Abstract: An apparatus for use in the performance of thin layer chromatography of the type which utilizes a thin bag as the developing chamber for the chromatogram is provided. The apparatus has a pair of substantially identical frames which hold the bag between the frames in a manner sealing the upper and lower ends of the bag while permitting sliding movement of the bag vertically within the frame. The frames are connected by a hinge which permits pivoting of the frames between an open and a closed position. In the closed position, the inner surfaces of the frame are aligned in a face-to-face relationship which accommodates the placement of the chromatography bag between the frames and holds the bag in an upright manner by frictional engagement of the bag with the inner surface of the frame. The bag is sealed by the action of outwardly extending ribs or a resilient pad presented on the inner surface of at least one of the upper and lower crossmembers of the frames.