What is the difference between 0.22μm and 0.2μm ?

2025-07-31 Eternalwater The difference between 0.22μm and 0.2μm primarily lies in naming conventions and industry applications, as both actually represent the same pore size grade and belong to the sterilizing-grade filtration category.
In the field of sterile filtration, 0.22μm and 0.2μm are two common nominal pore size ratings for sterilizing-grade filters. Although the numerical difference is minimal (only 0.02μm), their distinctions are mainly reflected in four aspects: historical evolution, standard definitions, retention capabilities and application validation.

Sterilizing-Grade Filters

1.Historical Evolution and Naming Origins

Pore Size	Background Description
0.22μm	The early industry habitual terminology originated in the 1970s. At that time, filtration technology was not mature, with actual filtration precision approximating 0.22μm, leading to its widespread adoption.
0.2μm	Modern standardized nomenclature, driven by international standards organizations (such as ASTM, ISO) and regulatory agencies (FDA, EU GMP), aims to unify precision requirements.
Key Points：0.22μm is essentially the "old name" of 0.2μm. The current international standard for sterilization-grade filters has been unified to 0.2μm (such as ASTM F838-05), but some companies still use the "0.22μm" label due to historical habits, and the actual product performance is consistent with 0.2μm

2.Key Differences in Retention Capability

Although the values are close, 0.2μm filters demonstrate superior retention for specific microorganisms, particularly the following challenge organisms:

Microorganisms	Minimum size	0.22μm filter	0.2μm filter
(Brevundimonas diminuta)	0.3–0.4μm	Potential breakthrough (old standard)	Complete retention（LRV≥7）
Mycoplasma	0.2–0.3μm	Higher risk	Highly efficient retention
LRV（Log Reduction Value）: Modern 0.2μm filters achieve LRV ≥7 for B. diminuta (i.e., ≤1 organism may pass per 10⁷ challenged), while traditional 0.22μm filters may only reach LRV ≥6.

3.Standards and Validation Methods

Project	0.22μm(old standard)	0.2μm(current standard)
Testing Standards	No unified method	ASTM F838-05(mandatory use of B. diminuta challenge）
Validation Resssquirements	Dependent on manufacturer-defined parameters	Requires 3 batches of bacterial challenge, each batch ≥10⁷ cfu/cm²
Pore Size Definition	Nominal	Absolute
Industry Consensus: Only filters compliant with ASTM F838-05 qualify as "sterilizing-grade", with a nominal 0.2μm pore size rating. Filters with a nominal 0.22 μm cannot guarantee the sterilizing capacity if they are not validated by this standard. ASTM F838-05(2013)--Standard Test Method for Determining Bacterial Retention of Membrane Filters Utilized for Liquid Filtration, published in 2005 by the American Society for Testing and Materials (US-ASTM)

4.Practical Application Selection

Scenarios	Recommended Selection		Reasons
Injections, vaccines, and other sterile preparations	0.2μm	Compliant with GMP and pharmacopeia mandatory standards (e.g., USP <71>)
Non-critical buffers, gas filtration	0.22μmor 0.2μm	lower risk and cost-effective
Bioreactor air intake, cell culture	0.2μm	Effective retention of small microorganisms like mycoplasma

Summary：Core Differences

Comparison Dimension	0.22μm	0.2μm
Essence	Traditional habitual terminology	International standard defined pore size
Retention Capacibility	May be insufficient (especially for B. diminuta )	Strictly guarantee LRV≥7 performance
Standard Compliance	May not fully comply with ASTM F838-05	ASTM F838-05 Mandatory ASTM F838-05 compliance
Regulatory Acceptance	May face regulatory scrutiny	Globally recognized standard
Practical Suggestions: Priority should be given to the filters with a nominal 0.2 μm and validated ASTM F838-05, regardless of whether they are labeled as "0.22μm". During actual procurement, request the bacterial challenge test report and integrity test limits for the filter rather than only focusing on the pore size value.