Timeframe Dependent Fragment Ions Observed in In-Source Decay Experiments with β-Casein Using MALDI MS

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Biochemistry

Background:

• Matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) is a technique for peptide fragmentation.
• Time-of-flight (TOF) and quadrupole ion trap (QIT) TOF mass spectrometers (MS) offer different ion manipulation capabilities.
• Understanding fragmentation mechanisms is crucial for protein and peptide analysis.

Purpose of the Study:

• To compare fragment ion generation in TOF MS and QIT-TOF MS using MALDI-ISD.
• To elucidate the fragmentation pathways influenced by ion residence time and instrument design.
• To investigate the fragmentation of phosphorylated analytes like β-casein and its model peptide.

Main Methods:

• MALDI-ISD experiments were performed on β-casein and a model peptide.
• Fragment ions were analyzed using both TOF MS and QIT-TOF MS.
• Low-energy collision-induced dissociation (CID) experiments were conducted for confirmation.

Main Results:

• QIT-TOF MS produced a broader range of fragment ions (c-, z'-, z-ANL, y-, b-ions) compared to TOF MS (c-, z'-, z-ANL, y-, w-ions).
• Extensive fragmentation in QIT-TOF MS is attributed to ion injection into the QIT, long ion residence time (140 ms), and low-energy CID.
• Loss of phosphoric acid (98 u) was observed and explained by charge-independent ergodic fragmentation.

Conclusions:

• QIT-TOF MS provides more comprehensive fragmentation data for phosphorylated peptides via MALDI-ISD.
• Ion residence time and internal energy deposition significantly influence fragmentation pathways.
• The study clarifies the distinct fragmentation behaviors of different mass spectrometry instruments in analyzing phosphorylated biomolecules.