Mass
spectrometry
identify amount and type
of chemicals in a sample
in a high-vacuum region
(10^-5 - 10^-8 Torr)
• generation of gaseous ions
from analyte molecules
• ions separation according to
their m/z ratio
• ions detection as a function
of the m/z ratio
mass spectrum: relative abundance of
ions plotted as function on their m/z ratio
basic concept
unfragmented ion
DESTRUCTIVE METHOD
- TIC: one acquires a mass spectrum over a wide range of m/z ratios (50 to 2000). after the computer sums all signals at all m/z values in each spectrum.
- SIM: you set the MS acquisition in a narrow m/z interval (<10 u), which contains that of the analyte of interest.
- EIC: a SIM-track-like chromatogram can also be constructed from a TIC acquisition by requiring the computer to extract from the total MS spectra only the intensity relative to the ion with the desired m/z ratio.
CALIBRATION
external standard
internal standard
The sample is enriched with one or more known amounts of a standard solution of the analyte. Measurements are made on the sample and the sample in which the standard analyte solution has been added, then the responses are used to calculate the analyte concentration, assuming a linear relationship.
A known amount of a reference species is added to all samples, standards and blanks.
Than the analyte/reference signal ratio is reported as a function of analyte concentration in the standards.
ionization
CI
APCI
ESI
APPI
FAB
MALDI
DESI/DART
MS imaging
soft ionization tcq
low energy
EI
molecular ion
hard ionization tcq
high energy
radical ion that has the same molecular mass as the neutral molecule.
It produces high-energy radical cations, which give fragments at lower m/z and thus a large number of peaks in the spectrum.
Produces low-energy molecular fragments, which give little fragmentation and thus few peaks in the spectrum. Provides accurate molecular mass information, but multiple measurement runs through spatially or temporally coupled tandem MS systems are required.
In each spectrum the peak of greatest intensity, called the base peak, is taken as a reference and has arbitrary value = 100. The heights of the other peaks are calculated as percentages of the intensity of the base peak.