Discontinuous atmospheric pressure interface
A method of interfacing atmospheric pressure ion sources, including electrospray and desorption electrospray ionization sources, to mass spectrometers, for example miniature mass spectrometers, in which the ionized sample is discontinuously introduced into the mass spectrometer. Discontinuous introduction improves the match between the pumping capacity of the instrument and the volume of atmospheric pressure gas that contains the ionized sample. The reduced duty cycle of sample introduction is offset by operation of the mass spectrometer under higher performance conditions and by ion accumulation at atmospheric pressure.
1. A method for analyzing a sample, the method comprising:
discontinuously receiving sample ions to a mass analyzer of a mass spectrometer in a manner in which the mass analyzer is periodically open for a period of time that causes the pressure in the mass analyzer to increase above a pressure at which mass analysis or ion manipulation can be conducted and is periodically closed while the mass analyzer is evacuated to a pressure at which mass analysis or ion manipulation can be conducted; and
performing mass analysis on the sample ions while the mass analyzer is at a pressure at which mass analysis or ion manipulation can be conducted.
2. The method according to claim 1 , wherein the method further comprises generating the sample ions using an ionizing source.
3. The method according to claim 2 , wherein the ionizing source operates by a technique selected from the group consisting of: electrospray ionization, nano-electrospray ionization, atmospheric pressure matrix-assisted laser desorption ionization, atmospheric pressure chemical ionization, desorption electrospray ionization, atmospheric pressure dielectric barrier discharge ionization, atmospheric pressure low temperature plasma desorption ionization, laser-assisted electrospray ionization, and electrospray-assisted laser desorption ionization.
4. The method according to claim 1 , wherein the mass analysis is a tandem mass analysis.
5. The method according to claim 4 , wherein the tandem mass analysis is performed without addition of collision gas.
6. The method according to claim 1 , wherein discontinuously receiving comprises:
opening a valve of a discontinuous interface, wherein opening of the valve allows for ions to pass through the discontinuous interface to the mass analyzer of the mass spectrometer; and
closing the valve.
7. The method according to claim 6 , wherein a computer synchronizes the opening and the closing of the valve with operation of ion optics of the mass spectrometer.
8. The method according to claim 1 , wherein the mass spectrometer is a miniature mass spectrometer.
9. The method according to claim 1 , wherein the mass analyzer comprises a linear ion trap.
10. The method according to claim 1 , wherein the sample is a biological sample.
11. An analysis system, the system comprising:
an ionization source;
a discontinuous interface operably associated with the ionization source;
a mass analyzer operably associated with the discontinuous interface; and
a computer operably connected to the system, wherein the computer contains a processor configured to execute a computer readable program that causes the system to:
open a channel of the discontinuous interface;
apply low RF voltage in the mass analyzer to trap ions in the mass analyzer, the mass analyzer being above a pressure at which mass analysis or ion manipulation can be conducted;
close the channel of the discontinuous interface;
evacuate the mass analyzer to a pressure at which mass analysis or ion manipulation can be conducted; and
conduct tandem mass analysis of the ions in the mass analyzer.
12. The system according to claim 11 , wherein the discontinuous interface comprises a valve.
13. The system according to claim 12 , wherein the program controls the position of the valve in order to open and close the channel of the discontinuous interface.
14. The system according to claim 11 , wherein the ionization source is a dielectric barrier discharge ionization source.
15. The system according to claim 11 , wherein the mass analyzer is part of a miniature mass spectrometer.
16. The system according to claim 15 , further comprising a diaphragm pump operably associated with the mass analyzer.
17. The system according to claim 16 , wherein the diaphragm pump is operable at 5 L/min.
18. The system according to claim 11 , wherein the mass analyzer comprises a linear ion trap.