Water Content

What it determines

A weighed portion of sample is introduced into the titration cell, where iodine reacts with water in a fixed stoichiometry in the presence of sulfur dioxide, an alcohol, and a base. Iodine is consumed in direct proportion to the water present.

The iodine consumed at the endpoint corresponds directly to a mass of water. That mass is divided by the sample mass to give water content as a percentage. The cell is dried and blank-checked before the sample goes in, so drift from ambient moisture is accounted for.

Practical notes

• Lyophilized peptides take up moisture from the air within seconds of exposure, and the result will show it. A vial opened for weighing elsewhere carries that history into the lab.
• Sealed, unopened vials give the value the material actually left storage with.
• The titration consumes the aliquot taken for it.