Figure 4

A profile (a) and centroid (b) version of the same spectrum. The profile raw data detected by a mass spectrometer consists of distributed signal across m/z values at each point where an ion is detected. Centroid data is raw data that has been processed by an algorithm to retain only the local maximum in each range in which an ion is detected. Because each ion detected creates an m/z distribution of signal, the distribution itself (in profile mode) or the maximum to which it is reduced (its centroid) is sometimes called a peak. This ion intensity distribution along m/z is not to be confused with the distribution of ion intensity along time in chromatographic studies (see Figure 2).