Abstract: An installation for the automatic preparation of specimens by liquid/solid extraction on a column is characterized in that the extraction device comprises, on either side of the columns (3), a valve (4) controllable to switch one column (3) to the other to actuate one column (3) adapted to ensure the extraction function when another column (3) is in a non-operating condition, each switching valve (4) being connected to a controllable common direction reversing valve (5) arranged to impose one direction of circulation on the fluid in anyone of the columns (3) of the extraction device and to ensure its return to the valve (5) to distribute the treated fluid toward a circuit selectively either for its rejection or for its analysis.