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A disposable pipette tip having that is configured to mount on a tip mounting shaft having a locking section and a separate sealing section. The locking section has outwardly extending locking lobes circumferentially spaced around the mounting shaft and located above a stop member that separates the

A disposable pipette tip having that is configured to mount on a tip mounting shaft having a locking section and a separate sealing section. The locking section has outwardly extending locking lobes circumferentially spaced around the mounting shaft and located above a stop member that separates the lower sealing section from the upper locking section. The collar flexes out of round when it is mounted over the locking lobes on the mounting shaft. The circumferential shelf on the tip isolates the tip barrel from distortion to enable robust sealing in the barrel below the shelf.

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1. A disposable pipette tip for use with a pipetting system having a tip mounting shaft that includes a lower sealing section and an upper locking section having a stop, two or more outwardly extending lobes located above the stop and spaced circumferentially around the locking section of the mounti

1. A disposable pipette tip for use with a pipetting system having a tip mounting shaft that includes a lower sealing section and an upper locking section having a stop, two or more outwardly extending lobes located above the stop and spaced circumferentially around the locking section of the mounting shaft, and recessed relief portions spanning circumferentially between the lobes and recessed relative to the lobes, each respective lobe having a catch surface that is spaced longitudinally above the stop on the mounting shaft by a predetermined distance, said disposable pipette tip comprising: a barrel having a lower opening through which liquid is aspirated into the barrel and dispensed from the barrel, an upper portion having an inside surface with a circular circumference and an upper end with a circular circumference and an inside diameter, said inside surface of the upper portion of the barrel including a circumferential sealing ring encircling the inside surface of the barrel and extending inward from the inside surface of the barrel;a collar having a continuous inner surface with a circular circumference in its relaxed state, an upper opening for receiving the tip mounting shaft, and a lower end with a circular circumference in its relaxed state and an inside diameter that is larger than the inside diameter of the upper end of the barrel;a circumferential shelf connecting the lower end of the collar to the upper end of the barrel, andmeans on the inner surface of the collar above the circumferential shelf for engaging the catch surfaces on the respective locking lobes after the collar has been distorted outwardly at the lobes and inwardly at the recessed relief portions when the disposable pipette tip is mounted on the tip mounting shaft with the circumferential shelf of the tip engaging the stop on the mounting shaft, said means for engaging being spaced above the circumferential shelf;wherein the collar of the disposable pipette tip is sufficiently flexible to distort outwardly at the lobes on the mounting shaft and inwardly at the recessed relief portions on the mounting shaft between the lobes when the pipette tip is mounted on the tip mounting shaft, and wherein the circumferential shelf has sufficient structural integrity to maintain roundness of the circular circumference of the upper portion of the barrel when the pipette tip is mounted on the tip mounting shaft. 2. A disposable pipette tip as recited in claim 1 wherein the tip mounting shaft further comprises a frustoconical sealing area in the lower sealing section of the shaft, said frustoconical sealing area being located below the stop on the mounting shaft, and further wherein the circumferential sealing ring seals against the frustoconical sealing area or above the frustoconical sealing area when the disposable pipette tip is fully mounted to the mounting shaft. 3. A disposable pipette tip for use with the pipetting system having a tip mounting shaft with a locking section including a stop, 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 and recessed relief portions spanning circumferentially between the lobes and recessed relative to the lobes, each respective lobe having a catch surface that is spaced longitudinally above the stop on the mounting shaft, said disposable pipette tip comprising: a barrel having a lower opening through which liquid is aspirated into the barrel and dispensed from the barrel, an upper portion having an inside surface with a circular circumference and an upper end with a circular circumference and an inside diameter;a collar having a continuous inner surface with a circular circumference in its relaxed state, an upper opening for receiving the tip mounting shaft, and a lower end with a circular circumference in its relaxed state and an inside diameter that is larger than the inside diameter of the upper end of the barrel;a circumferential shelf connecting the lower end of the collar to the upper end of the barrel;a locking ring extending inward from the continuous inner surface of the collar for the entire circumference of the collar except for at least one void in the ring, said locking ring being located above the circumferential shelf at a longitudinal distance along the continuous inner surface of the collar above the circumferential shelf;wherein, when the disposable pipette tip is fully mounted on the tip mounting shaft, the circumferential shelf engages the stop on the tip mounting shaft and the locking ring on the collar engages the respective catch surfaces on the circumferentially spaced outwardly extending lobes on the mounting shaft;and further wherein the collar of the disposable pipette tip is sufficiently flexible to distort outwardly at the lobes on the mounting shaft and inwardly at the recessed relief portions on the mounting shaft between the lobes when the pipette tip is mounted on the tip mounting shaft, and wherein the circumferential shelf has sufficient structural integrity to maintain roundness of the circular circumference of the upper portion of the barrel when the pipette tip is mounted on the tip mounting shaft. 4. A disposable pipette tip as recited in claim 3 wherein the inside surface of the circumferential shelf of the pipette tip extends at a downward angle as it extends from the collar to the barrel. 5. A disposable pipette tip for use with a pipetting system having a tip mounting shaft with a lower sealing section and an upper locking section, the upper locking section including a stop, 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, and recessed relief portions spanning circumferentially between the lobes and recessed relative to the lobes, the lower sealing section of the tip mounting shaft having a diameter less than the diameter of a portion of the upper locking section immediately adjacent the stop and having a circular cross-section, said disposable pipette tip comprising: a barrel having a lower opening through which liquid is aspirated into the barrel and dispensed from the barrel, an upper end with a circular circumference and an inside diameter, and an upper portion having an inside surface with a circular circumference that serves as a sealing area for the tip against the mounting shaft;a collar having a continuous inner surface with a circular circumference in its relaxed state, an upper opening for receiving a tip mounting shaft, and a lower end with a circular circumference it its relaxed state and an inside diameter that is larger than the inside diameter of the upper end of the barrel;a circumferential shelf connecting the lower end of the collar to the upper end of the barrel; andmeans on the inner surface of the collar above the circumferential shelf for engaging the catch surfaces on the respective locking lobes after the collar has been distorted outwardly at the lobes and inwardly at the recessed relief portions when the disposable pipette tip is mounted on the tip mounting shaft with the circumferential shelf of the tip engaging the stop on the mounting shaft, said means for engaging being spaced above the circumferential shelf;means on the upper portion of the barrel below the circumferential shelf for sealing the pipette tip against the lower sealing section of the tip mounting shaft when the disposable pipette tip is mounted on the tip mounting shaft;wherein the collar of the disposable pipette tip is sufficiently flexible to distort outwardly at the lobes on the mounting shaft and inwardly at the recessed relief portions on the mounting shaft between the lobes when the pipette tip is mounted on the tip mounting shaft, and the circumferential shelf has sufficient structural integrity to maintain roundness of the circular circumference of the upper portion of the barrel when the pipette tip is mounted on the tip mounting shaft. 6. A disposable pipette tip as recited in claim 5 wherein said means for sealing the pipette tip against the lower section of the tip mounting shaft comprises a circumferential ring encircling the inside surface of the barrel and extending inward from the inside surface of the barrel; and further wherein, when the disposable pipette tip is fully mounted to the mounting shaft, the circumferential shelf engages the stop on the tip mounting shaft and the collar engages the circumferentially spaced outwardly extending lobes on the mounting shaft above the stop such that the collar distorts outwardly at the lobes and inwardly at the recessed relief portions on the mounting shaft between the lobes, and the circumferential ring at the upper end of the tip barrel seals against the lower sealing section of the tip mounting shaft. 7. A disposable pipette tip as recited in claim 5 wherein the inside surface of the circumferential shelf of the pipette tip extends at a downward angle as it extends from the collar to the barrel. 8. The disposable pipette tip as recited in claim 6 wherein an area of the inside surface of the pipette tip barrel from which the circumferential ring extends has a frustoconical shape. 9. The disposable pipette tip as recited in claim 6 wherein an area of the inside surface of the pipette tip barrel from which the circumferential ring extends has a cylindrical shape. 10. The disposable pipette tip as recited in claim 5 wherein the circumferential shelf reduces the internal bore diameter of the pipette tip by about 0.004 to 0.040 inches. 11. A disposable pipette tip as recited in claim 5 wherein said means for engaging the pipette surfaces on the respective locking lobes comprising a locking ring extending inward from the continuous inner surface of the collar and around the entire circumference of the collar or substantially around the entire circumference of the collar and located at a rim of the upper opening of the collar and above the circumferential shelf at a distance corresponding to the longitudinal distance between the stop on the mounting shaft and a catch surface on the respective locking lobes on the mounting shaft. 12. A disposable pipette tip as recited in claim 11 wherein the locking ring on the pipette tip is substantially, continuously circumferential with a void that provides an opening that vents when the pipette tip is fully mounted on the mounting shaft. 13. A disposable pipette tip as recited in claim 5 wherein said means on the upper portion of the barrel below the circumferential shelf for sealing the pipette tip against the lower sealing section of the tip mounting shaft when the disposable pipette tip is mounted on the tip mounting shaft comprises an upper portion of the inside surface of the barrel adapted to engage an O-ring on the tip mounting shaft, and the disposable pipette tip further comprises a circumferential stabilization ring encircling the inside surface of the barrel and extending inward from the inside surface of the barrel. 14. A disposable pipette tip as recited in claim 6 wherein the tip mounting shaft further comprises a frustoconical sealing area in the lower sealing section, said frustoconical sealing area being located below the stop on the mounting shaft, and the circumferential ring at the upper end of the tip barrel seals against the frustoconical sealing area or above the frustoconical sealing area on the tip mounting shaft.