Appendix 5.1 Methods of Sample Preparation for Analysis by MALDI

1 Appendix 5.1 Methods of Sample Preparation for Analysis by MALDI 

Overlayer (also Two Layer and Seed Layer) Method this method (several variants have been developed by different research groups) is a combination of the crushed crystal and fast evaporation methods. Fast solvent evaporation is used to form the first layer of small matrix-only crystals, followed by deposition of a solution of matrix plus analyte on top of the crystal layer. The difference between the fast evaporation and the overlayer methods is in the second layer solution, where the addition of matrix to the latter is believed to provide improved results particularly for mixtures. The method has several convenient features that make it a popular approach. It inherits all the advantages of the fast evaporation method and avoids some of its limitations, while providing enhanced sensitivity and better spot-to-spot reproducibility. 

Sandwich method this method is derived from the fast evaporation and overlayer methods. The sample analyte is not premixed with matrix instead a sample droplet is applied on top of a fast evaporated matrix-only bed as in the fast evaporation method, followed by deposition of a second layer of matrix in a nonvolatile solvent so that the sample is sandwiched between the two matrix layers. This method is not widely used. 

Quick and Dirty this aptly named sample preparation technique is widely used to obtain fast results without consideration of signal optimization. It is simple, fast and broadly applicable, and completely decouples matrix handling from sample handling with little or no sample purification prior to analysis. Typically, a one microlitre 

Most early efforts focused on the development of thin layer matrix precoated membranes, including those made of nylon and other synthetic polymers, nitrocellulose, anion- and cation-modified cellulose and regenerated cellulose. Several manufacturers currently offer 96-well plates with proprietary coatings for LC-MALDI-MS applications. This approach was described in more detail above. As mentioned previously, all of these sample preparation methods were originally developed for pre-purified samples or fractions, not for analytes eluting from an HPLC or capillary electrophoresis column. 

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