title: Is energy pooling necessary in ultraviolet matrix-assisted laser desorption/ionization?
abstract: BACKGROUND
  Energy pooling has been suggested as the key process for generating the primary ions during ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI). In previous studies, decreases in fluorescence quantum yields as laser fluence increased for 2-aminobenzoic acid, 2,5-dihydroxybenzoic acid (2,5-DHB), and 3-hydroxypicolinic acid were used as evidence of energy pooling. This work extends the research to other matrices and addresses whether energy pooling is a universal property in UV-MALDI.
  
  
  METHODS
  Energy pooling was investigated in a time-resolved fluorescence experiment by using a short laser pulse (355 nm, 20 ps pulse width) for excitation and a streak camera (1 ps time resolution) for fluorescence detection.
  
  
  RESULTS
  The excited-state lifetime of 2,5-DHB decreased with increases in laser fluence. This suggests that a reaction occurs between two excited molecules, and that energy pooling may be one of the possible reactions. However, the excited-state lifetime of 2,4,6-trihydroxyacetophenone (THAP) did not change with increases in laser fluence. The upper limit of the energy pooling rate constant for THAP is estimated to be approximately 100-500 times smaller than that of 2,5-DHB.
  
  
  CONCLUSIONS
  The small energy pooling rate constant for THAP indicates that the potential contribution of the energy pooling mechanism to the generation of THAP matrix primary ions should be reconsidered.
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan.
authors.forename: Hou-Yu
authors.initials: HY
authors.lastname: Lin
authors.forename: Botao
authors.initials: B
authors.lastname: Song
authors.forename: I-Chung
authors.initials: IC
authors.lastname: Lu
authors.forename: Kuo-Tung
authors.initials: KT
authors.lastname: Hsu
authors.forename: Chih-Yu
authors.initials: CY
authors.lastname: Liao
authors.forename: Yin-Yu
authors.initials: YY
authors.lastname: Lee
authors.forename: Chien-Ming
authors.initials: CM
authors.lastname: Tseng
authors.forename: Yuan-Tseh
authors.initials: YT
authors.lastname: Lee
authors.forename: Chi-Kung
authors.initials: CK
authors.lastname: Ni
mesh_terms: D000098:Acetophenones / Q000737:chemistry; D005841:Gentisates / Q000737:chemistry; D013050:Spectrometry, Fluorescence / Q000295:instrumentation / Q000379:methods; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000295:instrumentation / Q000379:methods*; D014466:Ultraviolet Rays
chemical_list: D000098:Acetophenones; D005841:Gentisates; C107067:2,4,6-trihydroxyacetophenone; C010925:2,5-dihydroxybenzoic acid