Method of and apparatus for ionizing an analyte and ion source probe for use therewith

A method of forming ions for analysis from a liquid sample comprising an analyte in a solvent liquid, the method comprising the steps of:

• 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;
• f) drawing at least some of the ions produced from the droplets through the orifice for analysis.

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;
• 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;
• and
• e) two gas sources, each gas source comprising a heater for the gas and a gas outlet, for generating second and third flows, of gas, wherein the second and third flows are directed 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.

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;
• 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;
• e) a gas source, comprising a heater for the gas and an arc-shaped gas outlet, for generating an arc jet, of 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.

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 selection mixing region, to promote turbulent mixing of the spray and the gas;
• f) 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.

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;
• and
• c) 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.

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;
• d) providing a corona discharge to ionize free analyte molecules.