Patent ID: 7601265

Claim:
An apparatus for retaining magnetic particles within a segment of a flow-through cell during flow of a fluid through said cell comprising (a) an electromagnet comprising a winding connectable to a current source, said electromagnet having at least two poles separated by an air gap which is much smaller than the overall dimensions of the electromagnet, said air gap lying between the outer surfaces of the ends of said at least two poles, each of the latter outer surfaces comprising the outer surfaces of at least two cavities and of a tapered pole end part which separates said at least two cavities from each other, the cavities and the tapered end part of one of the poles being arranged substantially opposite to and symmetrically with respect to the corresponding cavities and tapered end part of the other pole of said at least two poles according to a symmetry axis which extends along a first direction, the depth of the air gap thereby varying at least along said first direction, said depth being measured along a second direction normal to said first direction, and said gap having at least a first symmetry axis which extends along said first direction; and (b) a flow-through cell which is suitable for receiving an amount of magnetic particles to be retained within a segment of the flow-through cell and to allow flow of a liquid through the flow-through cell along said first direction, and a portion of said flow-through cell being inserted in said air gap in such a way that at least one area of the outer surface of each of said tapered pole parts is in contact with or close to the outer surface of a wall of said flow-through cell and the length axis of said flow-through cell portion extends along said first direction.