In gas chromatography, when the temperature is programmed to increase during the separation, it is called temperature programming.

Here's why:

* Isothermal: The temperature is held constant throughout the entire separation. This is suitable for analyzing samples with components that have similar boiling points.

* Temperature Programming: The temperature is increased linearly or in steps over time. This is useful for separating complex mixtures with a wide range of boiling points. The increasing temperature helps to elute higher boiling point components more quickly, improving separation efficiency.

Let me know if you have any other questions!