a) How is sensitivity defined in mass spectrometry?
The sensitivity is the slope of a plot of analyte amount versus signal strength. In mass spectrometry, sensitivity is reported as ionic charge of a specified m/z reaching the detector per mass of analyte used. The sensitivity is given in units of C µg–1 for solids.
For gaseous analytes, it can be specified as the ratio of ion current to analyte partial pressure in units of A Pa–1.
b) What is the meaning of the term detection limit?
The limit of detection (LOD) or detection limit states the lowest amount of sample that can yield a signal just good enough for reliable detection. The LOD depends on the compound, its state (pure, in solution, component of a complex mixture), the type of instrument, and its modes of operation (ionization method and scan mode).
c) Do you know the meaning of the acronyms TIC and RIC?
The total ion current (TIC) can either be measured by a hardware TIC monitor before mass analysis, or it can be reconstructed by the data system from the spectra after mass analysis. The TIC represents a measure of the overall intensity of ion production or of mass spectral output as a function of time, respectively. The TIC obtained by means of data reduction, i.e., by mathematical construction from the mass spectra as successively acquired while the sample evaporates, is also termed total ion chromatogram (TIC). For this purpose, the sum of all ion intensities belonging to each of the spectra is plotted as a function of time or scan number, respectively.
The term reconstructed ion chromatogram (RIC) is used to describe the intensity of a given m/z or m/z range plotted as a function of time or scan number.
d) What are the potential uses of TICs and RICs?
Plotting RICs is especially useful to identify a target compound of known m/z from complex TICs. RICs allow to extract at what time during a measurement the target compound is eluted. RICs can also be used to uncover the relationship of certain m/z values to different mass spectra obtained from the measurement of a single (impure) sample.