Patent ID: 7318911

Claim:
A pipette tip in combination with a pipetter, said combination comprising: a pipette tip for attachment to said pipetter having a suction device communicating through a pipetter barrel, the suction device having displacement sufficient to draw a first volume of fluid into the pipette tip; the pipette tip having an apex end opening for drawing said fluid into the pipette tip, an enlarged upper end for attachment to the pipetter barrel in an airtight relationship, and a pipette tip cavity defining a retaining volume between the apex end and the pipetter barrel; means for attachment of the pipette tip to the barrel of the pipetter at said enlarged upper end; a first filter membrane permeable to sterile ultrapure air spaced a predetermined distance from the pipetter barrel to divide the retaining volume of the pipette tip cavity into an upper volume and a remaining volume; a second filter membrane permeable to fluid spaced from the first filter membrane to divide the remaining volume of the pipette tip cavity into a middle volume and a lower volume: the sum of the middle volume and the lower volume being greater than the first volume of fluid whereby fluid drawn into the pipette tip does not contact the first filter membrane a cone mounted to the inside of the apex end of the pipette tip cavity, the cone moveable by said fluid entering the pipette tip and seating to close the pipette tip when said fluid is within the pipette tip cavity; and, means on the cone for mounting the second filter membrane.