何謂 functional group region？
有何應用價值？
․ 何謂 fingerprint region？
Q: 請問圖譜縱座標代表什麼意義？
橫座標代表什麼意義？
A: 縱座標 transmittance ( T ; T% )
P P
T = ; T% = 100%
P0 P0
UV/Vis. 縱座標 A = - logT = εbc
橫座標 cm =
-1 1/λ (每公分有幾個波)
IR frequency (ν) 1012 ~ 1014 Hz
wavelength (λ) 0.1 ~ 1000 nm
wavenumber (cm-1) 400 ~ 4000
Q : 何謂 functional group region？
A : 橫座標 > 1200 cm-1 的區域
可以判斷化合物的官能基結構
Q : 何謂 fingerprint region？
A : 橫座標 < 1200 cm 的區域
-1
可以作為化合物的指紋比對
Q : 圖表問答題
參考 Table 24-5，請說明由
表中可以得到哪些資訊？

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Chapter 24 Molecular Absorption Spectrometry Molecular Spectrometry Uv / Vis / Ir Widely Used Identification Inorganic Organic Biochemical Species

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Chapter 24 Molecular

＊ type of molecule absorb UV/Vis radiation

→ UV / Vis spectrometry application :

․ 24A-4 → spectrophotometric titration

․ 24A-5 → composition of complex ion

λmax , εmax ) 所代表的意義。

→ internal ox / red process

＊ table 24-3 → 圖表問答題

(A) (T) (P)

→ mixture solution → Bi3+; Cu2+

→ 2.0 x 10-3 M → Bi3+ / EDTA

→ complex first → not absorb

→ Cu2+ / EDTA→ abs. radiation

․ EDTA react with Bi3+ first

EDTA Bi3+ + EDTA → Bi3+/EDTA

Cu2+ Cu2+ + EDTA → Cu2+/EDTA

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