Is energy pooling necessary in ultraviolet matrix-assisted laser desorption/ionization?

Area of Science:

• Analytical Chemistry
• Physical Chemistry

Background:

• Energy pooling is hypothesized as the primary ion generation mechanism in ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI).
• Previous studies inferred energy pooling from decreased fluorescence quantum yields in specific matrices under increasing laser fluence.
• This research investigates the universality of energy pooling across different UV-MALDI matrices.

Purpose of the Study:

• To determine if energy pooling is a universal phenomenon in UV-MALDI.
• To investigate the role of energy pooling in the excited-state dynamics of different matrix compounds.
• To assess the contribution of energy pooling to primary ion formation in UV-MALDI.

Main Methods:

• Utilized time-resolved fluorescence spectroscopy with a 355 nm, 20 ps laser pulse for excitation.
• Employed a streak camera with 1 ps time resolution for precise fluorescence detection.
• Investigated energy pooling by analyzing changes in excited-state lifetimes at varying laser fluences.

Main Results:

• Observed a decrease in the excited-state lifetime of 2,5-dihydroxybenzoic acid (2,5-DHB) with increasing laser fluence, supporting energy pooling.
• Found no change in the excited-state lifetime of 2,4,6-trihydroxyacetophenone (THAP) with increasing laser fluence.
• Estimated the energy pooling rate constant for THAP to be 100-500 times smaller than that for 2,5-DHB.

Conclusions:

• Energy pooling is not a universal mechanism in UV-MALDI across all matrices.
• The minimal energy pooling rate constant for THAP suggests its limited role in primary ion generation.
• Reevaluation of the energy pooling mechanism's contribution to THAP matrix ion formation is warranted.