Chapter 5Chapter 5Ultraviolet and Visible Ultraviolet and Visible

SpectrophotometrySpectrophotometry

5.1. Concepts of UV-Vis.UV-Vis.Spectrophotometry

5.2. UV-Vis. UV-Vis. Spectrophotometer

5.3. Analytical Methods

5.1. Concepts of UV-Vis. UV-Vis. Spectrophotometry

1. Molecular absorption and Fluorescence

2. Lambert-Beer’s Law

(1)Transmittance T:

KbCPP eT 0

(5.1)

(2) Absorbance:

bCKp

pTA 4343.0lglg 0

(3) Molar absorptivity

When: the unit of b is in cm , C in mol/L,

molar absorptivity is:

BKv201087.04343.0

B:transition probability, : effective area of molecular

(5.2)

(5.3)

5.2. 5.2. UV-Vis. SpectrophotometerUV-Vis. Spectrophotometer

AA SpectrophotometerSpectrophotometer

Double beanDouble beanUV-Vis. SpectrophotometerUV-Vis. Spectrophotometer

5.3. Analytical Methods

1. Qualitative Analysis

2. Quantitative Analysis

3. Dual wavelength Spectrophotometry

4. Differential Spectrophotometry

5. Derivative Spectra

1. Qualitative Analysis

Organic Compound⑴

Chromophore

max(nm) (mol-1.cm-

1)

Transition Type

R3 C—N — 200 3000 n→*

R3 C—S — 200 2000 n→*—N=N — 340 10 n→ *

—S —S — 250-330 1000 n→*

R2 C=S 5 0 0,2 4 0 10,9000 n→ *

R2 C=O 2 8 0,1 9 0 20,2000 n→*, n→ *—COOR 205,165 50,4000 n→ *, → *

⑵Inorganic Compound

Ion n3d,emax(nm) Ion n3d,e

max(nm)

Sc2+ 0 ------ Zn2+ 10 ------

Ti(H2O)63+ 1 492.6 Cu+ 10 ------

VO2+ 1 625 Cu(H2O)62+ 9 592,794

Cr (H2O)63+ 2 407,575 Ni(H2O)6

2+ 8 395,650,740

V (H2O)62+ 3 557 Co(H2O)6

2+ 7 516,541,625

Cr (H2O)62+ 3 709 Fe(H2O)6

3+ 5 411,540,794

Mn (H2O)63+ 4 476 Mn(H2O)6

2+ 4 402,435,532

3. Double wavelength Spectrophotometry

Two-component analysis with double wavelength

AC,520 = AC,540

AB+C,520 = AB,520 + AC,520

AB+C,540 = AB,540 + AC,540

A = AB+C,520 - AB+C,540

= AB,520 - AB,540

4. Differential Spectrophotometry

1,2,

1,,

ss

sxxd TT

TTT

1,1,,2,, ssxdsxdx TTTTTT

(5.4)

(5.5)

⑴⑴when Twhen TSS,,11=0,T=0,TSS,,22=100%=100%

⑵⑵when Twhen TSS,,11=0,T=0,TSS,,22<100%<100%

⑶⑶when Twhen TSS,,11>0>0

xxdx lcAA ,

xsxdx lcAAA 2,,

x

ssxdsxd

xx

lc

TTTTT

TA

)lg(

lg

1,1,,2,,

(5.6)

(5.7)

(5.8)

5. Derivative Spectra5. Derivative Spectra

5.4 Molecular Fluorescence Spectrometer