1. Chapter 20
Atomic Spectroscopy

2. ATOMIC SPECTROSCOPY
By exposing these atoms to temperature they are able to “jump” to high energy levels and in return, emit light.
Atomic “absorption” is the absorption of light by free atoms.
An atomic “absorption” spectrophotometer is an instrument that uses this principle to analyze the concentration of metals in solution.
Atomic “Emission” Spectroscopy
No lamp required.
Light emitted by hot atoms where electrons promoted excited states in the flame.

3. Absorption promotes electrons from their ground state to higher-energy excited state.

4. How Temperature Affects Atomic Spectroscopy
Boltzmann Distribution (Math!)
Consider molecule with two energy levels
Atoms/molecules can have more than one state at a given energy.
This is called Degeneracy, labeled as “g”

5. ATOMIC SPECTROSCOPY
Flame Emission and Atomic Absorption Spectroscopy (3 main types)
Atomic Emission (with thermal excitation), AES
Atomic Absorption, (with optical photon unit) AAS
Atomic Florescence, AFS
Three types of high-temperature plasmas
The inductively coupled plasma (ICP).
The direct current plasma (DCP).
The microwave induced plasma (MIP).

6. ATOMIC SPECTROSCOPY Advantages of AAS Determination of 68 metals
Ability to make ppb determinations on major components of a sample
Precision of measurements by flame are better than 1% rsd.
Sample preparation is simple (often involving only dissolution in an acid)
Instrument easy to tune and operate

7. ATOMIC SPECTROSCOPY Elements that are highlighted in pink are detectable by AAS

8. Atomic Spectroscopy
The light that is focused into the flame is produced by a hollow cathode lamp. Inside the lamp is a cylindrical metal cathode containing the metal for excitation, and an anode. When a high voltage is applied across the anode and cathode, the metal atoms in the cathode are excited into producing light with a certain emission spectrum.

9. Atomic Spectroscopy
The type of hollow cathode tube depends on the metal being analyzed. For analyzing the concentration of copper in an ore, a copper cathode tube would be used, and likewise for any other metal being analyzed. The electrons of the atoms in the flame can be promoted to higher orbitals for an instant by absorbing a set quantity of energy (a quantum).

10. Atomic Spectroscopy
This amount of energy is specific to a particular electron transition in a particular element. As the quantity of energy put into the flame is known, and the quantity remaining at the other side (at the detector) can be measured, it is possible to calculate how many of these transitions took place, and thus get a signal that is proportional to the concentration of the element being measured.

11. Atomic Spectroscopy Atomic “Absorption” Spectroscopy
frequency is passed through flame. Intensity of transmitted radiation is measured.

12. Atomization: Flames, Furnaces, and Plasmas
Use a premix burner
Sample, oxidant, and
fuel are mixed before
going into flame

13. Atomization: Flames, Furnaces, and Plasmas
Graphite furnace
Provide greater sensitivity
Requires less sample to analyze
Sample injected into L’vov
platform. Contact with
heated platform atomizes

14. Atomization: Flames, Furnaces, and Plasmas
Ar gas + analyte fed into torch
Tesla coil ionizes Ar gas
Free electrons accelerated by radio freq. superheat gas to 6 – 10K Kelvin by colliding with atoms.

15. Atomization: Flames, Furnaces, and Plasmas
Nebulizer/Atomizer
Makes analyte into a fine mist used for testing

16. How Temperature Affects Atomic Spectroscopy
Examples!
The lowest excited state of a sodium atom lies 3.371E-19 J/atom above the ground state.
Degeneracy of the excited state is 2.
Ground state degeneracy is 1.
Calculate the fraction of Na atoms in the excited state in an oxyacetylene flame at 2600 K:
What if 2610 K?

17. Physical separation of a mixture into its individual components.
Chromatography
Physical separation of a mixture into its individual components.

18. Chromatography From Wikipedia ...
Chromatography (from Greek word for chromos for colour) is the collective term for a family of laboratory techniques for the separation of mixtures. It involves passing a mixture which contains the analyte through a stationary phase, which separates it from other molecules in the mixture and allows it to be isolated.

19. How Does Chromatography Work?
In all chromatographic separations, the sample is transported in a mobile phase. The mobile phase can be a gas, a liquid, or a supercritical fluid.
The mobile phase is then forced through a stationary phase held in a column or on a solid surface. The stationary phase needs to be something that does not react with the mobile phase or the sample.
The sample then has the opportunity to interact with the stationary phase as it moves past it. Samples that interact greatly, then appear to move more slowly. Samples that interact weakly, then appear to move more quickly. Because of this difference in rates, the samples can then be separated into their components.

20. How Does Chromatography Work?

21. How Does Chromatography Work??
Greater separation occurs with:
–greater number of theoretical plates (N)
–as plate height (H or HETP) becomes smaller
L = N H or H = L / N
where L is length of column, N is number
of plates, and H is height of plates or height equivalent to theoretical plate (HETP)

22. Plate Theory - Martin & Synge 1954 Nobel Laureates
View column as divided into a number (N)
of adjacent imaginary segments called
theoretical plates
Within each theoretical plate analyte(s) completely equilibrate between stationary phase and mobile phase
Column
Theoretical plate

23. Chromatographic principle
Stationary phase
Mobile phase
Sample
mixture
Equilibrium establishes at each point (ideally)
The molecules of the mixture interact with the molecules of the Mobile and Stationary Phase
Retardation of rate of movement of molecules
Each molecule interacts differently with MP and SP
Different distribution coefficients and different net rates of migration

24. Plate Theory – Practical Considerations
• It is not unusual for a chromatography column
to have millions of theoretical plates
• Greater separation occurs with:
–greater number of theoretical plates (N)
–as plate height (H or HETP) becomes smaller
L = N H or H = L / N
where L is length of column, N is number
of plates, and H is height of plates or height equivalent to theoretical plate (HETP)

25. Plate Theory – Practical Considerations
Greater separation occurs with:
–greater number of theoretical plates (N)
–as plate height (H or HETP) becomes smaller
L = N H or H = L / N
where L is length of column, N is number
of plates, and H is height of plates or height equivalent to theoretical plate (HETP)

26. Basics of Chromatography
Separation of Analytes
Type of Equilibrium

27. Basics of Chromatography
Average linear flow rate
Average linear flow of mobile phase

28. Types of Chromatography
Liquid Chromatography
Used to identify unknown plant pigments & other compounds.
Paper Chromatography
Can be used to separate the components of inks, dyes, plant compounds (chlorophyll), make-up, and many other substances
Thin-Layer Chromatography
Uses thin plastic or glass trays to identify the composition of pigments, chemicals, and other unknown substances.
Gas Chromatography
Used to determine the chemical composition of unknown substances, such as the different compounds in gasoline shown by each separate peak in the graph below.

29. Principle and Instrumentation of GC

30. Principle and Instrumentation of GC
The volatile sample in the liquid matter is injected to the column.
The temperature of column is setted in which sample can be vaporized.
The gas is pumped and then it carries the sample (gas) through the column.
The sample which has higher boiling point/melting point will be retained by column, in contrast the lower one will be carried through the column faster.
Means the higher b.p/m.p wil be lower the Rt and vice versa