Transcript File - Garbally Chemistry

Chromatography and
Instrumentation
Chapter 23
What is Chromatography?
• Chromatography is a separation technique
in which a mobile phase (water, ethanol)
carrying a mixture moves in contact with a
selectively absorbent (paper, alumna, silica
gel) stationary phase.
Paper
Chromatography
Method
a) A small amount of the mixture to be separated is placed on a strip of
chromatography paper.
b) The end of the paper is placed in a suitable solvent.
c) The solvent soaks up through the paper and dissolves the sample of
material being analysed. Each of the components of the mixture dissolves
to a certain extent. The least soluble come out of solution and appear as a
spot on the paper.
d) Thus the original sample will be split into its various component sat
different intervals along the paper.
Note: Avoid handling the paper as oils from the hands can affect the result.
Thin Layer Chromatography.
Stationary Phase -Thin layer of aluminium oxide or silica gel on a glass plate
or aluminium foil.
Method
A spot of the mixture been analysed is placed near the bottom of the plate. When
the spot is dried the TLC plate is placed standing in a suitable solvent.
TLC is more efficient than paper in that the particles in the stationary phase are
smaller and this gives better separation of components in the mixture.
Uses of TLC
 Pharmaceutical industry - to determine the purity of drugs.
 Forensic science-To separate the colours in dyes extracted from a crime scene.
 Analysis of drugs like cannabis
Under normal light
Under UV light. Note additional spots.
Column Chromatography
Stationary Phase-made into slurry using an appropriate solvent.
The mixture to be separated is dissolved in a solvent and added to the top
of the column.
The solvent is allowed to pass through the column and is kept moist. If the
column is long a series of coloured bands will appear along the column.
This series of bands is called column chromatography.
The procedure of passing a solvent through the column is called elution.
The general term for the solvent is the eluent.
Column Chromatography
Gas
Chromatography.
Mobile Phase=Inearth Gas(Argon, Nitrogen,Helium))
Stationary Phase= a high Boiling Point liquid spread on solid
particles(alumina)that are packed into a long coiled tube called the column. This
coiled tube of small diameter and several meters in length is kept inside a
temperature controlled oven.
Method
a) The sample is injected, vaporised, and carried through the tube using an inert
gas like Helium, Nitrogen, or Argon.
b) The various components in the mixture separate as they flow through the
column.
c) As each component leaves the column, it passes a detector which records a
signal.
Gas Chromatography.
Uses
 Level of alcohol in blood or Urine.
 Drug test athletes
GC-MS. Gas Chromatography + Mass Spectrometry.
 Each individual component analysed.


Analyse performance of drugs in body
Detect gases from waste dumps and organic pollutants in water.
A modern GC-MS instrument at
Tallaght R.T.C.
High Performance Liquid
Chromatography.
(HPLC)
• The substance to be analysed is added to a liquid solvent and
passed over a solid.
• Better separation if the particles in the stationary phase are very
small. A pump is used, therefore the column need not be as long
as in Gas Chromatography. Another advantage is that HPLC is
carried out at a lower temperature and can analyse compounds
that would decompose at a higher temperature.
High Performance Liquid Chromatography.
(HPLC)
Used
Analysis of foods- presence of growth promoters
- presence of additives
- Vitamins.
Mass Spectrometry
Mass Spectrometry (Francis William Aston)
- built to measure the masses of atoms.
- Detect the presence of Isotopes.
A Mass Spectrometer is used to
a. Identify the presence of Isotopes
b. Measure the relative abundance of isotopes
c. Measure relative atomic masses and relative molecular masses
d. Identify unknown compounds.
A Mass Spectrometer
How a spectrometer works.
1. Vaporisation
2. Ionisation
3. Acceleration
4. Separation
5. Detection
Uses of a Mass Spectroscope
• Used in conjunction with Gas Chromatography to detect banned drugs
in athletes.
• Test for drugs taken by drug addicts
• Analyse the gases in the tail of a comet.
UV spectrometry
• Used to detect the presence of certain functional
groups in molecules.
• Also used to detect or measure the concentration
of organic compounds in solution.
• Measure the amount of drug metabolite reaching a
certain part of then body.