680 Fermentation and biochemical engineering Handbook 5.0 CHEMICAL COMPOSITION The most widely used method for determining chemical composition is chromatography. Several categories have been developed depending upon the species being separated. These include gas chromatography and several varieties of liquid chromatography including low pressure(gel permeation) and high pressure liquid chromatography and thin layer chromatography The basic principle behind these is the separation of the constituents traveling through a porous, sorptive material such The degree of retardation of each molecular species is based on its particular affinity for the sorbent. Proper selection of the sorbent is the most critical factor in determining separation. Other environmental factors such as temperature and pressure also play a key role The chemical basis for separation may include adsorption, covalent bonding or pore size of the material Gas chromatography is used for gases and for liquids with relatively low boiling points. Since many of the constituents in a biochemical reaction are of considerable molecular weight, high pressure liquid chromatography is the most commonly used. Specialized apparatus is needed for performing his analysis since chromatograph pressures can range as high as 10, 000 psi Thin layer chromatography requires no pressure but instead relies on the capillary action of a solvent through a paper-like sheet of sorbent. Each constituent travels a different distance and the constituents are thus separated Analysis is done manually, typically using various coloring or fluorescing Gel permeation chromatography utilizes a sorbent bed and depends on gravity to provide the driving force but usually requires a considerable time to effect a separation All of these analyses are typically performed in a laboratory; therefore hey require the removal of samples. As the reaction is conducted in a sterile environment, special precautions and sample removal procedures must be utilized to prevent contaminating the contents of the reactor 6.0 DISSOLVED OXYGEN Dissolved oxygen is one of the most important indicators in a fermen ss. It determines the potential for growth. The measurement of dissolved oxygen is made by a sterilizable probe inserted directly into the aqueous solution of the reactor. Two principles of operatic680 Fermentation and Biochemical Engineering Handbook 5.0 CHEMICAL COMPOSITION The most widely used method for determining chemical composition is chromatography. Several categories have been developed depending upon the species being separated. These include gas chromatography and several varieties of liquid chromatography including low pressure (gel permeation) and high pressure liquid chromatography and thin layer chromatography. The basic principle behind these is the separation ofthe constituents traveling through a porous, sorptive material such as a silica gel. The degree of retardation of each molecular species is based on its particular affinity for the sorbent. Proper selection of the sorbent is the most critical factor in determining separation. Other environmental factors such as temperature and pressure also play a key role. The chemical basis for separation may include adsorption, covalent bonding or pore size of the material. Gas chromatography is used for gases and for liquids with relatively low boiling points. Since many of the constituents in a biochemical reaction are of considerable molecular weight, high pressure liquid chromatography is the most commonly used. Specialized apparatus is needed for performing this analysis since chromatograph pressures can range as high as 10,000 psi. Thin layer chromatography requires no pressure but instead relies on the capillary action of a solvent through a paper-like sheet of sorbent. Each constituent travels a different distance and the constituents are thus separated. Analysis is done manually, typically using various coloring or fluorescing reagents. Gel permeation chromatography utilizes a sorbent bed and depends on gravity to provide the driving force but usually requires a considerable time to effect a separation. All of these analyses are typically performed in a laboratory; therefore they require the removal of samples. As the reaction is conducted in a sterile environment, special precautions and sample removal procedures must be utilized to prevent contaminating the contents of the reactor. 6.0 DISSOLVED OXYGEN Dissolved oxygen is one of the most important indicators in a fermen￾tation or bioreactor process. It determines the potential for growth. The measurement of dissolved oxygen is made by a sterilizable probe inserted directly into the aqueous solution ofthe reactor. Two principles of operation