and formulated drug products.

2. Scope

This SOP is applicable to all method optimization work involving laser diffraction techniques within the Analytical Method Development (AMD) department. It covers dry and wet analysis, dispersion optimization, repeatability studies, and span analysis.

3. Responsibilities

• Analytical Scientist: Develops and optimizes the method, selects conditions, and evaluates results.
• Instrument Operator: Performs instrument calibration, setup, and measurements.
• QA Officer: Ensures compliance with documentation and analytical guidelines.
• Head – AMD: Approves the optimized method protocol for further validation.

4. Accountability

The Head of Analytical Method Development is accountable for scientific accuracy, reproducibility, and compliance of the optimized laser diffraction method.

5. Procedure

5.1 Instrument Setup and Calibration

1. Switch on the laser diffraction instrument (e.g., Malvern Mastersizer) and allow stabilization.
2. Perform background calibration using manufacturer guidelines.
3. Validate the alignment, cleanliness of sample cell, and laser intensity baseline.
4. Check that the software version is compatible with lab systems.
5. Log in Annexure-1: Instrument Calibration Record.

5.2 Selection of Analysis Mode

1. Choose between:
   • Dry Dispersion: For non-hygroscopic, flowable powders
   • Wet Dispersion: For poorly flowable or cohesive materials
2. Select appropriate dispersion unit (e.g., Aero S for dry or Hydro EV for wet).
3. Record analysis mode and justification in Annexure-2: Mode Selection Log.

5.3 Optimization of Dispersion Parameters

1. Identify optimal dispersion conditions:
   • Obscuration between 10–20%
   • Sonication (wet) or air pressure (dry) to minimize agglomeration
   • Stirrer speed (wet: 500–2500 rpm)
2. Conduct trials to determine:
   • Lowest span value with reproducible D10, D50, D90
   • Minimal variation across replicates (RSD < 3%)
3. Log trials in Annexure-3: Dispersion Optimization Summary.

5.4 Refractive Index Settings

1. Select appropriate refractive index (RI) and absorption values based on compound class:
   • Standard RI values: API (1.60–1.65), Excipients (1.45–1.55)
2. If unknown, conduct trial runs with estimated values and confirm with microscopy data.
3. Document in Annexure-4: RI Configuration Log.

5.5 Repeatability and Robustness Testing

1. Perform a minimum of six repeat measurements (same sample, same day).
2. Calculate mean, standard deviation, and %RSD for D10, D50, and D90.
3. Perform same-day and inter-day robustness by varying dispersion time or stirring speed.
4. Evaluate shift in span and curve consistency.
5. Record data in Annexure-5: Repeatability and Robustness Log.

5.6 Method Acceptance Criteria

1. Accept method if:
   • D50 values are consistent (RSD < 3%)
   • Span < 2.0 for mono-modal distributions
   • Obscuration stable across runs
2. Document final optimized parameters in Annexure-6: Final Method Sheet.

6. Abbreviations

• D10, D50, D90: Particle diameter at 10%, 50%, and 90% cumulative volume
• PSD: Particle Size Distribution
• RI: Refractive Index
• RSD: Relative Standard Deviation
• SOP: Standard Operating Procedure

7. Documents

1. Instrument Calibration Record – Annexure-1
2. Mode Selection Log – Annexure-2
3. Dispersion Optimization Summary – Annexure-3
4. RI Configuration Log – Annexure-4
5. Repeatability and Robustness Log – Annexure-5
6. Final Method Sheet – Annexure-6

8. References

• USP <429> – Light Diffraction Measurement of Particle Size
• ICH Q2(R1) – Validation of Analytical Procedures
• Instrument Manufacturer’s Method Optimization Guidelines

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name
Designation
Department

11. Annexures

Annexure-1: Instrument Calibration Record

Date	Instrument	Calibration Status	Performed By
18/05/2025	Mastersizer 3000	Pass	Sunita Reddy

Annexure-2: Mode Selection Log

Wet dispersion selected for sample PSD-116 due to cohesive nature and aggregation in dry conditions.

Annexure-3: Dispersion Optimization Summary

Trial	Stir Speed	Sonication	D50	Span
1	1500 rpm	Yes	7.4	1.8

Annexure-4: RI Configuration Log

Sample	RI Used	Absorption	Source
API-B	1.60	0.01	Manufacturer Data

Annexure-5: Repeatability and Robustness Log

Run	D50	Span	Obscuration
1	7.3	1.9	12%
2	7.4	1.8	13%

Annexure-6: Final Method Sheet

Method: Wet laser diffraction using Mastersizer 3000, water + 0.1% Tween 80, stirrer 1800 rpm, 60 s measurement, RI: 1.60, Absorption: 0.01. Acceptable D50 and span confirmed over 6 replicates.

Revision History:

Revision Date	Revision No.	Details	Reason	Approved By
04/05/2025	2.0	Expanded robustness testing and added RI configuration	Annual Review