A mass spectrometer and a method of mass spectrometry are disclosed wherein periodic background noise is effectively filtered out from the mass spectral data. An overall mass window is superimposed upon the mass spectral data. The overall mass window preferably comprises 21 nominal mass windows each preferably having a width of 1.0005 amu. Each nominal mass window preferably comprises 20 channels. An intensity distribution relating to all the first channels of the 21 nominal mass windows is determined. An intensity quantile is determined from the intensity distribution. The intensity quantile is taken to represent the background intensity in the first channel of the central nominal mass window. This process is repeated for the other channels so that the background intensity across the whole of the central nominal mass window is estimated and then subtracted from the raw mass spectral data comprising the central nominal mass window. The overall mass window is then preferably advanced approximately 1 amu and the process is repeated multiple times.
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority from UK patent application no. GB 0329544.0 filed 22 Dec. 2003 and U.S. patent application No. 60/585,772 filed 7 Jul. 2004. The contents of these applications are incorporated herein by reference.
