GC Temperature Programming

Temperature is one of the two most important variables in GC and affects the retention, selectivity, and to a lesser extent the efficiency of all separations. As temperature is convenient to manipulate within a GC experiment, and as it has a large effect on the selectivity (and hence resolution) of a separation, it is a primary variable in method development and optimization. The aims of this module include illustrating the relationship between temperature and retention in GC, and highlighting the advantages and disadvantages of isothermal and temperature programmed GC separations. The theory behind temperature programmed GC and several useful rules of thumb is discussed, as well as the usefulness and optimization of scouting temperature programs for GC method development.

At the end of this section you will be able to recognize the advantages and disadvantages of using temperature programmed GC, explain how to implement a scouting temperature program for an unknown sample, make decisions on whether samples can be run isothermally or need a temperature program, suggest reasonable isothermal temperatures, develop a temperature program for an unknown sample, and optimize the separation obtained from the temperature program suggested.

Topics include:

• The role of temperature in GC separations
• Isothermal and gradient temperature GC
• Theory of temperature programmed GC
• Scouting temperature programs
• Optimizing isothermal conditions
• Initial temperature and hold times
• Adjusting the ramp rate
• Mid-ramp holds
• Peak capacity
• Final temperature and time