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(a)

Temperature programming in gas chromatography is performed by increasing the temperature of the column during the separation to raise analyte vapor Pressure and reduce retention times of late-eluting components. In this procedure, the solutes are strongly retained at the head of the column. Furthermore, as the temperature continue to increase, the solutes become less retained and are eluted which then emerge as sharp peaks.

Temperature limits in most gas chromatography columns indicate at which temperature the device must operate. Operating the column at the lower temperature limit may result to poor peak shape and other performance related complications. In terms of the upper temperature limit, two maximum values are considered. One is the isothermal temperature limit, which is the lower value, at which the column can be operated for extended durations. The upper value, the programmed temperature, is the condition at which the column should only be exposed for a few minutes at the end of a programmed temperature run. Decomposition of the stationary phase and "bleeding" of column can result from high temperatures. Peak broadening, tailing, and changing retention times are some indications of column degradation

(b).

Pressure programming in gas chromatography is executed by applying pressure control for the carrier gas. An increase in inlet pressure results to increase in mobile phase flow rate and reduction in retention time. Pressure programming can be used as an alternative to temperature programming to decrease the retention times of late-eluting components. In this procedure, the pressure can be quickly reduced to its initial value at the end of the run and be instantly ready for the next run. Thus, waiting for the hot column to cool down before the next process is not required. Furthermore, an advantage of programmed pressure is that is can be used for analytes that cannot withstand high temperatures.