Karl Fischer Moisture, Titer and Reagent Consumption Calculator

Table of contents

• How to use
• Common mistakes
• Definitions
• Methodology
• Limitations & assumptions
• Sources

Volumetric Karl Fischer titration: A water test that measures the volume of Karl Fischer titrant needed to reach an endpoint.

Titrant titer: The water mass measured by 1 mL of titrant, reported as mg H2O/mL. It is found by standardizing the titrant with a known water amount. [1]

Endpoint: The point where the titrator detects that the Karl Fischer reaction is complete; its titrant volume is the endpoint volume.

Blank volume: Titrant used by background water from the solvent or setup rather than the sample. The calculator subtracts it from the endpoint volume.

Percent w/w: Water mass as a percent of total sample mass. The two masses must use the same mass basis.

ppm by mass: Parts per million by mass. For this calculation, 1% w/w equals 10,000 ppm.

Mistake: Entering the full endpoint reading as Water content (percent w/w) without subtracting background consumption.
Fix: Enter the separate blank run in Sample blank volume (mL) so the calculator can report Blank-corrected sample titrant volume.

Mistake: Entering a ppm specification while Expected water content unit is set to Percent w/w.
Fix: Match Expected water content unit to the specification before entering Expected water content ; 1% w/w equals 10,000 ppm.

Mistake: Using a reagent label value that is no longer current for Titrant titer (mg H2O/mL).
Fix: Use the current reagent record or calculate Calculated titrant titer from the latest standardization run.

Mistake: Setting Standard titrant volume (mL) equal to or below Standardization blank volume (mL).
Fix: Check both recorded readings. Standard titrant volume must be greater than the blank to calculate a titer.

Mistake: Treating Expected titrant use as the actual endpoint result.
Fix: Use it only to plan Planned sample mass (g) ; report a completed run from the measured endpoint and sample mass.

• This calculator is for volumetric Karl Fischer titration only. Coulometric Karl Fischer testing measures water differently and does not use a volumetric titrant titer.
• Blank correction uses the entered blank as a fixed volume. Follow the laboratory method for when and how a blank is measured.
• The moisture result assumes the sample mass, endpoint volume, blank volume, and current titrant titer are accurate.
• Planned titrant use and sample mass are estimates based on expected moisture. Side reactions, slow water release, atmospheric moisture, and sample handling can change the observed endpoint.
• Use mass-based inputs only. Do not enter sample volume as Sample mass (g) unless your approved method has already converted volume to mass.
• The calculator blocks a sample blank above its endpoint and a standard blank equal to or above its endpoint because those conditions do not produce a valid corrected volume.

Calculation steps

For a completed sample, the calculator first removes the measured background titrant use. It then converts corrected titrant volume to water mass using the current titer and divides by sample mass.

Blank-corrected sample volume (mL) = Titrant volume to endpoint (mL) - Sample blank volume (mL)

Water found in sample (mg) = Blank-corrected sample titrant volume (mL) x Titrant titer (mg H2O/mL)

Water content (% w/w) = Water found in sample (mg) / [Sample mass (g) x 1000] x 100

Water content (ppm by mass) = Water found in sample (mg) / [Sample mass (g) x 1000] x 1,000,000

For titer standardization, known water is divided by the blank-corrected titrant volume from the standard run.

Calculated titrant titer (mg H2O/mL) = Known water in standard (mg) / [Standard titrant volume (mL) - Standardization blank volume (mL)]

For planning, the calculator reads expected water content as the selected percent w/w or ppm value. A ppm entry is divided by 10,000 to convert it to percent w/w before calculating water mass, expected titrant use, and the mass needed for the chosen target volume.

Expected water in planned sample (mg) = Planned sample mass (g) x 1000 x expected percent w/w / 100

Expected titrant use (mL) = Expected water in planned sample (mg) / Titrant titer (mg H2O/mL)

Sample mass for desired titrant use (g) = Desired titrant volume (mL) x Titrant titer (mg H2O/mL) x 100 / [1000 x expected percent w/w]

Worked example

With a 5.0 mg H2O/mL titer, a 2.1 mL endpoint, a 0.1 mL blank, and a 1.0 g sample, corrected volume is 2.0 mL. Water found is 10 mg, so water content is 1.0% w/w or 10,000 ppm. For planning, 10.0 g at 0.1% w/w contains an estimated 10 mg water and is expected to use 2.0 mL of the same titrant.