Mass SpectrometryeBased Approach for Protein Biomarker Verification - Proteomic and Metabolomic Approaches to Biomarker Discovery - page 404

to further fragment the product ions monitored
in Q3. In MRM 3 , the ion chromatogram is recon-
structed from fragments of the product ion in
the linear ion trap instead of from the product
ionasintheMRMmode,asshownin Figure 3 .
The MRM 3 mode further reduces background
interferences, which lead to lower LOQs.
It was demonstrated that MRM 3

LOD and LOQ using five model proteins with

only a slight reduction of accuracy and preci-
sion compared to a conventional MRM assay.
The MRM 3

demonstrated its potential for

biomarker veri cation when it was applied to

quantitate PSA in plasma samples obtained
from three cancer patients using only a simple
solid phase extraction sample preparation step
targeted at PSA peptides. The low ng/ml

generally

resulted in three- to fivefold improvements in

FIGURE 3 Schematic representation of MRM 3 on a hybrid triple quadrupole linear ion trap mass spectrometer with
extracted ion chromatogram peak for quantitation. (Reproduced with permission from reference #23).