Introduction of ions into mass spectrometers through laval nozzles
View Patent ↗Ions entrained in a gas are transported into the vacuum system of an ion user, such as a mass spectrometer, from an ion source located outside the vacuum. The gas and ions pass through a nozzle that connects the ion source to the vacuum system and is shaped to form a supersonic gas jet in a first vacuum chamber of the vacuum system. In the first vacuum chamber, ions entrained in the supersonic gas jet are extracted electrically or magnetically and are collected, for example, by an RF ion funnel and transmitted to the ion user. The supersonic gas jet travels on and, after passing through the first vacuum chamber, the supersonic gas jet is directed into a separate pump chamber out of which the gas is pumped.
1. A method for the transfer of ions contained in a gas from a first region containing gas having a first pressure into a second region containing gas having a second pressure lower than the first pressure, comprising
(a) accelerating the gas with the ions between the first and the second regions by a nozzle to form a supersonic gas jet;
(b) extracting ions from the supersonic gas jet in the second region in a direction substantially perpendicular to an axis of propagation of the supersonic gas jet by using electric or magnetic fields and;
(c) directing the supersonic gas jet devoid of the extracted ions through the second region into a separate pump chamber in which the gas of the supersonic gas jet is pumped off; and
(d) transferring the extracted ions to an ion analyzer for analyzing the extracted ions.
2. The method of claim 1 , wherein the nozzle is a Laval nozzle.
3. The method of claim 1 , further comprising collecting ions of extracted from the gas jet in the second region by an RF ion funnel and transmitting the collected ions of interest as an ion beam.
4. The method of claim 3 , wherein parameters of the ion funnel are adjusted so that a desolvation of the collected ions occurs due to collisions of the ions with gas molecules.
5. The method of claim 4 , wherein pressure and temperature parameters of the gas in the RF ion funnel are adjusted so that a desolvation of the collected ions occurs.
6. The method of claim 4 , wherein an RF voltage is applied to the RF ion funnel and a frequency and amplitude of the RF voltage are adjusted so that a desolvation occurs.
7. The method of claim 1 , wherein the ions in the gas in the first region form an ion cloud and the method further comprises guiding the ions from the ion cloud to the nozzle by one of gas flow and ion migration in an electric potential distribution.
8. An ion spectrometer, comprising:
a device for the generation of ions in a gas in a region containing gas at a first pressure;
a chamber containing gas at a second pressure that is lower than the first pressure;
a nozzle connecting the region to the chamber, which nozzle is shaped so that a supersonic gas jet is generated by gas and ions passing through the nozzle from the region into the chamber, the supersonic gas jet passing through the chamber;
an extraction structure that extracts ions from the supersonic gas jet in the chamber in a direction substantially perpendicular to an axis of propagation of the supersonic gas jet, collects the extracted ions and guides the collected ions to an ion analyzer; and
a pump chamber located adjacent to the chamber, into which the supersonic gas jet devoid of the extracted ions enters through an aperture, and from which the gas of the supersonic gas jet is pumped off.
9. The ion spectrometer of claim 8 , wherein the nozzle has a shape of a Laval nozzle.
10. The ion spectrometer of claim 8 , wherein the extraction structure comprises an ion funnel located in the chamber that collects ions extracted from the supersonic jet and transmits the collected ions to the ion analyzer.
11. The ion spectrometer of claim 8 , comprising one of an elongated reaction tube and a gas feeder funnel located in the region and connected with a gas-tight connection to the nozzle.
12. The ion spectrometer of claim 8 , wherein the ion analyzer is one of a mass spectrometer and an ion mobility spectrometer.