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Karl Fischer Moisture Analysis

The reference method for quantifying water in lyophilized peptides. USP <921> coulometric and volumetric titration, 5–7 business day turnaround at an independent laboratory.

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Method

USP <921> Karl Fischer titration. Coulometric for water <1%, volumetric for higher content. Direct water quantification, not inferred from mass loss.

Sample size

20–50 mg lyophilized peptide for duplicate coulometric determination.

Quality system

Independent testing lab. DEA registered laboratory (#RA0571996).

Turnaround

5–7 business days from sample receipt.

Why Karl Fischer specifically

Moisture content in a lyophilized peptide is a direct predictor of shelf life. Residual water drives hydrolysis of the peptide backbone, promotes aggregation, and can depress the glass transition temperature enough that a stored cake collapses. Karl Fischer titration exploits a stoichiometric reaction between iodine and water, so the number reported reflects water and only water. Loss-on-drying methods can over-report by counting residual solvents; thermogravimetric methods struggle at the low percentages typical of quality lyophilized product.

For pharmaceutical release testing, USP <921> identifies Karl Fischer as the reference method for water determination. Regulators increasingly cite it where water is a critical quality attribute.

What to expect on the report

  • Sample identification and lot number
  • Method used (coulometric or volumetric) with USP <921> reference
  • Water content in mg/g and % w/w, with duplicate values and mean
  • Instrument model and calibration status
  • Analyst signature, report date, and method validation attestation
  • Raw data available on request

When to include Karl Fischer in your panel

Include

Lyophilized peptide release testing. Stability studies. Compounded sterile preparation incoming API QA. Method validation. Any time water content affects shelf life or biology.

Skip

Aqueous formulations where water is the solvent. Exploratory work where degradation is not yet a concern. Situations where loss-on-drying is specified by an existing monograph.

Karl Fischer is often bundled with HPLC purity, endotoxin (LAL), heavy metals, and residual solvents in a full injectable release panel. Full pricing lives at purity testing cost.

Karl Fischer Moisture Analysis: FAQ

Karl Fischer titration is the reference method for quantifying water content in a sample. It works by a specific chemical reaction between iodine and water in the presence of sulfur dioxide, methanol, and a base. Because the reaction stoichiometry is exact, the technique measures water directly rather than by inference from mass loss. USP <921> is the compendial method.

Residual water in a lyophilized peptide drives hydrolysis, promotes aggregation, and can lower the glass transition temperature so the cake collapses in storage. Well-freeze-dried peptides typically show under 5% water, and premium grades under 2%. Above 5% and shelf life drops noticeably.

Coulometric Karl Fischer measures trace water below 1% with high accuracy and is the standard for lyophilized peptides. Volumetric Karl Fischer suits samples with water content above 1% and is used for hydrated APIs, some solvents, and formulation intermediates. We select the method based on the expected range.

20 to 50 mg of lyophilized peptide is typically sufficient for a coulometric determination in duplicate. Smaller amounts are possible with adjustments.

Loss on drying measures total volatile loss (water + solvents + volatile impurities). Karl Fischer measures water specifically. Regulatory monographs increasingly specify Karl Fischer where water content is critical because loss on drying can over-report by counting residual solvents.

Standard turnaround for Karl Fischer moisture analysis is 5 to 7 business days from sample receipt. Turnaround is the same whether the test is run standalone or as part of a broader release panel.

Water content is a critical quality attribute for APIs used in compounded sterile preparations. Whether Karl Fischer is required depends on the finished dosage form and the pharmacy's quality system, but it is common on the incoming API specification.

Standalone Karl Fischer typically runs $150 to $300 per sample. Bundled with purity and identity in a full release panel, the marginal cost is lower. Request a quote at acslabtest.com/get-quote.

Ready to Get Started?

Contact us today for a free consultation and customized quote for your peptide testing needs.

(561) 513-8435cpierre@acslabtest.com