Piston movement control for preparative chromatography column

Abstract

In an axial-flow preparative chromatography column that contains a piston, commonly termed an adaptor, that is lowered over the top of the resin, the ability to lower the piston in a controlled manner to minimize the chances of damage to the resin is achieved by use of an aperture either in the piston head itself or in a compound bolt that secures the upper column frit to the piston head. The aperture is closed with a removable plug during storage and use of the piston head and column. During packing of the bed, however, the plug is replaced by a graduated rod operating as a dipstick to allow the operator to determine the distance between the bottom face of the piston head and the upper surface of the column packing.

1 . A compound bolt for securing a frit to a piston head in a preparative chromatography column, said compound bolt comprising:
 a hollow outer bolt having first and second ends;   a filler bolt insertable into said outer bolt and means for sealing said filler bolt inside said outer bolt to prevent fluid passage through said outer bolt; and   a rod insertable through said outer bolt when said filler bolt is not residing inside said outer bolt, said rod being of sufficient length to protrude beyond both said first and second ends of said outer bolt and bearing indicia such that the length of said rod protruding beyond said first end of said outer bolt is determinable by reading indicia on said rod protruding beyond said second end of said outer bolt.   
     
     
         2 . The compound bolt of  claim 1  further comprising an internal shoulder in said outer bolt positioned to abut an end of said filler bolt when said filler bolt is inserted in said outer bolt, and wherein said means for sealing said filler bolt is a gasket on said internal shoulder. 
     
     
         3 . The compound bolt of  claim 1  wherein said outer bolt has a threaded exterior and a threaded interior, and said filler bolt has a threaded exterior to mate with said threaded interior of said outer bolt. 
     
     
         4 . A method for lowering a piston head over a bed of particulate material in a preparative chromatography column, said method comprising:
 (a) with said piston head positioned above said bed but not in contact therewith and a hollow bolt securing a frit to a lower surface of said piston head, inserting a graduated rod through said hollow bolt until a lower end of said graduated rod contacts said bed, and observing indicia on said graduated rod exposed above said hollow bolt as an indication of the length of said graduated rod extending between said hollow bolt and said bed;   (b) removing said graduated rod;   (c) lowering said piston head by a selected distance related to said observed indicia; and   (d) inserting a plug in said hollow bolt in place of said graduated rod to seal said hollow bolt against entry of fluid.   
     
     
         5 . The method of  claim 4  wherein step (d) is performed prior to step (c). 
     
     
         6 . The method of  claim 4  wherein said plug is a filler bolt and said hollow bolt has an internal shoulder positioned to abut an end of said filler bolt, and step (d) further comprises compressing a gasket between said shoulder and said end of said filler bolt to seal said hollow bolt.