Karl Fischer (KF) Apparatus Calibration: How To Perform Quickly

Karl Fischer (KF) calibration is performed by titrating a known water standard, such as 50–100 mg of disodium tartrate dihydrate (15.66% water) or a certified water standard. The methanol solvent is first neutralized, the standard is injected, and the result is verified to be within an acceptable range of the theoretical value.

Karl Fischer (KF) Apparatus Calibration

Karl Fischer (KF) apparatus calibration ensures accurate and reliable determination of moisture content by titrating certified water standards, such as disodium tartrate dihydrate (DST) or distilled water. During calibration, the KF solvent is first neutralized to eliminate background moisture. A known quantity of the standard is then added, and the titration is performed. The volume of Karl Fischer reagent consumed is recorded, and the KF factor (reagent concentration) is calculated. This procedure is repeated multiple times, and the average KF factor is established. Accurate calibration confirms that the instrument correctly measures actual water content and complies with GMP, pharmacopeial, and quality system requirements.

Reagents and instruments

• KF reagent
• Balance
• 10 ml Standard calibrated measuring cylinder
• KF Instrument
• Methanol
• Disodium tartrate standard (with valid COA)

Related: Pharmaceutical Analysis

General

For the smooth running of the KF instrument and to achieve precision, accuracy, and repeatability, the calibration of KF instrument is required.

Scope

This SOP procedure applies to all KF instruments of all departments of the company.

Responsibility

Research Scientists or Analysts responsible for the calibration of the instrument

HOD (Head of the department

To ensure the compliance of this SOP in the respective departments (ARD/CRD/QC/Production)

Frequency for KF calibration

Once in a month ± 3 days

Procedure for KF calibration

Burette calibration

1. Follow the operational SOP of the instrument
2. Place the burette in the 10 ml calibrated measuring cylinder
3. Press the start key and then switch on the enter key. Then again, press the start key
4. When the dispensing shows 3 m,l immediately press the stop key
5. Note down the observed volume of the KF reagent in the measuring cylinder
6. Now repeat the above steps 2, 3, 4 and 5 for 6 ml and 9 ml
7. Record the obtained volume and displayed volume in the following table-1

Table-1

Acceptance criteria

The volume displayed on the instrument and volume collected in the measuring cylinder should not vary more than 0.1ml; otherwise, follow the SOP

KF instrument calibration

• Follow the operational SOP for the operation of the instrument
• Weigh accurately about 100 mg of Disodium tartrate and transfer it into the titration vessel containing neutralised methanol, and test for water content as per operational SOP.
• Calculate the water by following formulae:

% Water=V×100×FW 

Where: V is the volume of KF consumed in ml, W in the weight of Disodium tartrate (in mg) and F is KF’s factor.

Tolerance limit

• The performance of the instrument is satisfactory if the difference between the obtained values within the tolerance limit of 15.66 ± 5% i.e 14.87% to 16.44% (otherwise follow the SOP)
• Repeat the above steps and take a total of five readings
• Record the result in the following table-2

Acceptance criteria

• RSD of five results should not be more than 1.0%

Table-2

Related:

• How To Determine Water by Karl Fischer (KF) Titration and How It Differs From LOD Testing
• How (KF) Karl Fischer Coulometric Titration Measures Water Content: Learn In 5 Minutes

FAQs

Abbreviations:

• HOD: Head of department
• Std: Standard
• SOP: Standard operating procedure
• COA: Certificate of analysis
• ml: Millilitre
• KF: Karl Fisher
• RSD: Relative standard deviation
• mg: miligram

Reference

• <921> WATER DETERMINATION