Aerosol charge adjusting apparatus employing a corona discharge

• US 6,544,484 B1
• Filed: 06/16/2000
• Issued: 04/08/2003
• Est. Priority Date: 06/18/1999
• Status: Expired due to Term

• Current Assignee: TSI Incorporated
• Original Assignee: TSI Incorporated
• Inventors: Kaufman, Stanley L., Dorman, Frank D.
• Primary Examiner(s): Seidleck, James J.
• Assistant Examiner(s): TRAN, THAO T
• Application Number:
  US09/596,159
• Time in Patent Office: 1,026 Days
• Field of Search: 422/186, 422/186.04, 422/186.07
• US Class Current: 422/186.04
• CPC Class Codes: G01N 15/0266 with electrical classification
• CPC Class Codes: G01N 2015/0046 in gas, e.g. smoke
• CPC Class Codes: H01J 49/165 Electrospray ionisation
• CPC Class Codes: H01J 49/168 field ionisation, e.g. corona discharge atmospheric pressure corona discharge per se H01T19/00

Abstract

A system for analyzing aerosols incorporates a corona discharge ion generator with a positively or negatively charged corona discharge needle formed of platinum or a platinum alloy. A high speed (40-210 meter per second) air flow sweeps the ions away from the corona discharge, and propels the ions into a mixing chamber in a turbulent jet that encounters an aerosol, also provided to the mixing chamber. In one version of the ion generator, the ions are carried into the mixing chamber through an orifice formed in a positively or negatively biased plate. In another alternative, the aerosol droplets are electrostatically generated, and propelled into the mixing chamber as an aerosol jet that confronts the ion jet to enhance a mixing of the charged droplets and the ions. In this version the droplets are advantageously neutralized to leave predominantly singly charged positive and negative particles, to provide a neutralized aerosol particularly well suited for analysis with a mass spectrometer.

Claims

1. A system for generating a charge-adjusted aerosol, including:

an enclosure defining a mixing chamber, a first orifice for admitting an aerosol into the chamber, and a second orifice for admitting corona discharge ions into the chamber;

an electrostatic droplet generator having an electrostatic discharge region adapted to generate multiple electrically charged droplets of a sample including an electrically conductive liquid and a non-volatile material dispersed substantially uniformly throughout the liquid;

a first ion generator having a first corona discharge region electrically biased to generate multiple first ions;

a first fluid passage adapted for a coupling with a gas source to guide a first gas flow past the electrostatic discharge region to entrain at least a portion of the charged droplets and form an aerosol of the sample, and to carry the entrained droplets into the mixing chamber through the first orifice to direct an aerosol jet into the mixing chamber; and

a second fluid passage adapted for a coupling with a gas source to guide a second gas flow past the corona discharge region to entrain at least a portion of the first ions and carry the entrained ions into the mixing chamber through the second orifice to direct a first ion carrying jet into the mixing chamber;

wherein the aerosol jet and the first ion carrying jet merge inside the mixing chamber in a turbulent flow that promotes a mixing of the charged droplets and the first ions, to alter the droplet charges toward a neutralizing of the aerosol; and

wherein the enclosure further defines an exit orifice permitting the aerosol to exit the mixing chamber after said altering of the droplet charges.

2. The system of claim 1 wherein:

the electrically charged droplets, during said altering, also are reduced in size by evaporation of the liquid.

3. The system of claim 2 wherein:

the evaporation is substantially complete while the aerosol is inside the mixing chamber, whereby the aerosol exits the chamber as a stream of particles consisting essentially of the non-volatile material.

4. The system of claim 2 wherein:

the charged droplets are monodisperse, and said altering proceeds at a rate sufficient to prevent the charged droplets from disintegrating due to repulsive Coulombic forces as they evaporate, whereby the aerosol remains substantially monodisperse as it exits the enclosure.

5. The system of claim 1 further including:

an aerosol characterizing device disposed to receive the aerosol from the enclosure.

6. The system of claim 5 wherein:

the aerosol characterizing device is selected from the group of devices consisting of;

a differential mobility analyzer in combination with either a condensation nucleus counter or an electrometer; and

a mass spectrometer.

7. The system of claim 1 wherein:

the enclosure includes an electrically conductive plate, the second orifice is formed through the plate, and the plate and the corona discharge region are electrically biased to the same electrical polarity.

8. The system of claim 7 wherein:

the electrically conductive plate and the corona discharge region are negatively biased.

9. The system of claim 1 wherein:

the aerosol jet and the ion carrying jet are oppositely directed.

10. The system of claim 1 wherein:

the first ion carrying jet travels past the corona discharge region at a mean velocity of at least about 40 meters per second, and the corona discharge region is spaced apart from the second orifice by a distance of less than one millimeter.

11. The system of claim 10 wherein:

the aerosol jet is directed into the neutralization chamber at a mean velocity through the first orifice of at least about 40 meters per second.

12. The system of claim 1 wherein:

the first ion generator includes an electrically conductive needle providing the corona discharge region, mounted within an electrically conductive ion generator housing and electrically biased with respect to said housing.

13. The system of claim 12 wherein:

the needle, at least along the corona discharge region, is formed of a noble metal.

14. The system of claim 1 wherein:

the droplet generator includes a capillary having a first end submerged in the liquid sample and a second end region comprising the electrostatic discharge region and mounted within an electrically conductive droplet generator housing; and

the liquid sample at the electrostatic discharge region is electrically biased with respect to the housing.

15. The system of claim 14 wherein:

the first gas flow includes air, and further includes an electronegative gas selected from the group consisting of carbon dioxide and sulfur hexafluoride and provided at a flow rate off at least about three percent of the first gas flow.

16. The system of claim 1 further including:

a second ion generator having a second corona discharge region disposed proximate the enclosure and biased to an electrical polarity opposite that of the first corona discharge region, thereby to generate multiple second ions and oppositely charged with respect to the first ions;

a third fluid passage adapted for a coupling with a gas source to guide a third gas flow past the second corona discharge region to entrain at least a portion of the second ions and carry the entrained ions into the mixing chamber through a third orifice to direct a second ion carrying jet into the chamber;

wherein the second ion carrying jet is oriented to merge with the first ion carrying jet and the aerosol jet in said turbulent flow.

17. The system of claim 16 wherein:

the first and second ion carrying jets are oppositely directed, and the aerosol jet is substantially perpendicular to the ion jets.

18. A device for adjusting the electrical charge distribution of an aerosol, including:

an enclosure defining a chamber, a first orifice to permit an aerosol to flow into the chamber from outside of the enclosure, and a second orifice permitting entry of ions into the chamber;

a first ion generator electrically biased to generate multiple first ions at at a first corona discharge region thereof disposed proximate the second orifice;

a first fluid passage adapted for a coupling with a gas source to guide a first gas flow past the first corona discharge region to entrain at least a portion of the first ions having a selected electrical polarity and to carry the entrained ions into the chamber through the second orifice, to merge with an aerosol flowing into the chamber through the first orifice, thus to alter an electrical charge distribution of the aerosol; and

a conductive member proximate the second orifice, forming part of the enclosure and electrically isolated from a remainder of the enclosure whereby the conductive member is adapted to be electrically biased relative to said remainder of the enclosure;

wherein the enclosure further defines an exit orifice to allow the aerosol to exit the enclosure after the electrical charge distribution is altered.

19. The device of claim 18 wherein:

the conductive member comprises a conductive plate electrically biased to have said selected electrical polarity, and the second orifice is formed through the conductive plate.

20. The device of claim 18 further including:

a second ion generator having a second corona discharge region electrically biased to a polarity opposite to that of the first ion generator to generate multiple second ions charged oppositely from the first ions; and

a second fluid passage adopted for a coupling to a gas source to guide a second gas flow past the second corona discharge region to entrain at least a portion of the second ions and carry the entrained ions into the chamber through a third orifice.

21. The device of claim 18 wherein:

the first gas flow and the entrained first ions travel through the second orifice into the chamber at a mean velocity of at least about 40 meters per second.

22. The device of claim 18 further including:

a switching means for selectively changing the polarity of the electrical bias applied to the corona discharge region.

23. The device of claim 18 further including:

a droplet generator adapted to generate multiple droplets of a liquid sample that includes a non-volatile material substantially uniformly dispersed throughout the liquid, the droplet generator having an electrostatic discharge region at which the droplets are generated; and

a second fluid passage adapted for a coupling to a gas source to guide a second gas flow past the electrostatic discharge region to entrain at least a portion of the droplets to provide said aerosol as an aerosol of the liquid sample, and to carry the entrained droplets into the chamber through the first orifice to merge with the first gas flow including the entrained first ions.

24. The device of claim 23 wherein:

the aerosol, and the first gas flow including the entrained first ions, are provided through the first and second orifices, respectively, at mean velocities sufficient to provide respective aerosol and ion carrying jets, whereby the merger of the jets promotes a mixing of the droplets and the first ions to enhance the efficiency at which the electrical charge distribution of the aerosol is altered.

25. The device of claim 18 wherein:

the first ion generator includes an electrically conductive discharge needle mounted within and electrically isolated from an electrically conductive ion generator housing, and electrically biased with respect to the housing.

26. The device of claim 25 wherein:

the discharge needle, at least along the corona discharge region, is formed of a noble metal.

27. An electrospray-ionization mass spectrometry system, including:

an enclosure defining a mixing chamber, a first orifice for admitting an aerosol to the chamber, a second orifice for admitting corona discharge ions into the chamber, and an exit orifice for permitting the neutralized aerosol to exit the enclosure;

an electrostatic droplet generator having an electrostatic discharge region adapted to generate multiple electrically charged droplets of a liquid sample that includes a liquid and a non-volatile material dispersed substantially uniformly throughout the liquid;

an ion generator having a corona discharge region electrically biased to generate multiple ions at the corona discharge region;

a first fluid passage adapted for a coupling with a gas source to guide a first gas flow past the electrostatic discharge region to entrain at least a portion of the charged droplets and form an aerosol of the sample, and to carry the entrained droplets into the mixing chamber through the first orifice;

a second fluid passage adapted for a coupling with a gas source to guide a second gas flow past the corona discharge region to entrain at least a portion of the ions and carry the entrained ions into the mixing chamber through the second orifice, to merge with the aerosol to mix the charged droplets and the ions and thereby alter the droplet charges toward a neutralizing of the aerosol; and

a mass spectrometer disposed to receive the aerosol after it exits the enclosure.

28. The device of claim 27 wherein:

the electrically charged droplets, during the altering of the droplet charges, also are reduced in size due to evaporation of the liquid.

29. The device of claim 28 wherein:

the evaporation is substantially completed while the aerosol is inside the mixing chamber, whereby the aerosol exits the chamber as a stream of particles consisting substantially of the non-volatile material.

30. The system of claim 28 wherein:

the charged droplets are monodisperse, and the charge altering proceeds at a rate sufficient to prevent the charged droplets from disintegrating due to repulsive Coulombic forces as they evaporate, whereby the aerosol remains monodisperse as it exits the enclosure.

31. The device of claim 27 wherein:

the enclosure includes an electrically conductive plate, the second orifice is formed through the plate, and the plate and the corona discharge region are electrically biased and have the same electrical polarity.

32. A corona discharge device for altering an electrical charge distribution of an aerosol, including:

an enclosure defining a chamber, a first orifice to permit an aerosol to flow into the chamber, a second orifice to permit corona discharge ions to enter the chamber, and an exit orifice;

an ion generator including an electrically conduction corona discharge needle having a corona discharge region disposed proximate the second orifice and electrically biased to generate multiple ions, wherein the discharge needle at least along the corona discharge region is formed of a noble metal; and

a fluid passage adapted for a fluid coupling a gas source to guide as gas flow past the corona discharge region to entrain at least a portion of the ions and to carry the entrained ions into the chamber through the second orifice at a mean velocity of at least about 40 meters per second, to encounter and merge with an aerosol flowing into the chamber through the first orifice, thus to alter an electrical charge distribution of the aerosol.

33. The device of claim 32 wherein:

the noble metal is selected from the group consisting of;

platinum, an alloy including platinum and iridium, and gold.

34. The device of claim 32 further including:

an electrically conductive member proximate the corona discharge region and the second orifice electrically biased and having the same electrical polarity as the corona discharge region.

35. The device of claim 32 further including:

a switching means for selectively changing the electrical polarity of the bias applied to the corona discharge needle.