SOP-004: Centrifuge Stability Testing

1. Purpose

This procedure establishes the protocol for using centrifugal force to rapidly screen emulsion stability. Centrifuge testing accelerates gravitational separation to predict long-term phase behavior.

2. Scope

This SOP applies to emulsion-based cosmetics during development for rapid prototype screening. Centrifuge testing supplements but does not replace real-time or accelerated stability testing.

3. Test Conditions

Parameter	Standard Condition	Notes
Speed	3,000-5,000 RPM	Higher RPM = more stress
Duration	15-30 minutes	Longer = more stress
Temperature	Room temperature (20-25°C)	Unless otherwise specified
Sample Volume	10-15 mL typical	Use appropriate tubes

4. Equipment Requirements

Laboratory centrifuge capable of 3,000-5,000 RPM
Appropriate centrifuge tubes (15 mL or 50 mL)
Balance for counterweighting tubes
Timer
PPE: safety glasses, lab coat

Safety Warning: Never operate a centrifuge with unbalanced loads. Always use matched pairs of tubes with equal weights. Imbalanced centrifuges can cause injury and equipment damage.

5. Procedure

Document initial appearance of product before testing
Transfer sample to appropriate centrifuge tube (fill to recommended level)
Prepare a counterweight tube with equal mass (water or second sample)
Place tubes in opposing positions in centrifuge rotor
Set RPM and timer according to test conditions
Start centrifuge and allow to reach target speed
After completion, allow rotor to stop completely before opening
Carefully remove tubes without disturbing contents
Immediately observe and document separation patterns
Test re-emulsification by gentle inversion or shaking

6. Interpretation

Observation	Interpretation	Action
No visible separation	Stable emulsion	Pass - proceed to long-term testing
Slight creaming, re-emulsifies easily	Marginally stable	Consider reformulation
Clear separation, requires vigorous mixing	Unstable	Reformulate before further testing
Complete phase separation	Highly unstable	Major reformulation required

Limitations: Centrifuge testing is a screening tool only. Passing centrifuge does not guarantee long-term stability. Failing centrifuge indicates the need for reformulation before investing in long-term studies.

Product Name:
Batch/Lot Number:
Date of Test:
Centrifuge Model:
RPM Used:
Duration:	_______ minutes
Temperature:	_______ °C

Separation Observed:	☐ None ☐ Slight ☐ Moderate ☐ Severe
Type of Separation:	☐ Creaming (oil rises) ☐ Sedimentation (particles sink) ☐ Both ☐ N/A
Re-emulsifies on Shaking:	☐ Yes, easily ☐ Yes, with effort ☐ Partially ☐ No
Pass/Fail:	☐ Pass ☐ Fail

Appearance Before:
Appearance After: