![]() Thus the analyte molecules are irregularly distributed, and the center of the spot is frequently empty or covered with fine small crystals. In aqueous solutions, most of the small crystals of the matrix generally begin to grow at the margin of the wet area on the metal plate and continue to grow toward the center of the wet area. ![]() In general, the wetted area is not uniformly coated. For example, when a drop of sample and matrix solution that is placed onto a clean metal sample support plate dries on a metal surface, the sample spot consisting of small matrix crystals spreads over the formerly wet area. As a result, analysis time for each sample increases, as the laser may need to search until it finds the target analyte that is sufficient for analysis. As the sample dries, the target analyte randomly concentrates in localized regions. Because the MALDI laser focuses on only a small percentage of the total area of the applied sample, only a small fraction of the applied diluted sample will be vaporized and detected, resulting in decreased sensitivity.Īn additional problem with spotting a sample onto a traditional MALDI plate pertains to the drying of the sample on the plate. In addition, samples typically become diluted during the sample preparation step because of the relatively large elution volumes that are required. These additional steps may lead to significant sample loss and potential re-contamination of the sample. However, all of these products require several manipulation steps prior to application of the sample onto the MALDI plate. Several commercially available products are available for this application. The adsorbed analytes are subsequently eluted from the sorbent with an appropriate solvent. ![]() For example, a mixture of analytes is passed through a packed bed containing such sorbents, and the analytes adsorb to the packing material, while the salts are not retained. One existing method for salt removal utilizes reversed-phase sorbents such as C18-silica or divinylbenzene-based polymers. In particular, salts can dramatically affect the quality of the resulting mass spectra due to adduct formation. Many of the issues associated with sample preparation for MALDI mass spectrometry are summarized in Bruker's UK patent application (GB 2332273A). It is well known that the sensitivity of the analysis and the speed of automation are highly dependent on preparation and purity of the sample on the MALDI plate. Mass spectrometry (MS) with ionization by matrix-assisted laser desorption and ionization (MALDI) has become a useful tool for the analysis of large molecules, e.g., biopolymers, such as proteins, peptides, oligonucleotides, DNA, RNA, etc. The entire contents of the aforementioned patent applications are incorporated herein by this reference.BACKGROUND OF THE INVENTION PCT/US02/16501 filed May 24, 2002, designating the United States, and published in English as international publication WO 02/096541 A1 on Dec. §371, of PCT international application Ser. national phase application, pursuant to 35 U.S.C.
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