Mass Spectroscopy

In MALDI-TOF mass spectrometry, protein or peptide samples are mixed with a matrix compound (usually an aromatic organic acid that donates a proton to the analyte) and dried onto a metal sample plate. After the plate is placed in a high vacuum source chamber in the mass spectrometer, a small portion of the sample is vaporized (desorption) by blasts from a nitrogen laser. The ions produced 'fly' up a tube to the mass analyzer and their masses (actually their mass-to-charge ratio) are determined by their 'time-of-flight'. The range of measurements using MALDI is in excess of 100 kDa although accuracy falls off at this size. The lower practical limits are several hundred daltons as there is considerable interference in this range of the spectra from matrix and other low mass contaminants.

The LCQ DecaXP uses electrospray as an ionization source. Samples may be infused into the instrument using a syringe or applied directly into the instrument from an in-line HPLC system that separates peptides using reversed phase chromatography. Sample preparation is much more critical for this method than for MALDI-TOF mass spectrometry. It is very sensitive to sample media. Therefore, samples for infusion should be prepared in water, if possible, or in acetonitrile or methanol. Although tolerated at very low levels, trifluoroacetic acid is discouraged as an ion-pairing agent. Formic acid is suggested in its place. Please contact us for further information concerning sample preparation, amount and concentration electrospray mass spectrometry.