Abstract A fractional-fill pipette assembly adapted to fill to a predetermined mark to obtain a desired known volume of liquid such as blood, plasma, test reagents or the like is disclosed. A means formed of a hydrophobic material is positioned within the tube bore, a predetermined distance from one end thereof so as to divide the capillary tube into two segments, one of the segments having a precise known volumetric capacity for collecting a desired known volume of liquid so that when the liquid fills the segment containing the precise known volume the liquid contacts the hydrophobic means defining the interface between the segments, the hydrophobic means breaks or resists the forces acting on the liquid filling the bore and prevents liquid from filling the pipette beyond the hydrophobic means by maintaining the surface tension of the liquid at the interface between the fluid and the hydrophobic means.
The fractional-fill pipette assembly of claim 1 wherein said hydrophobic means is formed of plastic.
Claim 2
Dependent Claim
17 words
The fractional-fill pipette assembly of claim 1 wherein said hydrophobic means is coated with a hydrophobic material.
Claim 3
Dependent Claim
56 words
The fractional-fill pipette assembly of claim 1 wherein said hydrophobic means is a tubular member made of molded plastic, said member having a zone of increased diameter slightly greater than the bore diameter of the capillary so as to provide an interference fit in the capillary after being positioned a predetermined distance from said one end.
Claim 4
Dependent Claim
25 words
The fractional-fill pipette assembly of claim 1 wherein said capillary assembly includes a holder slidably mounted on said capillary and positioned between the ends thereof.
Claim 5
Dependent Claim
54 words
The fractional-fill pipette assembly of claim 5 wherein said holder comprises an integrally molded plastic body including a sleeve having a passage therethrough, said passage having a zone where the diameter is substantially equal to the outer diameter of the capillary tube so that when slidably mounted in position an interference fit is formed.
Claim 6
Dependent Claim
56 words
The fractional-fill pipette assembly of claim 1 wherein said hydrophobic means is a tubular member made of a molded plastic material having a central zone, the outside diameter of which is slightly greater than the bore diameter of the capillary tube and extending from said zone is at least one frustro conical cone integrally formed therewith.