The ThermoScientific Exactive Orbitrap 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.
Typically, peptides below 2000 daltons are amenable to this technique. Proteins above 2000 daltons can be analyzed but with reduced success due to our lack of adequated deconvolution software. Proteins must be exquisitely free of salts, detergents and other contaminants to have any chance of success by this approach. MALDI-TOF mass spec is better suited to larger proteins.