most useful methods of analyzing chemicals on their basis of resolving multicomponent mixtures by

distribution between two phases, one stationary and the other mobile.  In the research relevant to this

text, the analysts performed vapor phase chromatography (gas-liquid).  When referring to vapor

phase chromatography, you will many times hear chemists use the term VPC.  In VPC, the stationary

phase is a high-boiling liquid (your sample) and the mobile phase is a gas (likely helium or nitrogen),

called the carrier gas.

     The most common methods of operating a GC, as experienced by this author, include injecting the

sample via syringe (usually 10-100 mL, depending on concentration of sample) through a septum into

the high temperature chamber (injection port) through which the inert carrier gas is flowing.  The

vaporized mixture is now swept by the carrier gas from the injection port onto the column.  When the

sample comes into contact with the column, the key stage of the separation has become initiated.

This process transpires because the stationary liquid phase in which the sample will dissolve and

partition with the mobile gas phase is physically and/or chemically bonded to inert packing (we refer

to it as the support) material contained in the column.  The success of the separation is also

dependent on the temperature of the column.  For example, column resolution degrades rapidly if the

entire column is not at the same temperature and most liquid mixtures will require oven temperatures

sufficient to maintain proper vapor pressures during the course of the separation.  Another important

parameter in successful separations is dependent on the flow rate of the carrier gas.  The rate must be

slow enough to allow equilibration between the phases, but sufficiently rapid to ensure that diffusion

will not overcome the resolution of the components.
 
     Once the sample has been injected into the injection port, the chemist must diligently observe the

computer terminal and watch for the initiation of a peak, signifying the sample is beginning to come

off the column.  Once a peak is observed to form, the chemist quickly covers the exit port with a

condensation tube (although a Pasteur pipet is sufficient).  The sample is then collected and ready to

analyze in its very pure form through other methods of analysis (NMR, UV-VIS Spectrophotometry,

¹³C).

     A typical Gas Chromatographer follows.  This GC is a GOW-MAC Chromatographer.  This

particular model, GOW-MAC Series 350, was used by this author extensively when research was

performed separating Entgegen (trans) and Zuzammen (cis) isomers from thio- and trifluoromethyl-

substituted cinnanamides.

     The following diagram entitled "Operation of a Gas Chromatographer" displays the operational

aspect behind the GC.  For a thorough description of each step, please refer above to "The function

and Operation of a Gas Chromatographer."

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