MALDI-TOF is tolerant of potentially interfering solutes, but keep salt concentrations to less than 50 mM and avoid glycerol, detergents and urea. Solubility may be sample dependent. Try water first, then add acetonitrile, and then add 0.1% TFA to increase solubility. For samples submitted in solution, 5 uL of a 10 pmol/uL solution will be sufficient to obtain data.

MALDI-TOF mass spectrometry of proteins can present problems that are sample specific. They may require optimization of matrix, sample dilution and internal standard calibration. For these reasons, it is not advised that protein samples are submitted prespotted.

The preferred matrices are:

• 2,5 dihydroxybenzoic acid (2,5 DHB) for peptides < 4000 Da
• a-cyano-4-hydroxycinnamic acid (aCHCA) for peptides < 8000 Da
• sinapinic acid for proteins > 8000 Da
• 3-hydroxypicolinic acid/L-tartartic acid diammonium salt(5:1) for oligos

Samples are mixed with saturated organic matrix, applied to the target plate and dried. Up to 100 samples can be spotted on the target plate. If a prespotted plate is submitted, 5 spots should be left open for external calibration standards. If high accuracy is required the sample should include an internal calibrant. If you are unsure of the amount of your sample, apply several serial dilutions and make a note of this on the requisition form. We will examine all dilutions, but will collect data and bill you only for the one giving the best spectrum.