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Ions for analysis are formed from a liquid sample comprising an analyte in a solvent liquid by directing the liquid sample through a capillary tube having a free end so as to form a first flow comprising a spray of droplets of the liquid sample, to promote vaporization of the solvent liquid. An orif

Ions for analysis are formed from a liquid sample comprising an analyte in a solvent liquid by directing the liquid sample through a capillary tube having a free end so as to form a first flow comprising a spray of droplets of the liquid sample, to promote vaporization of the solvent liquid. An orifice member is spaced from the free-end of the capillary tube and has an orifice therein. An electric field is generated between the free-end of the capillary and the orifice member, thereby causing the droplets to be charged, and the first flow is directed in a first direction along the axis of the capillary tube. Two gas sources, or an arc jet of gas, provide second and third flows, of a gas, and include heaters for heating the second and third flows. The second and third flows intersect with the first flow at a selected mixing region, to promote turbulent mixing of the first, second and third flows, the first, second and third directions being different from one another, and each of the second and third directions being selected to provide each of the second and third flows with a velocity component in the first direction and a velocity component towards the axis of the capillary tube, thereby to promote entrainment of the heated gas in the spray, with the heated gas acting to assist the evaporation of the droplets to release ions therefrom. At least some of the ions produced from the droplets are drawn through the orifice for analysis.

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1. A method of forming ions for analysis from a liquid sample comprising an analyte in a solvent liquid, the method comprising:a) providing a capillary tube having a free end, and an orifice member spaced from the free-end of the capillary tube and having an orifice therein;b) directing the liquid t

1. A method of forming ions for analysis from a liquid sample comprising an analyte in a solvent liquid, the method comprising:a) providing a capillary tube having a free end, and an orifice member spaced from the free-end of the capillary tube and having an orifice therein;b) directing the liquid through the capillary tube and out the free-end, to form a first flow comprising a spray of droplets of the liquid sample, to promote vaporization of the solvent liquid;c) generating an electric field between the free-end of the capillary and the orifice member, and thereby causing the droplets to be charged, and directing the first flow in a first direction along the axis of the capillary tube;d) providing second and third flows of a gas, and heating the second and third flows;e) directing the second and third flows in respective second and third directions to intersect with the first flow at a selected mixing region, to promote turbulent mixing of the first, second and third flows, the first, second and third directions being different from one another, and each of the second and third directions being selected to provide each of the second and third flows with a velocity component in the first direction and a velocity component towards the axis of the capillary tube, thereby to promote entrainment of the heated gas in the spray, with the heated gas acting to assist the evaporation of the droplets to release ions therefrom; andf) drawing at least some of the ions produced from the droplets through the orifice for analysis. 2. A method as claimed in claim 1 which includes providing said selected region spaced from the free end, and directing said first flow away from the orifice. 3. A method as claimed in claim 2, which includes providing said first direction perpendicular to the axis of the orifice. 4. A method as claimed in claim 1, 2 or 3 , wherein the first, second and third directions lie in a common plane. 5. A method as claimed in claim 3, which includes providing the first, second and third directions in a common plane perpendicular to the axis of the orifice. 6. A method as claimed in claim 5, which includes providing the second and third directions symmetrically on either side of a plane including, the axis of the capillary tube and the orifice. 7. A method as claimed in claim 6, which includes providing the second and third directions at an angle of approximately 45 degrees to the first direction. 8. A method as claimed in claim 2, which includes providing at least one additional flow of the gas, heating each of the additional gas flows, and directing each of the additional gas flows toward the selected region at an angle to the first direction, and providing each of the additional gas flows with a velocity component in the first direction and a velocity component toward the axis of the capillary tube. 9. A method of forming ions for analysis from a liquid sample comprising an analyte in a solvent liquid, the method comprising:a) providing a capillary tube having a free end, and an orifice member spaced from the free-end of the capillary tube and having an orifice therein;b) directing the liquid through the capillary tube and out the free-end, to form a first flow comprising a spray of droplets of the liquid sample, to promote vaporization of the solvent liquid;c) generating an electric field between the free-end of the capillary and the orifice member, and thereby causing the droplets to be charged, and directing the first flow in a first direction along the axis of the capillary tube;d) providing a continuous arc jet, of a gas, extending in an arc at least partially around the axis of the capillary tube and heating the arc jet of gas;e) directing the arc jet of gas to intersect with the first flow at a selected mixing region, to promote turbulent mixing of the first flow and the arc jet of gas, all of the arc jet of gas being directed at an angle to the first direction, said angle being selected to provide all of the arc jet of gas with a velocity component in the first direction and a velocity component towards the axis of the capillary tube, thereby to promote entrainment of the heated gas in the spray, with the heated gas acting to assist the evaporation of the droplets to release ions therefrom; andf) drawing at least some of the ions produced from the droplets through the orifice for analysis. 10. A method as claimed in claim 1, 2 , 5 or 9 , which includes providing an exhaust outlet adjacent the selected region and the orifice, and withdrawing spent gas, vaporized liquid and any remaining droplets downstream from the orifice, to reduce unwanted recirculation. 11. A method as claimed in claim 10, which includes providing an outer exhaust tube, connecting the outer exhaust tube to a source of low pressure to draw gas, vaporized liquid and any remaining droplets from the ion source housing and providing an opening between the outer exhaust tube and the exhaust outlet, open to atmosphere, thereby to maintain a pressure not substantially different from atmospheric pressure within the ion source housing. 12. An apparatus for generating ions for analysis from a sample liquid containing an analyte, the apparatus comprising:a) an ion source housing defining an ion source chamber;b) a capillary tube, for receiving the liquid and having a first free end in the chamber for discharging the liquid into the chamber as a first flow comprising a spray of droplets in a first direction;c) an orifice member in the housing and having an orifice therein providing communications between the ion source chamber and the exterior thereof, the orifice being spaced from the free end of the capillary tube;d) connections for the capillary tube and the orifice member, for connection to a power source, to generate an electric field between the free end of the capillary tube and the orifice member; ande) two gas sources, each gas source comprising a heater for the gas and a gas outlet, for generating second and third flows of the gas, wherein the second and third flows are directed in respective second and third directions to intersect with the first flow at a selected mixing region for turbulent mixing of the first, second and third flows, the first, second and third directions being different from one another, and each of the second and third directions providing the second and third flows with a velocity component in the first direction and a velocity component towards the axis of the capillary tube, whereby in use, the spray formed from the first flow turbulently mixes with heated gas of the second and third flows in the selected region, to promote evaporation of droplets of the liquid in the first flow to release ions therefrom and whereby the ions pass through the orifice for analysis. 13. An apparatus as claimed in claim 12, wherein the selected region is spaced from the free end of the capillary and from the orifice. 14. An apparatus as claimed in claim 13, wherein the first direction is perpendicular to the axis of the orifice. 15. An apparatus as claimed in claim 12 or 13 wherein the first, second and third directions lie in a common plane. 16. An apparatus as claimed in claim 14, wherein the first, second and third directions lie in a common plane perpendicular to the axis of the orifice. 17. An apparatus as claimed in claim 16, wherein the second and third directions are located symmetrically on either side of a plane containing the axis of the capillary tube and the orifice. 18. An apparatus as claimed in claim 17, wherein the second and third directions are inclined at an angle of approximately 45 degrees to the first direction. 19. An apparatus as claimed in claim 13, which includes at least one additional gas source. 20. An apparatus as claimed in claim 12, wherein the heater of each of the gas sources comprises a ceramic heater tube including an embedded heater element and heat transfer packaging within the heat tube. 21. An apparatus as claimed in claim 20, wherein the heat transfer packaging comprises ceramic beads. 22. An apparatus as claimed in claim 21, which includes, for each heater, an insulator shell around the ceramic heater tube and spaced therefrom, to form an annular channel for additional gas flows. 23. An apparatus as claimed in claim 22, wherein the annular channel of each heater is filled with ceramic beads to provide additional heat transfer. 24. An apparatus as claimed in claim 23, wherein, for each of the heaters, one end of the insulator shell is closed, an inlet and an outlet for gas are provided at one end of the heater with the inlet opening into the annular channel and with one end of the ceramic heater tube providing the gas outlet. 25. An apparatus for generating ions for analysis from a sample liquid containing an analyte, the apparatus comprising:a) an ion source housing defining an ion source chamber;b) a capillary tube, for receiving the liquid and having a first free end in the chamber for discharging the liquid into the chamber as a first flow comprising a spray of droplets in a first direction;c) an orifice member in the housing and having an orifice therein providing communications between the ion source chamber and the exterior thereof, the orifice being spaced from the free end of the capillary tube;d) connections for the capillary tube and the orifice member, for connection to a power source, to generate an electric field between the free end of the capillary tube and the orifice; ande) a gas source, comprising a heater for the gas and an arc-shaped gas outlet, for generating an arc jet of the gas, wherein the arc jet is directed at an angle to the first direction, to intersect with the first flow at a selected mixing region for turbulent mixing of the first flow and the arc jet of gas, the angle being such as to provide all of the gas of said arc jet with a velocity component in the first direction and a velocity component towards the axis of the capillary tube, whereby in use, the spray formed from the first flow turbulently mixes with heated gas of the arc jet in the selected region, to promote evaporation of droplets of the liquid in the first flow to release ions therefrom and whereby the ions pass through the orifice for analysis. 26. An apparatus as claimed in claim 25, which includes an exhaust opening in the ion source housing, located downstream from the selected mixing region, for withdrawing spent gas and liquid, to reduce recirculation within the ion source housing. 27. An apparatus claimed in claim 26 which includes an outer exhaust tube, a pump connected to the outer exhaust tube for maintaining a sub-atmospheric pressure and an opening between the exhaust opening and the outer exhaust tube, whereby gas and vapour flows from the exhaust outlet and from the opening, through the outer exhaust tube to the pump, balance one another, to maintain a substantially atmospheric pressure within the ion source housing. 28. An apparatus for generating ions from a liquid sample comprising a solvent liquid and an analyte dissolved therein, the apparatus comprising:a) an ion source housing defining an ion source chamber;b) at least one ion source within the ion source housing for generating a spray of droplets of the liquid sample;c) an orifice member in the ion source housing having an orifice therein and being spaced from the ion source;d) connections for connecting the orifice member and the ion source to a power supply for generating an electric field therebetween;e) at least one gas source having a heater and a gas outlet, each gas source being mounted in the ion source housing and being directed in a direction towards a selected mixing region, to promote turbulent mixing of the spray and the gas; andf) a primary exhaust outlet in the ion source housing located adjacent and downstream from the selected region, to reduce recirculation of spent gas and liquid sample within the ion source housing. 29. An apparatus as claimed in clai m 28, which includes a secondary exhaust outlet in the ion source housing, and an internal exhaust guide tube within the housing extending between the primary exhaust outlet and the secondary exhaust outlet. 30. An apparatus as claimed in claim 29, wherein the orifice member has a conical profile, the internal exhaust guide tube is generally circular and is provided with a cut-away portion corresponding to the profile of the orifice member. 31. An apparatus as claimed in claim 29 or 30 which includes an external exhaust outlet tube connected to a pump and extending to the secondary exhaust outlet and an opening between the secondary exhaust outlet and the outer exhaust tube, providing communication to atmosphere whereby a substantial constant atmospheric pressure is maintained in the ion source housing. 32. An apparatus as claimed in claim 31, which includes an intermediate exhaust tube extending from the secondary exhaust outlet, and wherein the opening is annular and is provided between the intermediate and outer exhaust tubes. 33. An atmospheric pressure chemical ionization source comprising:a) a tubular ceramic body defining a substantially tubular flash desorption chamber, opened at one end and closed at the other end;b) a supply tube extending through the closed end of the body to provide at least a spray of a liquid sample containing an analyte dissolved in a solvent liquid; andc) an electrical resistive heating element formed within the ceramic for heating the ceramic to a temperature sufficient to cause flash vaporization of droplets of the liquid sample. 34. An atmospheric pressure chemical ionization source as claimed in claim 33, wherein the ceramic body comprises a first, inner tubular layer, a thin film heater formed on the exterior surface thereof, and an outer cylindrical ceramic layer. 35. An atmospheric pressure chemical ionization source as claimed in claim 33, wherein the supply tube also includes a path for supply of gas for promoting vaporization of solvent liquid. 36. An atmospheric pressure chemical ionization source as claimed in claim 33, 34 , or 35 , wherein the supply tube is removable, and includes a nebulizer probe for insertion into the tubular ceramic body. 37. An atmospheric pressure chemical ionization source as claimed in claim 34, wherein the thin film heater comprises a first portion and a second portion, wherein the first portion is configured to have a higher watt density per unit area to provide a primary flash zone and a second portion, adjacent the open end, having a lower watt density to form a secondary flash zone. 38. A method of forming ions by atmospheric chemical pressure ionization, the method comprising:a) providing a capillary tube with a free end for forming a spray from a liquid sample comprising a solvent liquid and an analyte dissolved therein;b) providing a flow of a gas to promote evaporation of the solvent liquid;c) providing a heated surface around the spray and heating the surface to a temperature sufficient to promote flash vaporization of liquid droplets and prevent substantial contamination of the heater surface by the Leidenfrost effect; andd) providing a corona discharge to ionize free analyte molecules. 39. A method as claimed in claim 38, which includes providing a primary flash zone adjacent the free end of the capillary, providing a first heat flux to the primary flash zone, providing a secondary flash zone downstream from the primary flash zone and providing a second, lower heat flux to the second flash zone.