Dissolved peptides are less stable than the lyophilizates. The solutions are best aliquoted before freezing to avoid thawing-refreezing cycles stressing the peptide. Solution stability depends on the type of solvent and the pH (pH 5-7 is considered as optimum). Peptides containing Asn, Gln, Cys, Met, Trp, Tyr tend to be less stable. Stock solutions of peptide substrates are best prepared in dry organic solvents to avoid premature hydrolysis.

The stability of the aliquots may range from weeks to months.