Method and apparatus for maldi analysis
First Claim
1. An improved method for matrix assisted laser desorption/ionization (MALDI) of an analyte material, such method comprising the steps of preparing a specimen comprised of a major portion of matrix material and a minor portion of analyte material, wherein said matrix and analyte are deposited as a sample on a support illuminating said matrix such that material including the analyte is desorbed from a surface of the sample and ionized, and initially confining said desorbed material such that desorption momentum is at least partially directionally randomized by collisional interaction thereby conditioning the desorbed analyte to control its initial conditions for analysis.
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Abstract
Matrix assisted laser desorption/ionization is performed in a manner to thermalize large analyte ions in a plume of desorbed material for spectroscopic analysis. The thermalized ions have a low or zero mean velocity and are presented at a well-defined instant in time, reducing artifacts and sharpening the spectral peaks. In one embodiment the light is delivered to a matrix or sample holder having a cover, baffle or compartment. The baffle or compartment impedes or contains a plume of desorbed material and the analyte undergoes collisions to lower its mean velocity and directionality. Thus “thermalized” the analyte ions are passed to a mass analysis instrument. In a preferred embodiment an optical fiber butts up against a thin transparent plate on which the specimen resides, with the matrix side in a vacuum acceleration chamber. A mechanical stage moves the specimen in both the x- and y- directions to select a point on the specimen which is to receive the radiation. The use of a fiber optic illuminator allows the entire stage assembly to be subsumed essentially within the dimensions of a conventional stage. In other embodiments, a thermalizing compartment is provided in a capillary tube about the end of the illumination fiber and the sample matrix is deposited along the inner cylindrical wall of the tube, so the capillary forms a migration path to the outlet for thermalization of the desorbed analyte. In other embodiments microstructures having the shape of a small lean-to, overhang or perforated cover plate, or providing a high aspect surface texture, provide the necessary containment to promote thermalization of the released analyte. A thin layer or cover of fibrous or permeable material may also be used to thermalize the analyte before mass analysis, and in other embodiment this material may also act as the substrate. An automated instrument may include a fixed array of illumination fibers which are illuminated at different times to eject samples from a corresponding array of points on the specimen.
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Citations
22 Claims
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1. An improved method for matrix assisted laser desorption/ionization (MALDI) of an analyte material, such method comprising the steps of
preparing a specimen comprised of a major portion of matrix material and a minor portion of analyte material, wherein said matrix and analyte are deposited as a sample on a support illuminating said matrix such that material including the analyte is desorbed from a surface of the sample and ionized, and initially confining said desorbed material such that desorption momentum is at least partially directionally randomized by collisional interaction thereby conditioning the desorbed analyte to control its initial conditions for analysis.
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13. A method of sampling a matrix assisted laser desorbed ionized material comprising the steps of
illuminating a matrix to desorb material, and passing said material through a permeable barrier effective to at least partially thermalize the desorbed material thereby controlling initial conditions for analysis of said material.
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14. Apparatus for providing an ionized sample of material to an analysis instrument such as a mass spectrometer or the like, the apparatus comprising
a stage for holding a specimen from which said sample is to be provided means directed at the stage for illuminating the specimen to cause desorption of material from the sample and ionization thereof, whereby the desorbed material has a directional momentum, and means for confining said desorbed material sufficiently to at least partially thermalize said directional momentum so that large molecules in said material are reduced in velocity,said means for confining having an outlet communicating with the analysis instrument to provide the large molecules of reduced velocity thereto.
- 20. Apparatus for matrix assisted laser desorption of a large molecule analyte, such apparatus comprising a support stage including means for holding a sample on a substrate in a defined region of the stage an optical fiber having a first end adapted to couple to a light source for receiving a light input, and a second end held by said stage in a position to illuminate a spot region on the sample, the stage positioning the second end so that its output beam passes through the substrate to directly illuminate said spot region on the sample with a spot of defined size at a fluence effective to desorb the analyte from the sample, whereby the desorbed material has a directional momentum and the apparatus further comprises a means for confining said desorbed material sufficiently to at least partially thermalize said directional momentum.
Specification