57
different molecules. Combining SIM with retention time increases selectivity as
very few molecules, if not one, will yield the same ions and will have the same
retention time. Owing to the large diffusion of tandem mass spectrometry instruments, the use of SIM is actually limited in low resolution analysis but it is widely
used in high resolution MS.
Tandem mass spectrometry methods, and in particular selected reaction monitoring (SRM), also known as multiple reaction monitoring (MRM), are widely used in
target analysis. In selected reaction monitoring, typically occurring in triple quadrupole mass spectrometers, both analyzers don’t make any scan but are fixed at given
m/z values: the first at the m/z value of the precursor ion, the latter at m/z value of the
product ion (Fig. 3.8). By monitoring one or more reactions for a single analyte, a
SRM analysis is much more specific and selective than monitoring just single ions
as it occurs in SIM. Furthermore SRM offers highly sensitive, and cost-effective
analysis for simultaneous quantitation of several hundreds of targeted compounds in
a single experiment.
Parallel reaction monitoring (PRM) [30] is also included in this group, being
related to SRM, even if it can be used also in untarget analysis (Fig. 3.8).
As in a SRM assay, also in parallel reaction monitoring the first analyzer selects
specific ions of interest for fragmentation. Unlike SRM/MRM, the second analyzer
is not fixed on a given m/z value, but it scans over a wide m/z range so to detect all
fragment ions at once (Fig. 3.8). Parallel reaction monitoring has been firstly set up
on Q Exactive mass spectrometer having a quadrupole followed by an Orbitrap
analyzer [30], but it has been used also with a ToF as a second analyzer.
So in PRM no any reaction pathway has to be defined, saving time in method
development, and the use of high resolution and accurate mass measurements is an
advantage when analyzing analytes in complex mixtures.
3.6 Food Safety/Detection of Toxins in Food
Toxins are represented by wide classes of molecules with different chemico- physical
properties, ranging from volatile small molecules to polar big molecules, such as
proteins. Among other analytical methods, mass spectrometry plays a key role and
it is widely applied in the field of food safety for detecting and quantifying contaminants, residues and toxins in food [16, 31–35].
A targeted approach with data independent acquisition mode is aimed to detect
the presence/absence of already known and well characterized contaminants, residues and toxins in food and it is limited to a user built compound list.
As an example, liquid chromatography coupled to mass spectrometry operating
in multiple reaction monitoring with triple quadrupole instruments has been traditionally selected for mycotoxin analysis, monitoring in parallel quantitative and
qualitative ion transitions. This approach provides both high sensitivity and high
selectivity, and achieves limits of regulatory requirements for the official control
methods. Anyway the method set-up is tedious and time-consuming when wanting
to determine a large number of substances [36].
3 Mass Spectrometry Methods for Food Safety/Detection of Toxins in Food
different molecules. Combining SIM with retention time increases selectivity as
very few molecules, if not one, will yield the same ions and will have the same
retention time. Owing to the large diffusion of tandem mass spectrometry instruments, the use of SIM is actually limited in low resolution analysis but it is widely
used in high resolution MS.
Tandem mass spectrometry methods, and in particular selected reaction monitoring (SRM), also known as multiple reaction monitoring (MRM), are widely used in
target analysis. In selected reaction monitoring, typically occurring in triple quadrupole mass spectrometers, both analyzers don’t make any scan but are fixed at given
m/z values: the first at the m/z value of the precursor ion, the latter at m/z value of the
product ion (Fig. 3.8). By monitoring one or more reactions for a single analyte, a
SRM analysis is much more specific and selective than monitoring just single ions
as it occurs in SIM. Furthermore SRM offers highly sensitive, and cost-effective
analysis for simultaneous quantitation of several hundreds of targeted compounds in
a single experiment.
Parallel reaction monitoring (PRM) [30] is also included in this group, being
related to SRM, even if it can be used also in untarget analysis (Fig. 3.8).
As in a SRM assay, also in parallel reaction monitoring the first analyzer selects
specific ions of interest for fragmentation. Unlike SRM/MRM, the second analyzer
is not fixed on a given m/z value, but it scans over a wide m/z range so to detect all
fragment ions at once (Fig. 3.8). Parallel reaction monitoring has been firstly set up
on Q Exactive mass spectrometer having a quadrupole followed by an Orbitrap
analyzer [30], but it has been used also with a ToF as a second analyzer.
So in PRM no any reaction pathway has to be defined, saving time in method
development, and the use of high resolution and accurate mass measurements is an
advantage when analyzing analytes in complex mixtures.
3.6 Food Safety/Detection of Toxins in Food
Toxins are represented by wide classes of molecules with different chemico- physical
properties, ranging from volatile small molecules to polar big molecules, such as
proteins. Among other analytical methods, mass spectrometry plays a key role and
it is widely applied in the field of food safety for detecting and quantifying contaminants, residues and toxins in food [16, 31–35].
A targeted approach with data independent acquisition mode is aimed to detect
the presence/absence of already known and well characterized contaminants, residues and toxins in food and it is limited to a user built compound list.
As an example, liquid chromatography coupled to mass spectrometry operating
in multiple reaction monitoring with triple quadrupole instruments has been traditionally selected for mycotoxin analysis, monitoring in parallel quantitative and
qualitative ion transitions. This approach provides both high sensitivity and high
selectivity, and achieves limits of regulatory requirements for the official control
methods. Anyway the method set-up is tedious and time-consuming when wanting
to determine a large number of substances [36].
3 Mass Spectrometry Methods for Food Safety/Detection of Toxins in Food