Patent ID: 7094352

Claim:
A column comprising a first end ( 2 a ) provided with means to added media particles, and a second end ( 2 b ) provided with a fluid collection means for collecting fluid from over some or all of the internal cross-section of the column, wherein said first and second ends ( 2 a , 2 b ) are held apart by a column wall, and wherein said second end ( 2 b ) is provided with blocking means ( 52 , 72 , 82 , 92 , 102 ) movable between a blocking position where said blocking means ( 52 , 72 , 82 , 92 , 102 ) substantially obstructs the collection of fluid from a predetermined portion (CR, CR 1 , CR 2 ) of the cross-section of the column while permitting the collection of fluid from another portion of the cross-section of the column, and a non-blocking position where it does not substantially obstruct the collection of fluid from the predetermined portion (CR, CR 1 , CR 2 ) of the cross-section of the column.