Total ion count, TIC

Figure 8.4 Typical total ion count (TIC) of a bitumen extract from the exterior surface of an archaeological shard obtained by GC-MS. IS = internal standard (C34 w-alkane). This is identical to the output of a GC.

Typical total ion count (TIC) of a bitumen extract from... 

Normalization is a very important step, as it aims to reduce experimental variance. Normalization is most often performed by dividing each spectrum by a normalization factor (Figure 2G). The most popular normalization factor is calculated as the total ion count (TIC), which is the sum of all ion intensities in a spectrum. Several studies discovered that in MSI the assumptions for TIC applicability hold true only for very homogeneous tissues. In heterogeneous samples, more robust normalization factors based on the median or the TIC with exclusion of very localized mass signals have been proposed (35-37). 

FIGURE 10.7 Profiles of radiolabeled metabolites in a rat bile sample determined by HPLC-MSC-MS. A majority of HPLC effluent (1 mL/min) was collected into 96-well microplates (four fractions per min) followed by radioactivity counting using TopCount. The top panel is the radiochromatogram of this sample. A potion of the effluent was analyzed by LTQ FTMS. The middle panel is the total ion chromatogram (TIC) from accurate mass full scan MS analysis. The bottom panel is a mass defect filter processed TIC (Zhu et al., 2006). The peak indicated is a GSH adduct that was not presented in the unprocessed TIC. 

The software records a mass spectrum for each scan to build up a 200-scan total ion chromatogram (TIC) count. The 200 scans can then be summed to give a mass spectrum for the experiment. 

Fig. 9.26. Schematic of the hybrid LIT-orbitrap instrument indicating the electrostatic potentials used in HCD and comparison of QD spectra, (a) HCD operation of the C-trap (b) with octopole collision ceU (c) CID spectrum of peptide [HLVDEPQNLIK+2H] ions from HCD as in (a) (d) spectrum as obtained by setup (b). NL intensity in counts normalized to 1 s TIC total ion current. Reproduced from Ref. [123] with permission. Nature Publishing Group, London, 2007.

---