To economically perform preparatory chromatography, a plurality of pumps
each having a corresponding one of a plurality of pistons and a
corresponding one of a plurality of cylinders are driven by one motor to
draw and pump solvent simultaneously into corresponding columns. To form
a gradient, the pumps are connected to two-way valves that are connected
alternately to a first solvent and a second solvent, whereby the time
said valve is in a first position controls the amount of solvent drawn
from the first reservoir into said pumps and the amount of time in said
second position controls the amount of said second solvent drawn from the
second reservoir into said pumps and the solvent is mixed in the pumping
systems. The detectors are photodiodes mounted to light guides in the
flow cells that generate signals related to light absorbance and
communicate with a controller, whereby the controller receives signals
indicating solute between the light guides and causes collection of
solute. An over-pressure system compensates for pressure over a
predetermined level.