The sample preparation for mass spectrometry is used for the optimisation of a sample for the analysis in a mass spectrometer (MS). These have depending on their ion source different requirements for volume, concentration, and composition of the analyte solution. Furthermore, in protein mass spectrometry usually the protein of interest is cleaved into peptides before analysis, either by in-gel digestion or by proteolysis in solution.

Matrix-assisted laser desorption/ionization

For matrix-assisted laser desorption/ionization (MALDI) mass spectrometry the sample is usually mixed with a matrix solution and spotted on the target plate. The matrix crystallises together with the sample and the analyte molecules are transferred to the gas phase by the pulsed laser irradiation.

The concentration of salt in the sample is thereby not so critical as it is for electrospray ionization. However, interfering signals are observed due to side reactions of the matrix with alkali metal ions which can impair the analysis of the spectra. Nevertheless, a separate desalting step is usually not necessary as in previous steps of sample preparation e.g. in-gel digestion of proteins, the selection of appropriate buffer salts prevents the occurrence of this problem. Furthermore the crystallised matrix/analyte mixture allows removing of salts by washing on the target and the addition of ammonium phosphate before crystallisation can improve the signal quality.

In analytical chemistry, sample preparation refers to the ways in which a sample is treated prior to its analysis. Preparation is a very important step in most analytical techniques, because the techniques are often not responsive to the analyte in its in-situ form, or the results are distorted by interfering species. Sample preparation may involve dissolution, reaction with some chemical species, pulverizing, treatment with a chelating agent (e.g. EDTA), masking, filtering, dilution, sub-sampling or many other techniques.

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