Investigation of the mechanism of matrix adduct formation in MALDI at elevated pressure

Experiments were carried out to gain insight into the mechanism of matrix adduct formation in matrix-assisted laser desorption/ionization (MALDI) conducted at elevated pressures. Two theories of matrix adduct formation were considered: incomplete cluster evaporation and the so called 'poisoning' model. Both theories can qualitatively explain the influence of the ionization conditions, such as laser fluence, the buffer gas pressure and declustering voltage on the matrix adduct formation. The new set of experiments differentiates between the two models, and the results strongly support the 'poisoning' model.