Standard Operating Procedure for Water Analysis by Karl Fischer (KF) Titration in API Manufacturing
| Department | API Manufacturing |
|---|---|
| SOP No. | SOP/API/128/2025 |
| Supersedes | SOP/API/128/2022 |
| Page No. | Page 1 of 8 |
| Issue Date | 13/04/2025 |
| Effective Date | 15/04/2025 |
| Review Date | 13/04/2026 |
1. Purpose
To define a standardized procedure for the accurate determination of water content in pharmaceutical substances, excipients, and APIs using Karl Fischer (KF) titration, ensuring reproducibility and regulatory compliance.
2. Scope
This SOP is applicable to Quality Control laboratory personnel performing water content determination using Karl Fischer titration (volumetric or coulometric) for raw materials, intermediates, and final APIs.
3. Responsibilities
- QC Analyst: Perform the titration using validated procedure and record results accurately.
- QC Reviewer: Verify the water content value, reagent standardization, and calculations.
- QA Officer: Ensure documentation, compliance, and verification during audits.
4. Accountability
The Head – QC is accountable for ensuring that Karl Fischer analysis is conducted as per validated methodology, and all data are traceable and reviewed.
5. Procedure
5.1 Equipment and Reagents
- Karl Fischer titrator (volumetric or coulometric)
- Dry methanol (KF grade)
- KF reagent (e.g., Hydranal, Aquastar)
- Certified water standard (e.g., sodium tartrate dihydrate)
- Drying oven and desiccator (for sample preparation, if required)
5.2 Standardization of Karl Fischer Reagent
- Weigh ~100 mg of water standard (e.g., sodium tartrate dihydrate) into a clean dry titration vessel.
- Titrate using KF reagent until endpoint is reached.
- Calculate KF factor:
KF Factor = mg water / mL KF reagent consumed - Acceptable %RSD for three determinations: ≤ 2.0%
5.3 Sample Preparation
- Ensure sample is finely powdered and homogenous.
- Weigh accurately the sample (typically 10–200 mg based on expected moisture content).
- Transfer sample to the titration vessel using dry spatula or syringe (for liquid samples).
5.4 Titration Procedure
- Pre-titrate methanol blank before analysis.
- Introduce the weighed sample into the titration vessel and start titration.
- Allow the instrument to automatically reach the endpoint and display the volume used.
- Record the final volume of reagent and perform the calculation.
5.5 Calculation
- Use the formula:
% Water = (Volume of KF reagent × KF Factor × 100) / Weight of Sample (mg)
5.6 Precautions
- Handle KF reagents with care; avoid exposure to atmospheric moisture.
- Close reagent bottles immediately after use.
- Use gloves and eye protection while working with solvents and reagents.
- Do not reuse reagents once contaminated.
6. Abbreviations
- KF: Karl Fischer
- QC: Quality Control
- API: Active Pharmaceutical Ingredient
- RSD: Relative Standard Deviation
- % Water: Percent water content
7. Documents
- KF Titration Logbook (Annexure-1)
- Reagent Standardization Record
- Sample Analysis Report
8. References
- USP <921> – Water Determination
- ICH Q6A – Specifications
- 21 CFR Part 211 – US FDA GMP Guidelines
9. SOP Version
Version: 2.0
10. Approval Section
| Prepared By | Checked By | Approved By | |
|---|---|---|---|
| Signature | |||
| Date | |||
| Name | |||
| Designation | |||
| Department |
11. Annexures
Annexure-1: KF Titration Logbook
| Date | Sample Name | Batch No. | Sample Weight (mg) | Volume KF Used (mL) | KF Factor | % Water | Status |
|---|---|---|---|---|---|---|---|
| 13/04/2025 | API-XY | API-20250413 | 110 | 0.48 | 5.0 | 2.18 | Pass |
Revision History:
| Revision Date | Revision No. | Details | Reason | Approved By |
|---|---|---|---|---|
| 01/01/2022 | 1.0 | Initial Release | GMP Requirement | QA Head |
| 13/04/2025 | 2.0 | Included standardization, blank titration steps | Audit Update | QA Head |