Skip to main content

SOP-013: Sterile Filtration of Solutions

Purpose​

To sterilize cell culture solutions that cannot be autoclaved by passing them through a sterile membrane filter under aseptic conditions.

Scope​

This SOP applies to the sterile filtration of heat-sensitive cell culture reagents, media supplements, buffers, and stock solutions intended for mammalian cell culture.

Responsibilities​

The operator is responsible for:

  • Selecting an appropriate sterile filter.
  • Maintaining aseptic technique throughout the procedure.
  • Inspecting solutions before filtration.
  • Properly labeling and storing filtered solutions.

Required Materials​

Reagents​

  • Solution to be sterilized
  • 70% ethanol

Equipment​

  • Class II Biosafety Cabinet
  • Sterile membrane filter unit
  • Sterile collection bottle or tube
  • Sterile syringes (if using syringe filters)
  • Vacuum filtration system (if applicable)
  • Labels and laboratory marker

Procedure​

1. Prepare the Work Area​

Disinfect the biosafety cabinet work surface.

Assemble all required sterile materials before beginning the procedure.

2. Inspect the Solution​

Verify that the solution:

  • Is correctly prepared
  • Is free of visible particles or precipitates
  • Has not exceeded its expiry date

Do not filter solutions showing evidence of contamination.

3. Assemble the Filtration System​

Using sterile technique, assemble the appropriate filtration device according to the manufacturer's instructions.

Avoid touching sterile filter surfaces.

4. Filter the Solution​

Transfer the solution through the sterile membrane filter into a sterile collection vessel.

Avoid excessive pressure that may damage the membrane.

If filtration slows significantly, discontinue the procedure and replace the filter if necessary.

5. Label the Filtered Solution​

Label the container with:

  • Solution name
  • Concentration (if applicable)
  • Date of filtration
  • Expiry date (according to laboratory policy)
  • Operator initials

6. Store the Solution​

Store the filtered solution under the recommended conditions for that reagent.

Acceptance Criteria​

ParameterAcceptance Criterion
Solution appearanceClear and free of visible particles
FiltrationCompleted without leakage
Collection containerSterile and properly labeled
Final productNo visible contamination

Critical Control Points​

  • Perform filtration inside a certified Class II Biosafety Cabinet.
  • Use sterile, intact filter units.
  • Do not touch sterile filter components.
  • Do not exceed the manufacturer's recommended operating pressure.
  • Use the filtered solution only if sterility has been maintained throughout the procedure.

Documentation​

Record the following:

  • Date
  • Solution name
  • Volume filtered
  • Filter type (if required)
  • Storage conditions
  • Operator initials

Quality Control​

Verify:

  • Filter integrity before use.
  • Solution clarity after filtration.
  • Proper labeling.
  • Appropriate storage conditions.
  • No evidence of contamination.

Troubleshooting​

ObservationPossible CauseCorrective Action
Slow filtrationFilter becoming cloggedReplace the filter if necessary
Leakage during filtrationImproper assemblyReassemble using a new sterile filter if required
Visible particles after filtrationIncomplete filtration or contaminated solutionDiscard and prepare a fresh solution
Filter ruptureExcessive pressure appliedRepeat using a new filter and appropriate pressure

Safety Considerations​

  • Perform all procedures using aseptic technique in a certified Class II Biosafety Cabinet.
  • Wear appropriate personal protective equipment (PPE).
  • Treat all biological materials as potentially hazardous.
  • Dispose of used filters and consumables as biohazardous waste.
  • Clean and disinfect the work area after completing the procedure.