Karl Fischer Titration: How Labs Measure the Water in a Freeze-Dried Peptide

A freeze-dried peptide looks completely dry, but it usually still holds a small percentage of water, and it can pull more from the air. How do labs measure it?

The method

Karl Fischer titration, developed by Karl Fischer in 1935, is a chemical reaction that consumes water in exact proportion. Iodine reacts with sulfur dioxide only when water is present. The lab adds iodine until the reaction stops and calculates the water from how much was used.

What results look like

Water content in lyophilized peptides is commonly a few percent of the weight, though it varies by peptide and how it was handled.

Why it matters for the label

A vial’s gross weight includes the peptide, counter-ions such as acetate or TFA, and water. Only the remainder is net peptide. So a 10 mg vial holds less than 10 mg of actual peptide.

Handling tips

• Let a cold vial warm to room temperature before opening, so moisture does not condense inside.
• Reseal promptly.
• Store dry and cold.

This applies to blends such as Nasal Wolverine 10mg too. Keep reading to learn how net content is checked.

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For laboratory research use only. Not for human or veterinary use, and not intended to diagnose, treat, cure or prevent any condition. This article is educational and is not medical advice.