Locking pipette tip and mounting shaft

1. A pipetting system comprising:

a disposable pipette tip having

a barrel with a lower opening through which liquid is aspirated into the barrel and dispensed from the barrel,

a collar having an upper opening for receiving a pipette tip mounting shaft, the inside surface of the collar including a substantially circumferential locking element extending inward from the inside surface of the collar, and the lower end of the collar having a larger inside diameter than the inside diameter at the upper end of the barrel, and

a circumferential shelf that connects the lower end of the collar to the upper end of the barrel; and

a pipette mounting shaft including

a lower sealing section; and

an upper locking section, the locking section of the mounting shaft including a stop that engages the shelf of a pipette tip when the mounting shaft is fully inserted into the collar of the pipette tip, two or more outwardly extending lobes spaced circumferentially around the locking section of the mounting shaft and located above the stop on the mounting shaft for engaging the locking element on the inside surface of the collar, and recessed relief portions in the upper locking section of the mounting shaft spanning circumferentially between the lobes and recessed relative to the lobes such that the collar distorts outwardly at the lobes and inwardly at the relief portions when the pipette tip is locked on the mounting shaft over the stop and the lobes; and

wherein a circumferential portion of the lower sealing section of the mounting shaft engages the upper end of the tip barrel to seal the tip barrel against the mounting shaft when the tip collar is locked onto the mounting shaft over the stop and lobes.

2. The pipetting system as recited in claim 1 wherein:

the pipette tip barrel includes a circumferential sealing ring extending inward from an inside surface of the tip barrel below the circumferential shelf; and

the lower sealing section on the mounting shaft engages the circumferential sealing ring when the mounting shaft is fully inserted into the pipette tip.

3. The system as recited in claim 1 wherein the circumferential shelf on the pipette tip extends continuously around the inside circumferential surface of the pipette tip.

4. The system as recited in claim 1 wherein the substantially circumferential locking element on the pipette tip is located below a rim of the upper opening of the collar of the pipette tip.

5. The system as recited in claim 1 wherein the pipette tip barrel includes a frustoconical portion.

6. The system as recited in claim 5 wherein the lower sealing section on the mounting shaft is frustoconical.

7. The system as recited in claim 1 wherein each lobe includes an inclined ramp portion that facilitates distortion of the pipette tip collar as the mounting shaft is inserted into the pipette tip.

8. The system as recited in claim 1 wherein the mounting shaft has at least three lobes.

9. The system as recited in claim 1 wherein the substantially circumferential locking element on the pipette tip is a substantially circumferential locking ring with a void that provides an opening that vents when the pipette tip is fully mounted on the mounting shaft.

10. The pipetting system as recited in claim 1 wherein the circumferential shelf of the pipette tip reduces the bore diameter of the pipette tip by about 0.004 to 0.040 inches.

11. A pipetting system as recited in claim 1 wherein the lower sealing section on the mounting shaft that is substantially cylindrical and the area at the upper end of the pipette tip barrel where the tip seals against the mounting shaft is substantially cylindrical as well.

12. A pipette system as recited in claim 1 wherein the stop on the mounting shaft is an angular step between the locking section and the lower sealing section.

13. A pipette system as recited in claim 1 wherein the stop on the mounting shaft is immediately below and adjacent a cylindrical stabilizing section on the mounting shaft having a diameter greater than the diameter of the mounting shaft below the stop which engages the pipette tip collar above the circumferential shelf of the pipette tip when the mounting shaft is fully inserted into the pipette tip.

14. A pipetting system as recited in claim 1 wherein the system includes multiple pipette mounting shafts each in accordance with the limitations recited in claim 1 for the pipette mounting shaft.

15. A pipetting system comprising:

a disposable pipette tip having

a barrel with a lower opening through which liquid is aspirated into the barrel and dispensed from the barrel;

a collar having an upper opening that receives a lower end of a pipette mounting shaft, a lower end of the collar having a larger inside diameter than the inside diameter of the upper end of the barrel; and

a circumferential shelf that connects the lower end of the collar to the upper end of the barrel; and

a pipette mounting shaft including

an upper locking section, the locking section of the mounting shaft including a stop that engages the circumferential shelf of the pipette tip when the mounting shaft is fully inserted into the collar of the tip, two or more outwardly extending lobes spaced circumferentially around the locking section of the mounting shaft and located above the stop on the mounting shaft for engaging the inside surface of the collar, and recessed relief portions in the upper locking section of the mounting shaft spanning circumferentially between the lobes and recessed relative to the lobes such that the collar distorts outwardly at the lobes and inwardly at the relief portions when the pipette tip is fully mounted on the mounting shaft.