Evaporative electrical detector

• US 6,568,245 B2
• Filed: 03/13/2002
• Issued: 05/27/2003
• Est. Priority Date: 03/15/2001
• Status: Active Grant

• Current Assignee: TSI Incorporated
• Original Assignee: TSI Incorporated
• Inventors: Kaufman, Stanley L.
• Primary Examiner(s): Raevis, Robert R.
• Assistant Examiner(s): Cygan, Michael
• Application Number:
  US10/098,936
• Publication Number:
  US 20020132362A1
• Time in Patent Office: 440 Days
• Field of Search: 73/280.1, 73/280.2, 73/615.8, 73/615.9, 73/616.1, 738/655, 73/617.1, 324/464, 324/465, 95/69, 95/72, 95/79, 96/17
• US Class Current: 73/28.02
• CPC Class Codes: G01N 2030/8452 Generation of electrically charged aerosols or ions
• CPC Class Codes: G01N 2030/847 by pneumatic means
• CPC Class Codes: G01N 2030/8482 by electrical or glow discharge
• CPC Class Codes: G01N 30/64 Electrical detectors
• CPC Class Codes: G01N 30/84 Preparation of the fraction to be distributed
• CPC Class Codes: Y10T 436/25125 Digestion or removing interfering materials
• CPC Class Codes: Y10T 436/25375 Liberation or purification of sample or separation of material from a sample [e.g., filtering, centrifuging, etc.]

Abstract

An aerosol detector, particularly well suited for liquid chromatography applications, includes a corona discharge source controlled to selectively charge the non-volatile residue particles of an aerosol. The aerosol initially is composed of droplets of a liquid sample, with the residue particles resulting from droplet evaporation. The selectively charged residue particles, each carrying a charge in proportion to its size, are collected at a conductive filter. The electrical current along a conductor coupled to the filter is measured repeatedly or continuously to provide an indication of concentrations of the non-volatile material. Preferably, a pneumatic nebulizer is used to generate the aerosol. When used in a liquid chromatography system, the detector can yield several separated areas of relatively high electrical current, corresponding to concentrations of several different analytes in the liquid sample.

Claims

1. A process for measuring concentrations of non-volatile constituents in liquids, including:

providing a sample including a liquid and at least one non-volatile constituent contained in the liquid to a separator adapted to separate the different non-volatile constituents from one another by concentrating different non-volatile constituents primarily into different regions within the sample;

receiving at least a portion of the sample exiting the separator, and using said portion to generate an aerosol stream composed of droplets including the liquid and the at least one non-volatile constituent;

allowing the liquid to substantially evaporate, whereby the aerosol stream after evaporation is composed of residue particles of the at least one non-volatile constituent;

after allowing the liquid to substantially evaporate, applying an electrical charge to each of the residue particles dependent on the residue particle'"'"'s size;

generating an electrical signal having a level proportional to an aggregate electrical charge of a selected sequence of the electrically charged residue particles in the aerosol stream; and

using the electrical signal to indicate a concentration of the at least one non-volatile constituent in the liquid sample over a region thereof corresponding to the selected sequence of the charged residue particles.

2. The process of claim 1 wherein:

the separator comprises a liquid chromatography column adapted to cause different non-volatile constituents to travel through the column at respective different rates as the sample progresses through the column, whereby the different regions of the sample exit the column at different times;

providing a sample includes intermittently injecting the sample into a carrier liquid stream to form plugs of the sample that travel with the carrier liquid; and

moving the sample through a separator comprises moving the carrier liquid and the plugs through the separator.

3. The process of claim 2 wherein:

the liquid sample includes at least two different non-volatile constituents;

the selected sequence of the electrically charged residue particles encompasses at least first and second different regions of the liquid sample corresponding to concentrations of first and second kinds of the non-volatile constituents respectively; and

said using the electrical signal comprises indicating first and second concentrations corresponding to the first and second regions respectively.

4. The process of claim 1 wherein:

generating the electrical signal in proportion to the aggregate electrical charge comprises using an electrically conductive component to collect the charged residue particles of the selected sequence, and sensing an electrical current along an electrical conductor coupled to the collector component.

5. The process of claim 4 wherein:

sensing the electrical current includes continuously measuring the electrical current to provide a continuous record of the electrical current versus time over a time span corresponding to the selected sequence.

6. The process of claim 1 wherein:

said applying an electrical charge to each of the residue particles comprises generating multiple ions, and using a gas stream to entrain and carry at least a portion of the ions into a confluence with the aerosol stream.

7. The process of claim 6 further including:

accelerating the aerosol stream and the gas stream proximate said confluence of the gas stream with the aerosol stream.

8. A process for determining non-volatile residue concentrations, including:

generating an aerosol stream composed of liquid droplets containing non-volatile material;

drying the droplets, whereby the aerosol stream at a point downstream of aerosol stream generation is composed of residue particles of the non-volatile material;

generating multiple ions, and providing a gas flow past the ions to entrain at least a portion of the ions in the gas flow to provide an ion stream;

after drying the droplets, directing the ion stream and the aerosol stream towards one another and into a turbulent merger to promote a mixing of the ions and the residue particles to apply a size-dependent electrical charge to each of the residue particles;

generating an electrical signal having a level proportional to an aggregate electrical charge of a selected sequence of the electrically charged residue particles in the aerosol stream; and

using the electrical signal to indicate a concentration of the at least one non-volatile material in the liquid sample over a region thereof corresponding to the selected sequence of the charged residue particles.

10. The process of claim 8 further including:

accelerating the aerosol stream and the ion stream proximate said turbulent merger.

11. The process of claim 8 wherein:

generating the electrical signal in proportion to the aggregate electrical charge comprises using an electrically conductive component to collect the charged residue particles of the selected sequence, and sensing an electrical current along an electrical conductor coupled to the conductive component.

12. The process of claim 11 wherein:

sensing the electrical current includes continuously measuring the electrical current to provide a continuous record of the electrical current versus time over a time span corresponding to the selected sequence.

13. The process of claim 8 wherein:

said applying an electrical charge to each of the residue particles comprises generating multiple ions, and using a gas stream to entrain and carry at least a portion of the ions into a confluence with the aerosol stream.

9. The process of wherein:

said generating the electrical signal includes generating the electrical signal at a level proportional to said concentration to the “

Xth”

power, wherein;

14. A system for analyzing liquid samples containing non-volatile analytes, including:

an analyte separator adapted to separate different non-volatile analytes in a liquid sample by concentrating the different non-volatile analytes primarily into different regions within the liquid sample;

a nebulizer disposed to receive the liquid sample from the separator, and adapted to nebulize at least a portion of the liquid sample to generate an aerosol stream composed of droplets of the liquid sample suspended in a carrier gas and containing the at least one analyte, the droplets tending to evaporate whereby the aerosol stream at a selected location downstream of the nebulizer is composed of residue particles of the at least one analyte;

an electrical charger disposed to receive the aerosol stream near the selected location and adapted to apply a size-dependent electrical charge to each of the residue particles; and

a charge-responsive device disposed to receive the electrically charged residue particles and adapted to generate an electrical signal in proportion to an aggregate charge of the received residue particles and thereby indicate a concentration of the at least one analyte in the liquid over a range determined by the received residue particles.

15. The system of claim 14 wherein:

the analyte separator comprises a liquid chromatography column adapted to cause the different non-volatile analytes in the liquid sample to travel therethrough at different rates as the liquid sample flows through the column, whereby the different regions exit the column at different times.

16. The system of claim 15 further including:

a pump for providing the liquid sample to the liquid chromatography column under an elevated pressure.

17. The system of claim 15 further including:

a first liquid supply for providing a carrier liquid stream to the liquid chromatography column at a substantially constant flow rate, and a second liquid supply operable to introduce predetermined amounts of the liquid sample by injection into the carrier liquid stream.

18. The system of claim 14 wherein:

the liquid sample contains first and second different analytes substantially concentrated within respective first and second regions of the liquid sample as the liquid sample exits the liquid chromatography column; and

the received residue particles include first and second temporally separated portions corresponding to the first and second regions respectively, whereby the electrical signal indicates first and second concentrations of the first and second analytes, respectively.

19. The system of claim 14 wherein:

the charge-responsive device comprises a collector for accumulating the residue particles.

20. The system of claim 19 wherein:

the collector comprises an electrically conductive filter adapted to entrap the residue particles;

the charge-responsive device further includes a conductor electrically coupled to the filter and a measuring circuit coupled to the conductor for sensing an electrical current along the conductor; and

the electrical signal consists essentially of the electrical current.

21. The system of claim 20 wherein:

the measuring circuit is adapted to continually measure the electrical current to provide a continuous record of the electrical current versus time over at least one selected time span corresponding to a selected sequence of the received residue particles.

22. The system of claim 14 wherein:

the charge-responsive device includes an analog-to-digital converter adapted to convert the electrical signal to a digital value.

23. The system of claim 22 further including:

a digital processor coupled to the analog to digital converter for computing the concentration of the at least one analyte based on the digital value.

24. The system of claim 14 wherein:

the charge-responsive device comprises an electrometer.

25. The system of claim 14 wherein:

the nebulizer is selected from the group consisting of;

pneumatic nebulizers, ultrasonic nebulizers, thermospray nebulizers, and electrostatic nebulizers.

26. The system of claim 14 wherein:

the electrical charger comprises an ion generator.

27. The system of claim 26 wherein:

the ion generator comprises an electrically conductive member adapted to provide a corona discharge.

28. The system of claim 14 wherein:

the electrical charger provides a unipolar charge.

29. The system of claim 14 further including:

a diffusion dryer disposed between the nebulizer and the electrical charger to facilitate evaporation of the liquid droplets as the aerosol stream proceeds toward the electrical charger.

30. The system of claim 14 wherein:

said charge-responsive device is configured to generate the electrical signal at a level proportional to said concentration to the “

Xth”

power, wherein;

31. A detector for determining concentrations of non-volatile analytes in liquid solutions, including:

a nebulizer disposed to receive a liquid incorporating non-volatile material, and adapted to nebulize at least a portion of the liquid to generate an aerosol stream composed of droplets of the liquid suspended in a carrier gas, the droplets tending to evaporate whereby the aerosol stream at a selected location downstream of the nebulizer is composed of residual particles of the non-volatile material suspended in the carrier gas;

an ion generator disposed near the selected location;

a source of compressed gas for providing a gas flow, and a fluid conduit adapted to guide the gas flow past the ion generator to entrain at least a portion of the ions and carry the entrained ions into a confluence with the aerosol stream, to apply a size-dependent electrical charge to each of the residue particles; and

a charge-responsive device disposed to receive the charged residue particles and adapted to generate an electrical signal having a level proportional to an aggregate charge of the received residue particles, thereby to indicate a concentration of the non-volatile material in the liquid.

32. The detector of claim 31 wherein:

the fluid conduit is shaped to accelerate the gas flow proximate the aerosol stream, to promote a turbulent mixing of the ions and the residue particles.

33. The detector of claim 32 wherein:

the charge-responsive device comprises a collector for accumulating the residue particles.

34. The detector of claim 33 wherein:

the collector comprises an electrically conductive filter adapted to entrap the non-volatile residue particles;

the charge-responsive device further includes a conductor electrically coupled to the filter and a measuring circuit coupled to the conductor for sensing an electrical current along the conductor; and

the electrical signal consists essentially of the electrical current.

35. The detector of claim 34 wherein:

the measuring circuit is adapted to continuously measure the electrical current level to provide a continuous record of the electrical current versus time over at least one selected time span corresponding to a selected sequence of the received residue particles.

36. The detector of claim 31 wherein:

the charge-responsive device comprises an electrometer.

37. The detector of claim 31 wherein:

the charge-responsive device includes an analog-to-digital converter adapted to convert the electrical signal to a digital value.

38. The detector of claim 37 further including:

a digital processor coupled to the analog to digital converter for computing the concentration of the at least one analyte based on the digital value.

39. The detector of claim 31 wherein:

the nebulizer is selected from the group consisting of;

pneumatic nebulizers and electrostatic nebulizers.

40. The detector of claim 31 wherein:

the ion generator comprises an electrically conductive member adapted to provide a corona discharge.

41. The detector of claim 31 wherein:

the electrical charger provides a unipolar charge.

42. The detector of claim 31 further including:

a diffusion dryer disposed between the nebulizer and the electrical charger to facilitate evaporation of the liquid droplets as the aerosol stream proceeds toward the electrical charger.

43. The detector of claim 31 wherein:

said charge-responsive device is configured to generate the electrical signal at a level proportional to said concentration to the “

Xth”

power, wherein;

55. The device of claim 43 further including:

a diffusion dryer disposed along the first fluid passage to facilitate evaporation of the liquid droplets as the aerosol stream proceeds toward the chamber.

56. The device of claim 43 wherein:

said charge-responsive device is configured to generate the electrical signal at a level proportional to said concentration to the “

Xth”

power, wherein;

44. The detector of further including:

a means for accelerating the aerosol stream proximate said confluence to further promote said turbulent mixing.

45. A non-volatile analyte concentration detection device including:

an enclosure defining a chamber;

a first fluid passage disposed to receive an aerosol stream composed of liquid droplets containing non-volatile material and suspended in a carrier gas, said first fluid passage being adapted to guide the aerosol stream toward the chamber as the liquid droplets substantially evaporate whereby the aerosol stream as it enters the chamber is composed of residue particles of the non-volatile material;

an ion generator disposed near the chamber and adapted to generate multiple ions;

a second fluid passage for guiding a gas flow toward the chamber and past the ion generator, to entrain at least a portion of the ions and carry the entrained ions into the chamber to merge with the aerosol stream, thus to apply a size-dependent electrical charge to each of the residue particles; and

a charge-responsive device disposed downstream of an exit of the chamber to receive at least a portion of the charged residue particles and adapted to generate an electrical signal having a level proportional to an aggregate charge of the received residue particles, thereby to indicate a concentration of the non-volatile material.

46. The device of claim 45 wherein:

the first and second fluid passages include respective first and second flow restrictions near the chamber to accelerate the aerosol stream and the ion-carrying gas flow, respectively, as they enter the chamber.

47. The device of claim 45 wherein:

the charge-responsive device comprises a collector for accumulating the residue particles.

48. The device of claim 47 wherein:

the collector comprises an electrically conductive filter adapted to entrap the residue particles;

the charge-responsive device further includes a conductor electrically coupled to the filter, and a measuring circuit coupled to the conductor for sensing a level of electrical current along the conductor; and

the electrical signal consists essentially of the electrical current.

49. The device of claim 48 wherein:

the measuring circuit is adapted to continuously measure the electrical current to provide a continuous record of electrical current versus time over at least one selected time span corresponding to a selected sequence of the received residue particles.

50. The device of claim 48 further including:

an analog-to-digital converter adapted to convert the electrical current to a digital value.

51. The device of claim 50 further including:

a digital processor coupled to the analog to digital converter for computing the concentration of the at least one analyte based on the digital value.

52. The device of claim 45 wherein:

the charge-responsive device comprises an electrometer.

53. The device of claim 45 wherein:

the ion generator comprises an electrically conductive member adapted to provide a corona discharge.

54. The device of claim 45 wherein:

the electrical charger provides a unipolar charge.