Answer 11.2

a) Can you draw structures of some very common MALDI matrices?

Common MALDI matrices

b) Try suggesting a suitable matrix. Sort out the mess in the table.

Analyte

Polyacrylate

Protein

Oligosaccharide

Polycyclic aromatic hydrocarbon

Oligonucleotide

Peptide

Matrix

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.