Standard Operating Procedure for Optimization of Salt Gradient in IEX during Biosimilar Manufacturing

Department	Biosimilars
SOP No.	SOP/BS/162/2025
Supersedes	SOP/BS/162/2022
Page No.	Page 1 of 10
Issue Date	04/05/2025
Effective Date	06/05/2025
Review Date	04/05/2026

1. Purpose

To establish a standard procedure for the optimization of salt gradients in ion-exchange chromatography (IEX) for biosimilar purification, enabling effective separation of product, variants, and impurities under GMP-compliant conditions.

2. Scope

This SOP applies to downstream processing of biosimilar products using both cation and anion exchange chromatography techniques where salt gradient elution is applied during intermediate or polishing steps.

3. Responsibilities

• Process Development: Design and execute salt gradient optimization experiments.
• Production: Apply validated gradients in GMP runs and record outcomes.
• QA: Review optimization protocols and ensure documentation compliance.

4. Accountability

The Head of DSP Development is accountable for finalizing gradient conditions and transferring them to GMP operations post-validation.

5. Procedure

5.1 Preliminary Setup

1. Select IEX column (e.g., SP Sepharose, Q Sepharose) and equilibrate as per respective SOPs.
2. Prepare gradient buffers:
   • Buffer A: 20 mM Tris-HCl, pH 8.0 (no salt)
   • Buffer B: 20 mM Tris-HCl, pH 8.0 + 500 mM NaCl
3. Set up chromatography system to allow accurate linear or stepwise gradient programming.

5.2 Gradient Design

1. Determine gradient range based on prior scouting runs or known isoelectric points (pI) of product.
2. Common gradients:
   • 0–100 mM NaCl (to elute weakly bound impurities)
   • 100–300 mM NaCl (to elute product fraction)
   • 300–500 mM NaCl (to clear strongly bound contaminants)
3. Set flow rate (e.g., 100 cm/hr) and gradient slope (e.g., 5% buffer B per column volume).

5.3 Gradient Execution

1. Initiate gradient elution and monitor UV (280 nm), conductivity, and pressure.
2. Collect fractions at fixed intervals or by peak detection.
3. Analyze fractions by SDS-PAGE, HCP ELISA, protein concentration, or SEC-HPLC.

5.4 Optimization Evaluation

1. Plot chromatogram and overlay product and impurity profiles.
2. Determine:
   • Resolution between product and impurity peaks
   • Gradient slope efficiency
   • Fractional recovery of target protein
3. Document findings in Annexure-1: Gradient Optimization Log.

5.5 Finalization and Transfer

1. Once optimal gradient range is identified, finalize buffer compositions and gradient profile.
2. Prepare GMP-scale equivalency run using validated parameters.
3. Transfer finalized procedure to manufacturing and document approval in Annexure-2.

6. Abbreviations

• IEX: Ion Exchange Chromatography
• GMP: Good Manufacturing Practice
• SEC-HPLC: Size-Exclusion Chromatography – High Performance Liquid Chromatography
• ELISA: Enzyme-Linked Immunosorbent Assay

7. Documents

1. Gradient Optimization Log – Annexure-1
2. GMP Transfer Summary – Annexure-2

8. References

• ICH Q8 – Pharmaceutical Development
• WHO TRS 999 – Biotherapeutic Manufacturing Guidance
• OEM Application Notes – GE Healthcare, Repligen, Bio-Rad

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name
Designation
Department

11. Annexures

Annexure-1: Gradient Optimization Log

Date	Batch No.	Gradient Range	Peak Resolution	Yield (%)	Comments
04/05/2025	BS-DEV-024	100–300 mM NaCl	1.8	92%	Accepted

Annexure-2: GMP Transfer Summary

Final Gradient Range	Buffer A Composition	Buffer B Composition	Flow Rate	Approved For GMP	Date
0–500 mM NaCl	20 mM Tris-HCl, pH 8.0	Tris + 500 mM NaCl	120 cm/hr	Yes	04/05/2025

Revision History:

Revision Date	Revision No.	Details	Reason	Approved By
04/05/2025	2.0	Added SEC-HPLC analysis and GMP transfer log	Process validation alignment