High sensitivity identification of proteins by electrospray ionization tandem mass spectrometry: initial comparison between an ion trap mass spectrometer and a triple quadrupole mass spectrometer.

Recently, we have shown that a solid-phase-microextraction/capillary electrophoresis device coupled to an electrospray ionization triple quadrupole mass spectrometer through a microelectrospray interface represents a powerful analytical system for the rapid, conclusive and sensitive identification of proteins separated by gel electrophoresis. Here we report on the successful coupling of the same device to an electrospray ionization ion trap mass spectrometer and on the comparative evaluation of the performance of the triple quadrupole and ion-trap-based systems. In the ion trap mass spectrometer-based system, using a tryptic digest of a calibrated bovine serum albumin sample, we achieved limits of detection in the single mass spectrometry (MS) and tandem MS mode, respectively, of 400 amol (if 20 microL of solution at a concentration of 20 amol/microL was applied). The system was also successfully used to identify six yeast proteins isolated from a single analytical two-dimensional polyacrylamide gel. For the detection of unfragmented peptide ions both systems showed comparable sensitivity, whereas the ion-trap-based system showed superior performance with fragment ion spectra.