Continuous flow reduced-pressure infrared laser desorption/ionization mass spectrometry

Area of Science:

• Analytical Chemistry
• Mass Spectrometry
• Spectroscopy

Background:

• Continuous flow infrared laser desorption/ionization (IR-LDI) offers matrix-free ionization and contaminant tolerance.
• A key limitation of IR-LDI is poor sensitivity due to inefficient ion transfer at atmospheric pressure.

Purpose of the Study:

• To investigate the effect of ion source pressure on sensitivity in continuous flow IR-LDI.
• To identify optimal pressure conditions for enhanced ion signal intensity.

Main Methods:

• A novel continuous flow IR-LDI method was developed using a frit plate and a tunable mid-IR laser.
• Samples were injected directly without matrices into a variable-pressure ion source (21-101 kPa).

Main Results:

• Reducing ion source pressure from 101 kPa to 71 kPa increased angiotensin II [M+H]+ signal intensity by 1.8-fold.
• Optimal pressure reduction was more effective at lower laser pulse energy and ion source temperature.
• Insulin [M+2H]2+ and [M+3H]3+ signals increased by 1.4-fold and 1.1-fold, respectively, at reduced pressures.

Conclusions:

• The optimal ion source pressure for IR-LDI was investigated for the first time.
• A slight reduction in ion source pressure demonstrably enhances sensitivity.
• Findings are applicable to other IR laser-based ambient ionization techniques.