ABSTRACT
The distribution coefficient of a solute can be changed during chromatographic development by either changing the composition of the mobile phase by gradient elution, or changing the free energy of the distribution system by temperature programming. Changing the temperature during chromatographic development is extremely effective in gas chromatography and thus is a very common development procedure. Solutes mixtures that contain components that have polar or dispersive interactions with the stationary phase of similar magnitude can usually be separated isothermally. A short isothermal period is often advisable to allow the elution process to stabilize before the temperature is raised. Flow programming in modern instrumentation is achieved by computer direction of the flow controller, however, the early flow programmers were mechanical in design. The technique of combined temperature and flow programming can ensure optimum chromatographic performance but requires considerable effort to arrive at the best parameters for each program.
