Locking pipette tip and mounting shaft

A pipetting system comprising:

• a disposable pipette 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 lower end of the collar having an inside diameter larger 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 tip mounting shaft having:
• a locking section including a stop that engages a circumferential shelf of the 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 an 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 to the mounting shaft;
• and
• an annular groove with a sealing ring located in the annular groove, wherein the sealing ring on the mounting shaft engages the inside surface of the pipette tip when the mounting shaft is fully inserted into the pipette tip.

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 circumferential sealing ring extending inward from the inside surface of 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;
• and
• a lower section with a frustoconical portion located below the locking section, wherein said frustoconical portion area of the mounting shaft provides an interference fit with the circumferential sealing ring on the pipette tip when the mounting shaft is inserted into the pipette tip, the height of the frustoconical portion accommodating a range of vertical travel for interfering engagement of the circumferential sealing ring on the pipette tip against the tip mounting shaft before full engagement of the stop on the mounting shaft against the shelf of the pipette tip.