1. Basic Principles of Chromatography (2)
Food Analysis
Lecture 19 (4/5/2005)
Basic Principles of Chromatography (2)
Qingrong Huang
Department of Food Science
Read Material: Chapter 27, page 437
Final Exam: April 29

2. Extraction
Extraction: the transfer of a solute from one liquid phase to another.
Batch extraction: the solute is extracted from one solvent by shaking
it with a second immiscible solvent.
Continuous extraction: requires special apparatus like Soxhlet extractor.
Countercurrent extraction: a serial extraction process which separates
two or more solutes with different partition coefficients from each other
by a series of partitions between two immiscible liquid phases.

3. Soxhlet Extraction

4. Example of Soxhlet Extraction
Cereal fat extraction: - fat content is measured by weight loss of
the sample or by weight of fat removed.
Weigh, to the nearest mg, about 2g of predried sample into a
predried extraction thimble, with porosity permitting a rapid flow of
ethyl ether;
2. Weigh predried boiling flask;
3. Put anhydrous ether in boiling flask. Assemble boiling flask,
Soxhlet flask, and condenser;
4. Extract in a Soxhlet extractor at a rate of 5 to 6 drops per second
condensation for about 4hrs;
5. Dry boiling flask with extracted fat in an air oven at 100 °C for
30 mins, cool in desiccator, and weight.

5. Chromatography
Chromatography: a general term applied to a wide variety of separation
techniques based on the partitioning or distribution of a sample (solute)
between a moving or mobile phase and a fixed or stationary phase.
The relative interaction of a solute with these two phases is described by
the partition (K) or distribution (D) coefficient (ratio of concentration of solute
in stationary phase to concentration of solute in mobile phase).
The mobile phase may be either gas (GC), liquid (LC), and supercritical
Fluid.

6. Chromatography

7. Characteristics of Different Chromatographic Techniques

8. Physicochemical Principles
of Separation
Adsorption (solid-liquid) chromatography: oldest, Tsvet in 1903
The stationary phase is a finely divided solid (to maximize the
surface area),
The mobile phase can be either gas or liquid
The stationary phase (adsorbent) is chosen to permit differential
Interaction with the components of the sample to be resolved.
The interaction forces include:
- Van der Waals forces
- Electrostatic forces
- Hydrogen bonds
- Hydrophobic interactions
Typical stationary phases: silica (slightly acidic), alumina (slightly
Basic), charcoal (nonpolar).

9. Applications of Adsorption
Chromatography
Separate aromatic or aliphatic nonpolar compounds, such as lipids,
primarily according to the type and number of functional groups present.
Carotenoid pigments from plants;
Analysis of fat – soluble vitamins, etc…

10. Ion-Exchange Chromatography
Ion-exchange Chromatography: a separation/purification process
occurring naturally, e.g. in soils, and is utilized in water softeners and
deionization. Three types of separation:
Ionic from nonionic;
Cationic from anionic;
Mixtures of similarly charged species.
Similar to adsorption chromatography
nature of interactions - electrostatic
Cationic exchangers: contain covalently bound negatively charged
functional groups.
Anionic exchangers: contain bound positively charged groups.

11. Ion-Exchange
Chromatography (2)

12. Size-Exclusion Chromatography
(SEC)
SEC, also known as Gel Permeation Chromatography (GPC), can
be used for the resolution of macromolecules, such as proteins and
Carbohydrates, as well as for the fractionation and characterization
Of synthetic polymers.

14. Chromatography