Standard Operating Procedure for pH Adjustment of Bulk Protein Solution in Biosimilar Manufacturing

Department	Biosimilars
SOP No.	SOP/BS/182/2025
Supersedes	SOP/BS/182/2022
Page No.	Page 1 of 9
Issue Date	04/05/2025
Effective Date	06/05/2025
Review Date	04/05/2026

1. Purpose

To provide a controlled procedure for the adjustment of pH in bulk biosimilar protein solutions after purification, ensuring product quality, stability, and compliance with GMP standards.

2. Scope

This SOP applies to all batches of biosimilar bulk drug substance requiring pH adjustment before formulation or bulk storage within the downstream processing area.

3. Responsibilities

• Production: Perform pH adjustment as per batch record and record all data in real-time.
• QC: Provide calibrated pH meters and verify accuracy of final pH values.
• QA: Review and approve pH adjustment log and ensure batch meets release criteria.

4. Accountability

The Downstream Manufacturing Manager is accountable for the correct execution and documentation of pH adjustment procedures.

5. Procedure

5.1 Preparation

1. Verify the product-specific target pH range in the BMR (e.g., 6.0–6.5).
2. Ensure availability of calibrated pH meter, sterile pH probes, and pre-approved acid/base reagents (e.g., 0.1N HCl or 0.1N NaOH).
3. Confirm volume of protein solution to be adjusted and temperature equilibration (15–25°C recommended).

5.2 pH Measurement

1. Immerse the pH probe into the sample container with continuous gentle stirring.
2. Record initial pH and compare against the specification range.

5.3 pH Adjustment

1. If adjustment is required:
   • Use sterile syringe or peristaltic pump to add 0.1N acid/base dropwise.
   • After each addition, allow thorough mixing (at least 2 minutes) and recheck pH.
   • Continue until pH falls within the specified range.
2. Record the exact volume of acid/base used in Annexure-1.

5.4 Final Verification

1. Confirm final pH from three separate readings within 2 minutes.
2. Ensure homogeneity by sampling from top and bottom of the tank.

5.5 Precautions

1. Never add acid and base simultaneously.
2. Use only filtered and validated pH adjusting solutions.
3. Avoid excessive adjustment that may impact protein stability.

6. Abbreviations

• pH: Potential of Hydrogen
• BMR: Batch Manufacturing Record
• GMP: Good Manufacturing Practice
• QC: Quality Control

7. Documents

1. pH Adjustment Log – Annexure-1
2. Final pH Verification Record – Annexure-2

8. References

• ICH Q8 – Pharmaceutical Development
• FDA Guidance on Protein Drug Stability
• WHO TRS 999 – GMP for Biotherapeutics

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name
Designation
Department

11. Annexures

Annexure-1: pH Adjustment Log

Time	Initial pH	Reagent Used	Volume Added (mL)	Adjusted pH	Operator
10:00	6.7	0.1N HCl	2.5	6.4	Ajay Verma

Annexure-2: Final pH Verification Record

Sample Point	Reading 1	Reading 2	Reading 3	Average pH	Result
Top	6.4	6.4	6.3	6.37	Pass
Bottom	6.3	6.4	6.4	6.37	Pass

Revision History:

Revision Date	Revision No.	Details	Reason	Approved By
04/05/2025	2.0	Added homogeneity verification and reagent handling steps	Audit compliance