Resolution improvement in the coupling of planar differential mobility analyzers with mass spectrometers or other analyzers and detectors
First Claim
1. A method of transmitting gas carrying mobility-selected ions from the ion exhaust of a DMA with approximately planar symmetry into an inlet orifice of an analytical instrument, the method including:
- providing a DMA with approximately planar symmetry and a non-circular exhaust;
arranging said non-circular exhaust such that a gas carrying mobility-selected ions emitted from said non-circular exhaust is directed towards an inlet orifice of an analytical instrument; and
operating said DMA to cause a gas carrying mobility-selected ions to emit from said non -circular exhaust towards said inlet orifice of said analytical instrument.
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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.
15 Citations
15 Claims
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1. A method of transmitting gas carrying mobility-selected ions from the ion exhaust of a DMA with approximately planar symmetry into an inlet orifice of an analytical instrument, the method including:
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providing a DMA with approximately planar symmetry and a non-circular exhaust; arranging said non-circular exhaust such that a gas carrying mobility-selected ions emitted from said non-circular exhaust is directed towards an inlet orifice of an analytical instrument; and operating said DMA to cause a gas carrying mobility-selected ions to emit from said non -circular exhaust towards said inlet orifice of said analytical instrument. - View Dependent Claims (2, 3, 4, 5, 6, 14, 15)
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7. An approximately planar DMA apparatus to separate ions according to their electrical mobility, comprising:
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i) a box-shaped insulating structure with several wide openings, including an open top surface and an open bottom surface; ii) a top conducting electrode closing said top open surface, and a bottom conducting electrode closing said bottom open surface; and iii) a first sealing gasket placed between said top conducting electrode and said top open surface, and a second sealing gasket placed between said bottom conducting electrode and said bottom open surface, such that substantial leakage of gas through the union of said insulating box and said conducting electrodes is avoided. - View Dependent Claims (8, 9, 10, 11)
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- 12. An approximately planar DMA including a shaped ion outlet conduit, said conduit having an entry section more elongated than its exit section, where the cross sectional area of said more elongated entry section is larger than the cross sectional area of said exit section, such that the flow does not become sonic within said more elongated entry section.
Specification