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

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.

Soxhlet Extraction

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.

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.

Chromatography

Characteristics of Different Chromatographic Techniques

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).

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…

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.

Ion-Exchange Chromatography (2)

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.

Chromatography