Resolution improvement in the coupling of planar differential mobility analyzers with mass spectrometers or other analyzers and detectors

• US 20080251714A1
• Filed: 04/11/2007
• Published: 10/16/2008
• Est. Priority Date: 04/10/2006
• Status: Active Grant

• Current Assignee: Sociedad Europea de Analisis Diferencial de Movilidad SL
• Original Assignee: Sociedad Europea de Analisis Diferencial de Movilidad SL
• Inventors: de la Mora, Juan Fernandez, Juan, Rus-Perez
• Granted Patent: US 7,928,374 B2
• Time in Patent Office: Days
• US Class Current: 250/288
• CPC Class Codes: G01N 27/623 combined with mass spectrometry
• CPC Class Codes: H01J 49/004 Combinations of spectrometers, tandem spectrometers, e.g. MS/MS, MSn

Abstract

Prior work on differential mobility analysis (DMA) combined with mass spectrometry (MS) has shown how to couple the output of the DMA with the inlet of an atmospheric pressure ionization mass spectrometer (APCI-MS). However, the conventional ion inlet to an APCI-MS is a round orifice, while conventional DMA geometries make use of elongated slits. The coupling of two systems with such different symmetries limits considerably the resolutions attainable by the DMA in a DMA-MS combination below the value of the DMA alone. The purpose of this invention is to overcome this limitation in the case of a parallel plate DMA. One solution involves use of an elongated rather than a circular MS sampling hole, with the long dimension of the MS inlet hole aligned with that of the DMA slit. Another involves use of a more elongated orifice in the DMA exit and a more circular hole on the MS inlet, the two being connected either through a short transfer conduit or through an ion guide. The DMAs described can also be coupled profitably to detectors and analyzers other than mass spectrometers.

Claims

1. ) A method to transmit mobility-selected ions from the ion exhaust of a DMA with approximately planar symmetry into the inlet orifice of a MS with approximately cylindrical symmetry, where either said ion exhaust of said DMA, or said inlet orifice of said MS are non-circular.

2. ) A method according to claim 1 where said ion exhaust and said inlet orifice have approximately the same elongated cross sections.

3. ) A method according to claim 1 where said mobility-selected ions exiting said ion exhaust of said DMA with approximately planar symmetry are transmitted to said inlet orifice of said MS by a transfer line, while one end of said transfer line connects with said ion exhaust and the other end connects with said inlet orifice, where said ion exhaust is more elongated that said inlet orifice.

4. ) A method according to claim 1 where said mobility-selected ions exiting said ion exhaust of said DMA with approximately planar symmetry are transmitted by an ion guide to said inlet orifice of said MS.

5. ) A method according to claim 1 where two interior surfaces of said DMA with approximately planar symmetry are formed by two conducting electrodes closing two opposite open areas of an electrically insulating box-shaped structure.

6. ) A method according to claim 5 where sheath gas flow enters said DMA through a laminarization screen pressing directly against said two conducting electrodes, such that said interior surfaces of said electrodes located downstream from said screen do not offer discontinuities of materials to the flow that could lead to steps and precipitate transition to turbulence.

7. ) An approximately planar DMA apparatus to separate ions according to their electrical mobility, two of whose wetted surfaces are conducting electrodes closing tightly two opposite open surfaces of an insulating box-shaped structure.

8. ) An apparatus according to claim 7 where sheath gas flow enters said DMA through a laminarization screen pressing directly against said two conducting electrodes, such that said surfaces of said electrodes located downstream from said screen do not offer discontinuities of materials to the flow that could lead to steps and precipitate transition to turbulence.

9. ) An apparatus according to claim 8 reduced to practice according to FIGS. 67 and 8

10. ) An apparatus according to claim 7 operated in tandem with a mass spectrometer accepting ions carried in a gas at pressures higher than 1 torr.

11. ) An apparatus according to claim 10 where said ions carried in a gas enter into the mass spectrometer through a noncircular orifice.

12. ) A mass spectrometer accepting ions carried in a gas at pressures higher than 1 torr, where said ions carried in said gas enter into said mass spectrometer through a non-circular orifice.