a) Can you draw structures of some very common MALDI matrices?
b) Try suggesting a suitable matrix. Sort out the mess in the table.
Polyacrylate Protein Oligosaccharide Polycyclic aromatic hydrocarbon Oligonucleotide Peptide Dithranol Sinapinic acid 2,5-Dihydroxybenzoic acid LDI sufficient 3-Hydroxypicolinic acid alpha-Cyano-4-hydroxy-cinnamic acid
c) Which sort of ions usually make up the largest portion of a matrix spectrum in positive-ion MALDI?
Ions formed by cationization or protonation of the matrix and their clusters are the major contributers to a matrix spectrum, i.e., [nM+H/Na/K]+ ions. Fragment ions and clusters resulting thereof also play a role.
d) What sample layer do you prefer in MALDI preparations? Large well-shaped crystals or microcrystalline deposition?
Microcrystalline deposition is by far superior: i) it offers better shot-to-shot reproducibility, because several crystallites are irradiated simultaneously, and ii) it is less prone to peak shifts, because the electric potential experienced by the ions does not vary so much.