Method for microdispensing of fluids from a pipette

• US 20030213905A1
• Filed: 05/16/2002
• Published: 11/20/2003
• Est. Priority Date: 05/16/2002
• Status: Active Grant

• Current Assignee: Thermo Finnigan LLC (Thermo Fisher Scientific Incorporated)
• Original Assignee: Large Scale Proteomics Corporation
• Inventors: Lennon, John, Norouzi, Taraneh
• Granted Patent: US 6,734,424 B2
• Time in Patent Office: Days
• US Class Current: 250/288
• CPC Class Codes: B01L 13/02 for receptacle or instruments
• CPC Class Codes: B01L 2200/142 Preventing evaporation
• CPC Class Codes: B01L 2400/022 droplet contacts the surface of the receptacle
• CPC Class Codes: B01L 2400/0487 fluid pressure, pneumatics
• CPC Class Codes: B01L 3/0262 using touch-off at substrate or container
• CPC Class Codes: G01N 2035/102 Preventing or detecting loss of fluid by dripping
• CPC Class Codes: G01N 35/1004 Cleaning sample transfer devices
• CPC Class Codes: G01N 35/1016 Control of the volume dispensed or introduced
• CPC Class Codes: H01J 49/00 Particle spectrometers or separator tubes

Abstract

An automated pipetting apparatus and method for forming sample spots on a support include a pipette. A robotic assembly moves a sample container, such as a multiwell microtiter plate, and the support to the pipette for receiving and dispensing liquid samples. The pipette draws a predetermined volume of the liquid sample from the sample container into the axial passage of the pipette and forms a pocket of a gaseous material above and forms a barrier material below the volume of the liquid sample. The liquid sample is drawn into the pipette a distance sufficient to form a space between the liquid sample and the outlet of the pipette and to contain the liquid sample completely within the pipette. The volume of the barrier material, which is typically air or other fluid, separates the liquid sample a suitable distance from the outlet end of the pipette to prevent the liquid sample from flowing outward under gravity and being drawn along the outer surfaces of the pipette by the surface tension of the liquid, thereby preventing or inhibiting evaporation and preventing deposits from forming on the outer surface of the pipette. The pipette dispenses the liquid sample with sufficient force so that substantially the entire volume of the liquid sample is dispensed from the pipette directly onto the support. The support can be, for example, a sample plate of a MALDI mass spectrometer. The pipette deposits the liquid samples to form sample spots on the sample plate for analysis by the mass spectrometer.

Claims

1. A method of depositing a liquid sample onto a support, said method comprising the steps of:

drawing a volume of a liquid sample through an open axial end of a pipette into an axial passage of said pipette;

drawing a volume of a barrier material through said open axial end of said pipette to draw said volume of said liquid sample into said axial passage and to space said volume of liquid sample from said axial end by said volume of said barrier material, where said liquid sample is spaced from said axial end of said pipette a distance to inhibit evaporation of said liquid sample; and

positioning said open axial end of said pipette above a target site of said support, expelling said volume of said barrier material from said pipette, and discharging said liquid sample onto said target-site.

2. The method of claim 1, wherein said barrier material is a gas.

3. The method of claim 1, wherein said barrier material is selected from the group consisting of liquids, emulsions, slurries, powders and foams.

4. The method of claim 1, wherein said barrier material is a liquid, emulsion, slurry or foam and said method comprises drawing said volume of liquid sample into said pipette to form an air space and thereafter drawing said barrier material into said pipette.

5. The method of claim 1, comprising depositing a plurality of said liquid samples on said support to form a microarray of sample spots.

6. The method of claim 1, comprising drawing said volume of liquid sample into said axial passage of said pipette a distance from said open axial end to inhibit evaporation of said liquid sample from said pipette.

7. The method of claim 6, comprising drawing said volume of liquid sample into said axial passage a distance to prevent said liquid sample from wicking from said axial passage to an outer surface of said pipette.

8. The method of claim 2, wherein said gas is air.

9. The method of claim 1, comprising drawing said volume of said barrier material into said pipette a distance to substantially prevent leakage and evaporation of said liquid sample from said pipette.

10. The method of claim 2, comprising

positioning said open axial end of said pipette into a vessel containing said liquid sample,

applying a suction to said pipette to draw said volume of liquid sample into said axial passage, and thereafter withdrawing said open axial end from said vessel and drawing said volume of gas into said pipette, and

discontinuing said suction to retain said volume of liquid sample in said pipette.

11. The method of claim 1, wherein said pipette contains a pressure transmitting liquid for drawing and dispensing said liquid sample from said pipette.

12. The method of claim 1, wherein said liquid sample contains a volatile solvent or carrier.

13. The method of claim 1, wherein said liquid sample has a vapor pressure of at least about 3.5 kPa at 25°

C.

14. The method of claim 1, wherein said volume of said barrier material is an amount sufficient to inhibit evaporation of said liquid sample from said pipette.

15. The method of claim 1, wherein said volume of said liquid sample is about 2 ml or less.

16. The method of claim 1, wherein said volume of said liquid sample is about 10 microliters or less.

17. The method of claim 1, comprising providing a plurality of said pipettes and simultaneously drawing a volume of said liquid samples into said pipettes followed by drawing a volume of said barrier material, and discharging said samples onto said support to form a microarray of sample spots.

18. A method of loading a liquid material onto a mass spectrometer plate, said method comprising the steps of:

drawing a volume of a liquid material into a pipette and drawing a volume of a barrier material into said pipette to space said volume of said liquid sample from an outlet end of said pipette to inhibit loss of said liquid material from said pipette;

positioning said pipette in a dispensing location with respect to a mass spectrometer plate while retaining said volume of said liquid sample completely within said pipette; and

discharging said barrier material and at least a portion of said volume of said liquid sample from said pipette and depositing said liquid sample onto a target site on said plate.

19. The method of claim 18, wherein said barrier material is air and said method comprises discharging said volume of said liquid sample completely from said pipette.

20. The method of claim 18, wherein said liquid material is a volatile liquid, and said method comprises drawing said volume of said barrier material into said pipette to space said volume of said liquid sample from said outlet end of said pipette a distance to inhibit evaporation of said liquid sample from said pipette.

21. The method of claim 20, comprising drawing said volume of said barrier material into said pipette to space said volume of said liquid sample from said outlet end of said pipette to inhibit wicking of said liquid sample onto an outer surface of said pipette.

22. The method of claim 18, wherein said liquid sample contains a solvent or carrier that is volatile at room temperature and atmospheric pressure.

23. The method of claim 19, comprising

positioning said outlet end of said pipette in a vessel containing said liquid sample,

applying a suction to said pipette to draw said volume of said liquid sample into said pipette and withdrawing said pipette from said liquid sample in said vessel while continuing said suction to draw said volume of air into said pipette, and

thereafter discontinuing said suction and retaining said volume of liquid in said pipette.

24. The method of claim 18, wherein said pipette contains a pressure transmitting liquid for drawing said liquid sample into said pipette and discharging said liquid sample from said pipette.

25. The method of claim 18, wherein said volume of liquid sample is about 0.5 microliters to about 1.5 microliters.

26. The method of claim 25, wherein said volume of said barrier material is about 0.5 microliters to about 1.5 microliters.

27. The method of claim 18, comprising the step of applying a dispensing pressure to said pipette to discharge said liquid sample from said pipette.

28. The method of claim 18, wherein said liquid sample has a vapor pressure of at least about 3.5 kPa at 25°

C.

29. The method of claim 18, wherein said pipette is a micropipette and said volume of said liquid material is about 10 microliters or less.

30. The method of claim 18, wherein said mass spectrometer plate is a MALDI mass spectrometer plate.

31. The method of claim 18, wherein said barrier material is selected from the group consisting of liquids, emulsions, slurries, powders and foams, and wherein said method comprises drawing said liquid material into said pipette a distance to form an air space between said liquid material and thereafter drawing said barrier material into said pipette.

32. The method of claim 18, wherein said barrier material is mineral oil.

33. A method of loading a sample onto a mass spectrometer plate, said method comprising the steps of:

inserting an open axial end of a pipette into a liquid sample supply, said pipette having an axial passage in communication with said open axial end;

drawing a volume of said liquid sample into said axial passage;

removing said open axial end of said pipette from said liquid sample supply and drawing a volume of a barrier material into said pipette through said open axial end to space said volume of said liquid sample from said open axial end of said pipette a distance to inhibit evaporation of said liquid sample from said pipette and to prevent wicking of said liquid sample onto an outer surface of said pipette caused by surface tension; and

positioning said open axial end of said pipette over a target site on a mass spectrometer plate and discharging said barrier material and said volume of said liquid sample from said pipette to load said volume of said liquid sample on said target site on said mass spectrometer plate.

34. The method of claim 33, wherein said barrier material is air and said method comprises the step of applying a suction to said pipette to draw said volume of liquid and said volume of air into said pipette.

35. The method of claim 33, comprising applying a dispensing pressure to said pipette to discharge said liquid sample from said pipette.

36. The method of claim 34, comprising maintaining said suction while removing said open end of said pipette from said liquid sample to draw said volume of air into said pipette and thereafter discontinuing said suction.

37. The method of claim 33, wherein said liquid sample contains a volatile liquid and has a vapor pressure of greater than about 3.5 kPa at 25°

C.

38. The method of claim 33, wherein said pipette contains a pressure transmitting liquid for drawing and dispensing said liquid sample.

39. The method of claim 38, comprising applying a suction to draw said pressure transmitting liquid into said pipette and to draw an air space into said pipette before drawing said liquid sample.

40. The method of claim 33, wherein said barrier material is a liquid having a vapor pressure less than a vapor pressure of said liquid sample.

41. The method of claim 33, wherein said barrier material is air and is drawn into said pipette to form said air pocket having a volume sufficient to inhibit evaporation of said liquid sample from said pipette.

42. A method of forming a sample spot on a mass spectrometer plate suitable for mass spectrometer analysis, comprising the steps of:

loading a liquid sample containing an analyte to be analyzed onto a support plate to form a liquid sample spot;

pipetting a liquid matrix material directly onto said liquid sample spot, said liquid containing a volatile liquid having a vapor pressure of at least about 3.5 kPa at 25°

C.; and

evaporating said volatile liquid to form a matrix material containing said analyte.

43. The method of claim 42, wherein said liquid sample spot contains a mass spectrometry matrix material.

44. The method of claim 42, wherein said volatile liquid contains a mass spectrometry matrix material.

45. The method of claim 42, comprising drawing said liquid matrix forming material into a pipette to define a volume of said liquid matrix forming material and spacing said volume from an outlet end of said pipette by a barrier material having a volume to inhibit evaporation of said liquid matrix forming material from said pipette.

46. The method of claim 45, wherein said barrier material is air.

47. The method of claim 45, wherein said barrier material is selected from the group consisting of liquids, emulsions, slurries, powders and foams.

48. The method of claim 45, wherein said volume of said liquid matrix forming material is spaced from said outlet end of said pipette a distance to inhibit wicking of said volatile liquid from said pipette on an outer surface of said pipette.

49. The method of claim 42, comprising forming a pocket of a gaseous material in said pipette on an upstream side of said volume of said liquid matrix forming material.

50. The method of claim 49, comprising applying a dispensing pressure to said pipette to dispense said volume of said liquid matrix forming material onto said sample spot with sufficient force to inhibit droplets of said liquid matrix forming material from adhering to said pipette.