Preparative LC prepares samples for the next step. Whether it is identification by i.e. NMR or purifying for testing, preparative LC is used to separate components for further use.
Depending on the application the preparative LC system can be an analytical system with a fraction-collector producing µgrams to a pilot scale system producing grams of desired component in your sample. Each application has its own parameters to take into account; injection volume, flow, gradient vs. isocratic, column material, column dimensions and so on. In most cases analytical LC methods are available and are used to scale up to preparative LC.
From analytical scale to pilot scale, JSB can get your purification running.