How to perform calibration of Karl Fischer (KF) Apparatus

Table of contents

• Reagents and instruments
• Responsibility
• Frequency 
• Burette calibration procedure
• KF Instrument Calibration

Calibration Description

Reagents and instruments

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

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 Chemist or Analyst 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 start key
4. When the dispensing shows 3 ml immediately press the stop key
5. Note down the observed volume of the KF reagent in the measuring cylinder
6. Now repeat 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 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

Abbreviations:

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

References:

• USP