Matrix Assisted Laser Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) allows analysis of proteins and peptides with high sensitivity and soft ionization with little or no fragmentation. Ions are formed through gas-phase proton-transfer reactions with photoionized matrix molecules. Matrix is typically a small energy absorbing molecule such as alfa-cyano-4-hydroxycinnamic acid (for synthetic peptides) or sinapinic acid (for intact proteins).
MALDI-TOF MS analysis produces data for peptide and protein molecular weight determination. It is no longer used for protein identification by peptide mass fingerprinting as publication standards have become more stringent and require MS/MS data and statistical analysis for validating identifications.
Example MALDI-TOF linear mass spectrum of intact protein: Hg-Papain oligomerization