applies to the Analytical Method Development (AMD) department and microbiological laboratories involved in sample preparation and microbial enumeration using membrane filtration techniques for water, APIs, and dosage forms.

3. Responsibilities

• Microbiologist: Conducts filtration, monitors flow rate, and assesses recovery performance.
• Analytical Scientist: Coordinates validation of membrane compatibility and analyte retention.
• QA Officer: Verifies method optimization steps and validates all logs and records.
• Head – AMD: Approves final optimization protocol and ensures suitability across applications.

4. Accountability

The Head of Analytical Method Development is accountable for ensuring the optimized filtration method is robust, validated, and integrated into analytical testing programs.

5. Procedure

5.1 Selection of Membrane Type

1. Choose 0.45 µm cellulose nitrate or mixed cellulose ester (MCE) membrane filters for microbial analysis.
2. Use 0.2 µm PTFE or PVDF membranes for sterilizing filtration of chemical analytes.
3. Assess filter diameter (usually 47 mm or 90 mm) based on sample load and application.
4. Record membrane specifications in Annexure-1: Membrane Selection Log.

5.2 Equipment Setup and Sanitization

1. Sanitize filtration units (manifold, holders, funnels) with 70% IPA and UV exposure before use.
2. Assemble filtration apparatus in a laminar airflow (LAF) cabinet to maintain aseptic conditions.
3. Ensure proper sealing of membrane on base supports to avoid bypass leakage.

5.3 Filtration Procedure

1. Filter a known volume (typically 100 mL) of the sample through the membrane using vacuum filtration.
2. Rinse membrane with 100 mL of sterile 0.1% peptone water or buffer (if required for neutralization).
3. For microbiological testing, transfer membrane to:
   • TSA for bacterial enumeration
   • SDA for fungal enumeration
4. For chemical analysis, collect filtrate and test for analyte retention or loss.
5. Log filtration details in Annexure-2: Filtration Record Sheet.

5.4 Optimization Parameters

1. Evaluate flow rate: Acceptable range is 20–100 mL/min depending on viscosity and pore size.
2. Validate microbial recovery using standard spiked solutions:
   • Recovery should be 50%–200% for microbial cultures (e.g., E. coli, S. aureus)
3. For chemical tests, assess analyte recovery by comparing pre- and post-filtration concentrations.
4. Record findings in Annexure-3: Recovery Validation Log.

5.5 Acceptance Criteria

1. Filtration must be complete within 10 minutes for 100 mL of aqueous samples.
2. No clogging or channeling of membranes should be observed.
3. Recovery rates should meet the acceptance range as defined in the validation protocol.

5.6 Documentation and Final Report

1. Summarize results including flow rates, membrane integrity, and analyte recovery.
2. Include graphs or photographs as applicable (e.g., microbial growth on membranes).
3. Compile and approve optimization protocol in Annexure-4: Method Optimization Summary.

6. Abbreviations

• MCE: Mixed Cellulose Ester
• PVDF: Polyvinylidene Difluoride
• PTFE: Polytetrafluoroethylene
• LAF: Laminar Airflow
• CFU: Colony Forming Units
• SOP: Standard Operating Procedure

7. Documents

1. Membrane Selection Log – Annexure-1
2. Filtration Record Sheet – Annexure-2
3. Recovery Validation Log – Annexure-3
4. Method Optimization Summary – Annexure-4

8. References

• USP <61> – Microbial Enumeration
• USP <1227> – Validation of Microbial Recovery
• ICH Q2(R1) – Validation of Analytical Procedures

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name
Designation
Department

11. Annexures

Annexure-1: Membrane Selection Log

Membrane Type	Pore Size	Diameter	Application	Selected By
MCE	0.45 µm	47 mm	Microbial Enumeration	Sunita Reddy

Annexure-2: Filtration Record Sheet

Sample ID	Volume	Filter Type	Start Time	End Time
FIL-129-01	100 mL	MCE 0.45 µm	10:00 AM	10:06 AM

Annexure-3: Recovery Validation Log

Organism/Analyte	Pre-Filtration Value	Post-Filtration Value	% Recovery	Status
E. coli	95 CFU	88 CFU	92.6%	Pass

Annexure-4: Method Optimization Summary

Membrane filtration method optimized using MCE 0.45 µm membranes. Recovery validated for E. coli, S. aureus, and P. aeruginosa. Flow rate and recovery met acceptance criteria. Method ready for routine use and validation.

Revision History:

Revision Date	Revision No.	Details	Reason	Approved By
04/05/2025	2.0	Incorporated chemical compatibility and flow rate benchmarks	Annual SOP Review