1. Molecular Absorption Spectroscopy

2. Molecular Spectroscopy
(based on ultraviolet, visible, and infrared radiation)
The identification and determination of a number of inorganic, organic, and biochemical species.

3. Ultraviolet/visible absorption spectroscopy  primarily for quantitative analysis
Infrared absorption spectroscopy  for determining the structure of both inorganic and organic compounds

4. Ultraviolet and Visible Molecular Absorption Spectroscopy
1. absorbing species.
Absorption of u.v/visible radiation by molecules.
Band
the transition of an electron from the ground state to one of the many vibrational and rotational energy states of excited electronic energy state.

5. Solvent effect
A in B solvent A in C solvent

6. Absorption by organic compounds
1) Absorption of radiation by organic molecules ( nm) : results from interactions between photons and those electron in bond.
2) The wavelength depends on how tightly its several electrons are bound.

7. The shared electrons in single bond(C-H, C-C)  vacuum ultraviolet region(below 180nm)  Single bond spectra not widely used for analytical purpose  quartz and atmospheric components absorb in this region (It require the evacuated spectrophotometer with lithium fluoride optics).

8. 4) Electrons in double and triple bonds of molecules  easily excited  species with unsaturated bonds generally exhibit useful absorption peaks.

9. 5) Unsaturated organic functional group that absorb in the u. v
5) Unsaturated organic functional group that absorb in the u.v. or visible region chromophores.
6) Saturated organic compounds containing heteroatoms (oxygen, nitrogen, sulfur or halogen) contain nonbonding electrons (excited by radiation in the nm range)

10. Absorption by inorganic species.
The ions and complexes of elements in the first two transition series absorb broad bands of visible radiation  transitions between filled and unfilled d-orbitals.

11. Charge-Transfer Absorption
For quantitative purpose, charge-transfer absorption is important due to large molar absorptivities(>10,000)  High sensitivity
ex) A charge- transfer complexes.
 phenolic complex of iron(III),
the 1,10-phenanthroline complex of iron(II)

12. 2. Typical Instrument.
Spectrophotometer : a grating or a prism monochromator
advantage  the wavelength used can be varied continuously  obtain entire absorption spectra.

13. Photometer : an absorption filter or an interference filter
advantage  low cost, simplicity, ruggedness, portability, and ease of maintenance
disadvantage  less versatility, their inability to generate entire spectra.

14. Figure 1. Single-beam photometer for absorption measurements in the visible reion.

15. * Uitraviolet/Visible Spectrophotometers
Single-Beam Instrument
(spectronic 20)
2) Double-Beam Instrument
3) Multichannel

16. Single-Beam Instrument (spectronic 20)
The spectral range : nm
Effective bandwidth: 20 nm
For quantitative absorption measurement at a single wavelength
Advantage: simplicity, low cost, ease of maintenance
Instruments range from 190 ( 210) nm to 800 (1000) nm

17. Figure 2. Its optical diagram.
(Courtesy of Milton Roy Company, Analytical Products, Rochester, NY)

18. Figure 3. A double-beam recording spectrophotometer for the ultraviolet and visible regions; the Perkin-Elmer Series.
(Courtesy of Coleman Instruments Division, Oak Brook, IL )

19. Multichannel Instrments
Multichannel, or diode array, spectrometers are products of modern optoelectronic technology
It makes it possible to record an entire ultraviolet or visible spectrum rapidly.
All wavelengths can be monitored simultaneously and data for an entire spectrum collected in a second or less

20. Figure 4. Diagram of a multichannel spectrophotometer based on a grating and photodiode detector.

21. 3. Qualitative Application of UV/Vis Spectroscopy
; Ultraviolet spectra lack sufficient fine structure to allow unambiguous identification of an analyte.
Solvent
- A solvent for uv/vis spectroscopy must be transparent and should dissolve a sufficient quantity of the sample.

22. -Polar sovent(water, alcohols and ketone) tend to obliterate vibration spectra.
Nonpolar solvents(cyclohexane) provide better spectra
The polarity of the solvent often influences the position of absorption maxima.

23. 4. Quantitative Application of UV/Vis Spectroscopy
- One of the most useful tools for quantitative analysis
Wide applicability : Enormous numbers of inorganic, organic, and biochemical species
High sensitivity : Typical detection limit M

24. 3) Moderate to high selectivity
4) Good accuracy : the relative error range 1% - 5%
5) Ease and Convenience
<Procedure detail>
Spectrometric analysis
: yield a reproducible relationship between absorbance and analyte concentration.

25. Wavelength selection
Variables that influence absorbance
Cleaning and handling of cells
Determination of the relationship between absorbance and concentration.

26. Standard Addition method
Adding one or more increments of a standard solution to sample aliquots of the some size
Each solution is then diluted to a fixed volume before measuring its absorbance.

27. ex)
* Several identical aliquots Vx of the unknown solution with a concentration Cx  transferred to volumetric flask having a volume Vt
* To each of these flask is added a variable volume Vs mL of a standard solution of the analyte(concentration Cs)
* Each solution is diluted to volume.

28. A plot of As as a function of Vs
straight line of the form
As = mVs + b (m: kCs, b=kVxCx)

29. * In the interest of saving time and sample, it is possible to perform a standard addition analysis using only two increments of sample.  A single addition of Vx mL of standard would be added to one of the two sample.

30. Analysis of Mixture
: The total absorbance of a solution at any given wavelength is equal to the sum of the absorbance of the individual components in the solution

31. 5. Photometric and Spectrophotometric Titration
- Useful for locating the equivalence points of
titration
The application of absorption
Require that one or more of the reactants or
product absorb radiation
Titration Curve
- A plot of absorbance as a function of titrant volume.

32. · Each molecular species has a unique infrared
Infrared Absorption Spectroscopy
IR Spectrophotometry
 One of the most powerful tools for identifying
pure organic and inorganic compounds
because almost all molecular species absorb
infrared radiation
· Each molecular species has a unique infrared
absorption spectrum.
· The identification of an analyte
By an exact match between the spectrum of a
compound of know structure and that of an
analyte.

33. · a typical infrared spectrum for a liquid consists of
1. I.R Absorption Spectrum
Vibrational absorption occurs in the infrared region
with liquid or solid ( rotation is often hindered
or prevented thus, the effects are not detected.)
· a typical infrared spectrum for a liquid consists of
a series of vibrational peaks
2. Instrumentation for IR spectroscopy
· Three type of I.R
Dispersive spectrometer
r.s
sample
monochromator D

34. · Disadvantage ; the complexity of the instruments and their high cost
· Advantage ; any scattered radiation generated in the cell compartment is largely removed by monochromator
2) Fourier- transform(FT-IR) spectrometer
· Advantage ; Unusually high sensitivity, resolution and speed of data acquisition
· Disadvantage ; the complexity of the instruments and their high cost
· No dispersing element.
all wavelength are detected and measured
simultaneously

35. · To separate wavelengths
It is necessary to modulate the source signal in such a way that it can subsequently be decoded by a Fourier Transformation, a mathematical operation that require a high-speed computer.
3) Filter photometer
Monitoring the concentration of air pollutants such as carbon monoxide, nitrobenzene, vinyl chloride and pyridin
= Interference filter

36. 3. Qualitative Application of I.R
Peaks useful for the identification of functional
groups (in the shorter wavelength region of the
infrared)
Identification of the functional groups in a
molecules is seldom sufficient to permit
positive identification of the compound
The entire spectrum from 2.5 to 15 µm must
be compared with that of known compounds.

37. · I.R cells are required to permit the transmission of
4. Quantitative Infrared photometry
and spectophotometry
· I.R cells are required to permit the transmission of
measurable intensities of radiation through pure
samples or very concentrated solution of analyte.
· Measurements of dilute analyte solutions are
frequently precluded by the lack of good solvents
that transmit over appreciable regions of the
infrared spectrum
· A reference absorber is often dispensed with
entirely In qualitative infrared work.

38. · Applications of quantitative I.R spectroscopy
- IR ; Potential for determining an unusually large
number of substances because nearly all
molecular species absorb in this region.
- The uniqueness of an infrared spectrum provides a
degree of specificity
- The specificity has particular application to the
analysis of mixtures of closely related organic
compounds
Government regulations
The variety of atmospheric pollutants can be determined
with a simple, portable filter photometer equipped with a
separate interference filter.