SOP for Moisture Determination in Hygroscopic Active Pharmaceutical Ingredients

Department	Analytical Method Development
SOP No.	SOP/AMD/062/2025
Supersedes	SOP/AMD/062/2022
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 establishes the procedure for the development, optimization, and validation of methods to determine moisture content in hygroscopic Active Pharmaceutical Ingredients (APIs). The methods include Karl Fischer (KF) titration, loss on drying (LOD), and thermogravimetric analysis (TGA), depending on API characteristics and moisture levels.

2. Scope

This SOP is applicable to the Analytical Method Development (AMD) department and is intended for use during early-stage method development, formulation compatibility studies, stability assessments, and routine QC evaluation of hygroscopic APIs.

3. Responsibilities

• Analytical Chemist: Conducts moisture determination trials, documents procedures and results.
• Reviewer: Verifies test execution, calculations, and ensures GMP-compliant documentation.
• QA Officer: Ensures adherence to regulatory standards and internal quality procedures.
• Head – AMD: Approves validated methods for routine and regulatory application.

4. Accountability

The Head of Analytical Method Development is accountable for ensuring that accurate, validated, and scientifically justified methods for moisture determination in hygroscopic APIs are developed and documented.

5. Procedure

5.1 Method Selection

1. Assess the physicochemical nature of the API:
   • If moisture level is < 1.0% or water is tightly bound, use Karl Fischer titration.
   • If water is loosely held and thermally stable, use Loss on Drying (LOD).
   • For detailed profiles, use Thermogravimetric Analysis (TGA).
2. Document selection rationale in Annexure-1: Method Selection Justification Log.

5.2 Equipment and Conditions

1. Karl Fischer:
   • Volumetric or coulometric KF titrator
   • Dried methanol and standard water solution (e.g., 1.0 mg/mL)
   • Use sample introduction via syringe or sealed vial to minimize atmospheric moisture exposure
2. LOD:
   • Moisture analyzer or drying oven
   • Standard temp: 105°C ± 2°C; time: 3–5 hrs or until constant weight
   • Use pre-weighed crucibles or dishes
3. TGA:
   • Thermogravimetric Analyzer
   • Heating rate: 10°C/min up to 300°C in nitrogen/air
   • Measure % weight loss across temperature zones
4. Log equipment details in Annexure-2: Equipment Calibration & Condition Log.

5.3 Sample Handling and Preparation

1. Handle hygroscopic samples inside desiccator or glove box if needed.
2. Accurately weigh the required quantity:
   • 2–10 mg for KF
   • 500–1000 mg for LOD
   • 5–10 mg for TGA
3. For LOD, use previously dried and tared crucibles.
4. Document weights and sample codes in Annexure-3: Sample Handling Record.

5.4 Execution of Moisture Analysis

1. Karl Fischer:
   • Run blank titration and standardization daily
   • Inject sample into the reaction vessel using dry syringe
   • Wait until titration end-point is reached (auto or visual)
   • Calculate % moisture = (mg water / sample weight) × 100
2. LOD:
   • Weigh sample + crucible (W1)
   • Dry at 105°C for 3–5 hours (or specified temp/time)
   • Cool in desiccator and weigh (W2)
   • Moisture (%) = [(W1 – W2) / Sample weight] × 100
3. TGA:
   • Program method and load sample
   • Run thermal scan from 30°C to 300°C
   • Record initial and final weight %
   • Interpret specific weight losses as moisture, degradation, or solvent loss
4. Record all observations in Annexure-4: Moisture Measurement Log.

5.5 Method Optimization

1. Evaluate:
   • Sample size sensitivity and reproducibility
   • End-point stability and moisture drift
   • Temperature dependency and sample degradation
2. Optimize weighing time, environmental controls, and drying parameters.
3. Document optimization in Annexure-5: Method Optimization Report.

5.6 Method Validation

1. Specificity: Ensure no interference from volatile solvents, excipients, or degradation products.
2. Precision: RSD ≤ 2.0% for 6 replicates.
3. Accuracy: Spike recovery for known moisture content materials (e.g., lactose monohydrate).
4. Linearity: Demonstrated using standards (0.1–1.0 mg H₂O for KF).
5. Robustness: Evaluate small changes in drying temp, time, or sample size.
6. Summarize in Annexure-6: Validation Summary Sheet.

6. Abbreviations

• API: Active Pharmaceutical Ingredient
• LOD: Loss on Drying
• KF: Karl Fischer
• TGA: Thermogravimetric Analysis
• SOP: Standard Operating Procedure
• RSD: Relative Standard Deviation

7. Documents

1. Method Selection Justification Log – Annexure-1
2. Equipment Calibration & Condition Log – Annexure-2
3. Sample Handling Record – Annexure-3
4. Moisture Measurement Log – Annexure-4
5. Method Optimization Report – Annexure-5
6. Validation Summary Sheet – Annexure-6

8. References

• USP <921> – Water Determination
• ICH Q2(R1) – Validation of Analytical Procedures
• EP 2.5.12 – Loss on Drying
• USP <731> – Loss on Drying

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name
Designation
Department

11. Annexures

Annexure-1: Method Selection Justification Log

API Name	Moisture Expected	Method Selected	Justification	Analyst
Citric Acid Anhydrous	< 0.5%	Karl Fischer	High accuracy for low moisture	Sunita Reddy

Annexure-2: Equipment Calibration & Condition Log

Instrument	ID	Last Calibration	Next Due	Status
Karl Fischer Titrator	KF-204	01/04/2025	01/10/2025	Calibrated

Annexure-3: Sample Handling Record

Sample Code	Weight Taken (mg)	Container Type	Analyst
API-2101	7.5 mg	Amber Glass Vial	Ajay Mehra

Annexure-4: Moisture Measurement Log

Trial	Technique	Reading (%)	Acceptance Limit (%)	Status
1	Karl Fischer	0.42%	≤ 0.5%	Pass

Annexure-5: Method Optimization Report

Parameter	Tested Variation	Impact	Conclusion
Drying Temp (LOD)	95°C vs 105°C	Slower drying at 95°C	Reject

Annexure-6: Validation Summary Sheet

Validation Parameter	Criteria	Result	Status
Accuracy	98–102%	99.6%	Pass
Precision	RSD ≤ 2%	1.1%	Pass
Linearity	R² ≥ 0.999	0.9993	Pass

Revision History:

Revision Date	Revision No.	Details	Reason	Approved By
04/05/2025	2.0	Added TGA methodology and expanded validation details	Annual SOP Review