Topics - Temperature Programmed
Temperature programming is a chromatography development technique used largely in gas chromatography to accelerate the elution rate of late peaks that, otherwise, would take a very long time to elute. It is achieved by continuously raising the column temperature, usually as a linear function of time, during the elution process. The retention time of a solute is proportional to the distribution coefficient which, in turn, increases as the negative exponent of the standard energy of distribution divided by the product of the gas constant and the absolute temperature. The standard energy is equal to the sum of the standard enthalpy and the product of the standard entropy and the absolute temperature. It is seen that retention is a rather complex function of temperature. The net effect of temperature programming on solute elution is similar to the effect of gradient elution in liquid chromatography. In practice, program limits can be as low as 5o C and as high as 250o C and under certain circumstances even higher. Temperature programming is an essential feature in most gas chromatography analyses and so programming facilities are standard on virtually all gas chromatographs.