rheological testing and document data as per the method.

QC Supervisor: Review and approve test results.

QA Officer: Ensure SOP compliance and adherence to validation protocols.

4. Accountability

The Head of Quality Control is accountable for proper implementation and adherence to this SOP.

5. Procedure

5.1 Equipment

• Brookfield Viscometer or Equivalent Rheometer
• Temperature-controlled sample holder (if required)
• Calibrated stopwatch
• Disposable sample containers

5.2 Calibration and Verification

1. Ensure that the viscometer/rheometer is calibrated as per the instrument SOP before testing.
2. Verify spindle type and speed setting based on product rheological range.
3. Document calibration log in equipment register.

5.3 Sample Preparation

1. Collect representative samples (approx. 50 g) of gel from each batch.
2. Ensure sample is homogeneous and free from air bubbles.
3. If testing temperature-sensitive products, equilibrate to 25°C ± 2°C.

5.4 Test Parameters

• Viscosity Measurement: Measured in centipoise (cP) or Pa·s
• Thixotropy: Time-dependent shear thinning
• Yield Stress: Minimum stress required to initiate flow
• Flow Curve Analysis: Stress vs. shear rate profile

5.5 Test Execution

1. Mount appropriate spindle and set speed (e.g., Spindle No. 6 at 10 RPM).
2. Fill sample container up to indicated mark without disturbing gel structure.
3. Start measurement and allow stabilization time of 30 seconds.
4. Record viscosity values at predefined intervals (e.g., 10, 20, 30, 60 sec).
5. Repeat at multiple speeds to determine thixotropic behavior if required.

5.6 Data Recording

All results should be entered into the Rheology Test Sheet (Annexure-1) along with sample details, instrument settings, and observations.

5.7 Acceptance Criteria

Compare results with specification limits as defined in the product specification file. Any deviation should be investigated and reported.

5.8 Precautions

• Do not reuse samples or spindles without proper cleaning.
• Ensure no entrapped air during filling as it affects reading accuracy.

6. Abbreviations

• SOP: Standard Operating Procedure
• QC: Quality Control
• RPM: Revolutions Per Minute
• cP: Centipoise

7. Documents

1. Rheology Test Sheet – Annexure-1
2. Viscometer Calibration Log – Annexure-2

8. References

• USP General Chapter 911 – Viscosity
• ICH Q6A Specifications Guidelines
• Instrument User Manual

9. SOP Version

Version: 2.0

10. Approval Section

	Prepared By	Checked By	Approved By
Signature
Date
Name
Designation	Jr. Production Chemist	QA Executive	Head – Manufacturing
Department	Gel Manufacturing	Quality Assurance	Manufacturing

11. Annexures

Annexure-1: Rheology Test Sheet

Product Name
Batch Number
Date of Testing
Spindle Used
RPM
Temperature
Viscosity (cP)
Thixotropy Observed
Analyst Name/Sign

Annexure-2: Viscometer Calibration Log

Calibration Date	Standard Used	Expected Viscosity	Observed Viscosity	Status (Pass/Fail)	Remarks

Revision History

Revision Date	Revision No.	Details	Reason	Approved By
08/05/2022	1.0	Initial version	New SOP Release	QA Head
02/06/2025	2.0	Included new viscosity parameters	Periodic Review	QA Head