Karl Fischer titration measures water through its reaction with iodine and sulfur dioxide in the presence of a base and an alcohol. The coulometric form, which generates iodine electrically, suits the small sample sizes typical of peptides.
Water content is one of the components that, with the counter-ion, accounts for the difference between the weighed mass of a peptide and its net peptide content.
See also
For in vitro laboratory research only. Not for human or veterinary use. This library describes chemistry, analytical methods and published laboratory research; it gives no guidance on use in people or animals.