liquid chromatography

[ashvin]

I have read in books, that some times gradient runs are insrtument specific. Is it true? Why?

Regards
Ashvin

[skunked_once]

The reason has to do with the physical and mechanical configuration of each system. It depends on where in the system the solvents are mixed to form the gradient. Some systems use a separate pump for each mobile phase and the mixing takes place in a mixing chamber or at a "tee". Other systems mix the mobile phases at low pressure using a proportioning valve and them pump the mixed phase at high pressure through the column using a single pump. In every system, there is a certain amount of tubing between the point where the solvent is mixed and the column and this tubing volume (also including the injector) is different for every system. The result is that there is a time/volume delay from the point where the gradient is formed and actually reaches the column.