Sample Preparation and Purity
Mass analyzers are very sensitive and can measure femtomole amounts of purified material although the quality of the signal is directly related to the concentration and purity of the sample provided. MALDI is relatively less sensitive to the presence of contaminants such as salts or denaturants than other mass spectrometric methods (i.e. electrospray ionization). However, certain reagents are deleterious to sample analysis. This is particularly true of detergents and other non-volatile substances such as glycerol and dimethyl sulfoxide. If detergents are absolutely required we recommend using n-octylglucoside as it does not interfere as much with the analysis as others.
Sodium dodecyl sulfate is particularly deleterious as are the non-ionic detergents Triton and Tween and must be avoided.
Electrospray is far more sensitive to contaminating substances and greater care must be exercised in sample preparation for this method (please see comments above). Avoid salts, detergents and other non-volatile substances. We prefer that the samples be submitted in water or acetonitrile or methanol, if possible. Please call to discuss your individual needs.
Amount of Sample needed for Analysis
For routine mass analysis of single proteins up to 10 kDa, we require 10 l of 1 micromolar (1
µM) solution. Analysis of larger proteins (up to 80 kDa) requires proportionately more material and request that you supply 5-10 l of a 10 M solution. In all cases, the complexity of the sample must be considered and relatively more material supplied as the sample becomes more complex (i.e. more than one component).
In general, peak heights in MALDI spectra are not quantitative and do not accurately represent the relative abundance of the peptides or proteins in the mixture.
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