51
be done in classical atmospheric pressure ionizations, such as ESI, by direct infusion, or by using ambient mass spectrometry techniques, such as DESI, DART, LTP,
REIMS, PSI, etc.
The simultaneous introduction of many analytes in the ion source gives a molecular fingerprint of the sample and it is very effective for rapid screening analyses.
On the other hand, it can have some drawbacks, such as ion suppression phenomena, presence of isobaric species, need of a high dynamic range, difficulty to detect
trace molecules.
3.5 Identification, Confirmation and Quantitation
of Analytes by Mass Spectrometry
Depending on the information we are interested in, different mass spectrometry
approaches and strategies, using MS, high resolution mass spectrometry and tandem mass spectrometry, can be followed for identification, confirmation and quantitation of different compounds in complex matrices.
3.5.1 Structural Characterization and Identification
of Unknowns: Untarget Analysis
In a discovery phase of a study in many fields, such as metabolomics [17], proteomics [18], toxicology [19], and many others, for structurally characterize and
identifying unknowns without any preliminary information, an untarget analysis has
to be performed.
An untargeted profiling shows the presence of all ionizable and detectable analytes and it can be advantageous for novel marker and toxin discovering. Further,
this approach permits retrospective analysis of data based on a-posteriori hypothesis.
On the other hand, low abundance compounds might be likely missed because
ion suppression or obscuration by background signals from the matrix.
In mass spectrometry untarget analysis, two main methods can be used: Data
Dependent Acquisition or Data Independent Acquisition methods.
3.5.1.1 Data Dependent Acquisition (DDA)
In Data Dependent Acquisition a full MS scan is performed and ions are ranked by
their intensities and/or charges. Then, according to user defined criteria, software
applies automated real-time decisions for subsequent HRMS/MS
n
analysis (Fig. 3.2).
A user-defined criterion might be: for ions exceeding a signal threshold, a highresolution mass spectrum in a narrow m/z range followed by MS
2
or MS
n
product
ion scans have to be performed. To avoid repeating the same experiment for the
3 Mass Spectrometry Methods for Food Safety/Detection of Toxins in Food
be done in classical atmospheric pressure ionizations, such as ESI, by direct infusion, or by using ambient mass spectrometry techniques, such as DESI, DART, LTP,
REIMS, PSI, etc.
The simultaneous introduction of many analytes in the ion source gives a molecular fingerprint of the sample and it is very effective for rapid screening analyses.
On the other hand, it can have some drawbacks, such as ion suppression phenomena, presence of isobaric species, need of a high dynamic range, difficulty to detect
trace molecules.
3.5 Identification, Confirmation and Quantitation
of Analytes by Mass Spectrometry
Depending on the information we are interested in, different mass spectrometry
approaches and strategies, using MS, high resolution mass spectrometry and tandem mass spectrometry, can be followed for identification, confirmation and quantitation of different compounds in complex matrices.
3.5.1 Structural Characterization and Identification
of Unknowns: Untarget Analysis
In a discovery phase of a study in many fields, such as metabolomics [17], proteomics [18], toxicology [19], and many others, for structurally characterize and
identifying unknowns without any preliminary information, an untarget analysis has
to be performed.
An untargeted profiling shows the presence of all ionizable and detectable analytes and it can be advantageous for novel marker and toxin discovering. Further,
this approach permits retrospective analysis of data based on a-posteriori hypothesis.
On the other hand, low abundance compounds might be likely missed because
ion suppression or obscuration by background signals from the matrix.
In mass spectrometry untarget analysis, two main methods can be used: Data
Dependent Acquisition or Data Independent Acquisition methods.
3.5.1.1 Data Dependent Acquisition (DDA)
In Data Dependent Acquisition a full MS scan is performed and ions are ranked by
their intensities and/or charges. Then, according to user defined criteria, software
applies automated real-time decisions for subsequent HRMS/MS
n
analysis (Fig. 3.2).
A user-defined criterion might be: for ions exceeding a signal threshold, a highresolution mass spectrum in a narrow m/z range followed by MS
2
or MS
n
product
ion scans have to be performed. To avoid repeating the same experiment for the
3 Mass Spectrometry Methods for Food Safety/Detection of Toxins in Food