SOP for Water Content Method Development Using Karl Fischer Titration in the AMD Laboratory
| Department | Analytical Method Development |
|---|---|
| SOP No. | SOP/AMD/047/2025 |
| Supersedes | SOP/AMD/047/2022 |
| Page No. | Page 1 of 14 |
| Issue Date | 19/05/2025 |
| Effective Date | 20/05/2025 |
| Review Date | 19/05/2026 |
1. Purpose
This SOP outlines the standardized procedure for the development and validation of methods to determine water content using Karl Fischer (KF) titration in the Analytical Method Development (AMD) department. The method ensures accuracy, specificity, and compliance with pharmacopeial standards.
2. Scope
This SOP applies to Karl Fischer titration methods (volumetric or coulometric) used to quantify water content in APIs, excipients, intermediates, and pharmaceutical formulations within the AMD laboratory.
3. Responsibilities
- Analytical Chemist: Develops the method, performs calibration and validation, and records all data.
- Reviewer: Verifies instrument calibration, calculations, and compliance with validation criteria.
- QA: Reviews and approves method validation documentation.
- Head – AMD: Authorizes final method approval and ensures regulatory alignment.
4. Accountability
The Head of AMD is accountable for ensuring that KF methods are scientifically developed, validated, and approved for use in regulatory filings and internal release testing.
5. Procedure
5.1 Method Selection
- Choose Volumetric KF for moisture range > 0.1%.
- Use Coulometric KF for moisture < 0.1% or trace analysis (μg levels).
- Select:
- Reagent: Hydranal® Composite 5 or equivalent
- Solvent: Methanol (dry, KF-grade)
- Titrant: Pyridine-free reagent unless justified
5.2 Instrument Calibration and Verification
- Verify instrument performance daily using sodium tartrate dihydrate as standard (water content 15.66%).
- Document calibration in Annexure-1: KF Instrument Calibration Log.
5.3 Sample Preparation
- Use 50–300 mg sample depending on expected water content.
- Handle hygroscopic substances under inert conditions (e.g., dry box or desiccator).
- Use airtight syringes or spatulas to transfer the sample into the KF cell.
- Record sample weight and preparation details in Annexure-2: Sample Analysis Sheet.
5.4 Titration Procedure
- Ensure background drift rate < 20 μg/min before starting.
- Initiate blank titration with methanol.
- Add sample to reaction vessel and start titration.
- Wait for the instrument to reach endpoint automatically.
- Result is displayed directly as % water content or ppm depending on configuration.
- Repeat analysis in duplicate and calculate mean.
5.5 Method Optimization
- Conduct trials to determine:
- Sample size suitability
- Reagent compatibility
- Solvent solubility
- Temperature and humidity impact
- Document optimization data in Annexure-3: KF Method Development Worksheet.
5.6 Method Validation
- Perform validation as per ICH Q2(R1):
- Specificity: Demonstrate selectivity for water (no interference from other volatiles).
- Accuracy: Perform spike recovery (added known water volumes).
- Precision: RSD ≤ 2% for six replicates.
- Linearity: Prepare standard additions and calculate r² ≥ 0.999.
- Robustness: Evaluate slight changes in drift rate or reagent concentration.
- Document all validation results in Annexure-4: KF Validation Summary.
6. Abbreviations
- KF: Karl Fischer
- LOD: Limit of Detection
- RSD: Relative Standard Deviation
- AMD: Analytical Method Development
- QA: Quality Assurance
7. Documents
- KF Instrument Calibration Log – Annexure-1
- Sample Analysis Sheet – Annexure-2
- KF Method Development Worksheet – Annexure-3
- KF Validation Summary – Annexure-4
8. References
- USP <921> – Water Determination
- ICH Q2(R1) – Validation of Analytical Procedures
- Ph. Eur. 2.5.12 – Water: Micro Determination
- 21 CFR Part 211 – Laboratory Controls
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 Instrument Calibration Log
| Date | Standard Used | Theoretical Value (%) | Observed Value (%) | Analyst |
|---|---|---|---|---|
| 02/05/2025 | Sodium Tartrate Dihydrate | 15.66 | 15.63 | Rajesh Kumar |
Annexure-2: Sample Analysis Sheet
| Date | Sample Name | Sample Weight (mg) | Water Content (%) | Analyst |
|---|---|---|---|---|
| 03/05/2025 | API-X | 125.6 | 0.72 | Sunita Reddy |
Annexure-3: KF Method Development Worksheet
| Trial No. | Solvent | Sample Size (mg) | Drift Rate | Water % | Conclusion |
|---|---|---|---|---|---|
| 1 | Methanol | 100 | 15 μg/min | 0.72 | Suitable |
Annexure-4: KF Validation Summary
| Parameter | Acceptance Criteria | Result | Status |
|---|---|---|---|
| Precision | RSD ≤ 2% | 1.2% | Pass |
| Accuracy | 98–102% | 99.5% | Pass |
| Specificity | No interference observed | Confirmed | Pass |
Revision History:
| Revision Date | Revision No. | Details | Reason | Approved By |
|---|---|---|---|---|
| 04/05/2025 | 2.0 | Updated titration conditions and validation protocol | Audit Compliance |