Spectrus: Differences in peak areas between TIC and Individual Ion Traces

Description
In xC/UV/MS data, the total ion chromatogram (TIC) and extracted ion chromatograms (XICs) are based on different signal definitions:

• TIC integrates intensity over all m/z values at each time point.
• XIC integrates intensity over a selected m/z (or narrow m/z window) at each time point.

As a result, the peak area measured in a TIC will usually not match the peak area measured in an XIC, even for the same component.

Solution

1. Understand what each trace represents:
   • TIC: sum of intensities of all ions detected at each scan.
   • XIC: intensity of one specific ion (or small m/z range) at each scan.
2. When quantifying a particular compound:
   • Prefer the XIC for the compound’s characteristic m/z (or isotopic cluster) rather than the TIC.
   • Note:
     • The TIC peak will generally have a larger area (it includes background and other ions).
     • The XIC peak area corresponds only to the chosen m/z window.