Quantitative fluorescence measurements performed on typical matrix molecules in matrix-assisted laser desorption/ionisation

Fundamental photophysical parameters have been determined for several molecules that are commonly used as matrices, e.g. ferulic acid, within matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. Fluorescence quantum efficiencies (phi (qe)), singlet decay rates (k(1)), vibrationless ground-singlet transition energies and average fluorescence wavelengths have been obtained from solid and solution samples by quantitative optical measurements. This new data will assist in modelling calculations of MALDI processes and in highlighting desirable characteristics of MALDI matrices. phi (qe) may be as high as 0.59 whilst the radiative decay rate (k(f)) appears to be within the (0.8-4) x 10(8) s(-1) range. Interestingly, alpha -cyano-4-hydroxycinnamic acid (alpha -CHC) has a very low phi (qe) and fast non-radiative decay rate which would imply a rapid and efficient thermalisation of electronic excitation. This is in keeping with observations that alpha -CHC exhibits low threshold fluences for ion detection and the low fluences at which alpha -CHC tends to fragment. (C) 2000 Elsevier Science B.V. All rights reserved.