What is the difference between a total ion chromatogram and a selected ion chromatogram?
Just as an FID gives a response based on the number of ions formed as sample elutes from the column, so does GC/MS, in the form of a total ion chromatogram (TIC). The difference is that each point in the chromatogram is actually a mass spectrum. Conversely, a selected ion chromatogram can be retrieved for any mass.
What is a selected ion chromatogram?
Definition: A plot of ion current vs. retention time obtained from a chromatography experiment with mass detection. A small mass window is monitored such that the mass chromatogram represents detection of a very specific mass-to-charge ratio.
How does selective ion monitoring work?
Selected ion monitoring (SIM) is a mass spectrometry scanning mode in which only a limited mass-to-charge ratio range is transmitted/detected by the instrument, as opposed to the full spectrum range. This mode of operation typically results in significantly increased sensitivity.
What is an EIC chromatogram?
Extracted ion chromatogram (EIC) is created by plotting the intensity of the signal observed at chosen mass-to-charge value or series of values in a series of mass spectra recorded as a function of retention time.
What does a total ion chromatogram show?
The total ion current (TIC) chromatogram represents the summed intensity across the entire range of masses being detected at every point in the analysis. The range is typically several hundred mass-to-charge units or more.
Why do we need vacuum for MS instruments?
All mass spectrometers operate at very low pressure (high vacuum). This reduces the chance of ions colliding with other molecules in the mass analyzer. Any collision can cause the ions to react, neutralize, scatter, or fragment. All these processes will interfere with the mass spectrum.
What was the reason for using selected ion monitoring?
SIM is frequently used for the quantitative determination of specific analytes by MS, usually in combination with a chromatographic separation. The mass spectrometer is used to monitor a limited number of ions characteristic of target compounds, rather than to acquire a complete spectrum.
What advantages does selected ion monitoring offer over full scan mode in GC MS?
Selected ion monitoring The full scan mode is useful for qualitative detection, mass scouting and for studies on the fragmentation patterns of unknowns. On the other hand, selected ion monitoring helps in quantitative studies on the specific ions of interest in the spectra of compound (s) of your interest.
What is TIC chromatogram?
A TIC (Total Ion Chromatogram) is a chromatogram created by summing up intensities of all mass spectral peaks belonging to the same scan. The TIC is compared to a GC chromatogram. Note that the TIC includes background noise as well as sample components.
What is base peak chromatogram?
The base peak chromatogram is similar to the TIC chromatogram, however it monitors only the most intense peak in each spectrum. This means that the base peak chromatogram represents the intensity of the most intense peak at every point in the analysis.