Controlled kinetic energy ion source for miniature ion trap and related spectroscopy system and method
An ion trap mass spectrometry system adapted for portability and related method includes an ion source for generating ions from a sample to be analyzed, and a resistive drift tube coupled to an output of the ion source for receiving the ions injected therein. The resistive drift tube decelerates the ions to provide cooled ions having a mean translational kinetic energy of less than 5 keV. A miniature ion trap or trap array, such having apertures <1 mm, is coupled to an output of the resistive drift tube for trapping the cooled ions. A spectrometer is coupled to the miniature ion trap for analyzing the cooled ions.
1. An ion trap mass spectrometry system, comprising:
an ion source for generating ions from a sample to be analyzed;
a resistive drift tube coupled to an output of said ion source for receiving said ions, said drift tube having a voltage applied along its length, wherein a resulting electric field decelerates said ions to provide cooled ions having a mean translational kinetic energy of less than 5 keV, and wherein an inner surface layer of said resistive drift tube comprises a semi-conductor devoid of both electrodes and electrically insulating materials and being operable to reduce distortions in said electric field within said drift tube by transferring surface charge away from said inner surface of said drift tube, said semi-conducting layer having a resistance between 10 5 and 10 11 ohms, wherein an inner diameter of said resistive drift tube is <0.5 cm;
a miniature ion trap coupled to an output of said resistive drift tube for trapping said cooled ions, wherein said miniature ion trap provides apertures <5 mm; and
a time-of-flight spectrometer coupled to said miniature ion trap for analyzing said cooled ions, wherein said system applies a direct current, end-to-end voltage difference of 20V/cm or less across said resistive drift tube.
2. The system of claim 1 , wherein said miniature ion trap provides apertures <1 mm.
3. The system of claim 1 , wherein said system applies a direct current, end-to-end voltage difference of 2V/cm or less across said resistive drift tube.
4. The system of claim 1 , wherein said inner diameter is <0.1 cm.
5. The system of claim 1 , wherein said ion source is an electrospray, laser ablation, MALDI, field emitting array, or an electron impact (EI) ionization source.
6. A method of controlling translational ion kinetic energy, comprising the steps of:
providing a resistive drift tube, having an inner diameter <0.5 cm, coupled to an ion trap or ion trap array, said drift tube having an electric field applied along its length, and wherein an inner surface layer of said resistive drift tube comprises a semi-conductor and is devoid of both electrodes and electrically insulating materials and being operable to reduce distortions in said electric field within said drift tube by transferring surface charge away from said inner surface of said drift tube;
injecting ions generated by an ion source spaced apart from said resistive drift tube into said resistive drift tube, wherein said ions are decelerated by said applied field while in said resistive drift tube to provide cooled ions having mean translational kinetic energies less than 5 keV;
applying a direct current, end-to-end voltage difference of 20V/cm or less across said resistive drift tube during said injecting ions generated by an ion source step; and
injecting said cooled ions into said ion trap or ion trap array, wherein said ion trap or ion trap array provides apertures <5 mm.
7. The method of claim 6 , further comprising the step of controlling said average translational kinetic energy using a pressure in said resistive drift tube and said applied field in said resistive drift tube.
8. The method of claim 6 , further comprising the step of injecting said cooled ions in said ion trap or ion trap array into a spectrometer.
9. The method of claim 8 , wherein said spectrometer is a time-of-flight mass spectrometer or an ion mobility spectrometer.
10. The method of claim 6 , wherein said ion source is an electrospray, laser ablation, MALDI, field emitting array, or an electron impact (EI) ionization source.
11. The method of claim 6 , further comprising providing the semiconducting layer with a resistance between 10 5 and 10 11 ohms.
12. The method of claim 6 , further comprising operating said resistive drift tube at a pressure of between 0.01 mTorr and atmospheric pressure.
13. The method of claim 6 , wherein the semi-conducting layer comprises a doped lead silicate glass.
14. The system of claim 1 , wherein the semi-conducting layer comprises a doped lead silicate glass.
15. The method of claim 6 , further comprising:
applying a direct current, end-to-end voltage difference of 2V/cm or less across said resistive drift tube during said injecting ions generated by an ion source step.
16. The method of claim 6 , further comprising:
operating said resistive drift tube at a pressure less than 1 Torr.