Impulse-driven heated-droplet deposition interface for capillary and microbore LC-MALDI MS and MS/MS

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Chromatography

Background:

• Direct matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) can suffer from ion suppression and limited sensitivity.
• Coupling liquid chromatography (LC) with MALDI-MS offers improved separation and detection capabilities for complex biological samples.
• Existing interfaces often struggle to accommodate the varying flow rates of different LC separation modes (capillary vs. microbore).

Purpose of the Study:

• To develop and validate an automated off-line interface for coupling capillary and microbore LC separations with MALDI MS and MS/MS.
• To assess the interface's performance in terms of sensitivity, chromatographic integrity, and mitigation of ion suppression.
• To demonstrate the interface's utility for analyzing complex peptide and protein samples, including phosphopeptides.

Main Methods:

• Development of an automated off-line LC-MALDI interface combining analyte concentration via heated hanging droplets and impulse-driven droplet deposition.
• Coupling of capillary LC (<5 µL/min) and microbore LC (up to 50 µL/min) with MALDI-time-of-flight (TOF) and quadrupole-TOF MS.
• Performance evaluation using peptide and protein standards, including [GLU1]-fibrinopeptide B, cytochrome c tryptic digest, and alpha-casein phosphopeptides.

Main Results:

• Detection of [GLU1]-fibrinopeptide B down to 5 fmol using microbore LC and MALDI-TOF MS with no significant band broadening.
• Successful mitigation of ion suppression, enabling detection of 100 fmol of [GLU1]-fibrinopeptide B in the presence of excess cytochrome c digest.
• High sequence coverage (82%) and detection of all nine phosphoserine residues in alpha-casein tryptic digests analyzed with LC-MALDI MS/MS.

Conclusions:

• The developed impulse-driven heated-droplet interface provides a flexible and automated solution for coupling diverse LC formats with MALDI MS.
• The interface enhances sensitivity and reduces ion suppression, enabling the detection of low-abundance peptides and complex post-translational modifications.
• This technology offers versatile MALDI analysis options for peptides and proteins, adaptable to specific research needs regarding information, speed, and sample size.