Practical Protein Chemistry - A. Darbre 1989

Application of electron impact mass spectrometry for determining the amino acid sequence of peptides and proteins
Sample preparation methods
Acetylation

Treatment with acetic anhydride at room Temperature for one minute protects the α-amino group of the peptide, whereas treatment for three hours results in the complete Modification of the ε-amino groups. In the presence of a suitable base, both Amino groups are acetylated within approximately one minute. Two acetylation Procedures are outlined below, each suitable for modifying Peptides with an unknown Amino Acid Composition.

19.4.4.1. Prolonged acetylation. Dissolve the sample in 100 µL of Water, add 500 µL of a methanolic solution of acetic anhydride (3:1) to the solution, and allow the reaction mixture to stand for 3 h.

Excess Reagents are removed by evacuation under conditions where bumping of the reaction mixture is not observed.

19.4.4.2. Short-term acetylation. Dissolve the sample in 100 µL of sodium bicarbonate solution, prepared to contain 1 mg of salt per 1 mL of water, and after 30 s, add a solution of acetic anhydride in methanol (1:3). After approximately one minute, evacuate the reaction mixture first with a water-jet aspirator—taking precautions against potential bumping—and then with a forevacuum pump, or subject it to lyophilization.