Selecting a 13 mm or 25 mm Vacuum Filter Holder 

For microscopic particle analysis, effective filtration area (EFA) can be just as important as membrane diameter. EFA determines how concentrated retained particles will be on the membrane surface. If the filtration area is too large for a sample with few particles, particles may be spread out and difficult to locate. If the area is too small for a sample with a high particle load, particles may overlap and become difficult to distinguish. Estimating the expected particle load can therefore help determine the appropriate EFA—and filter holder—for downstream analysis. 

When selecting a holder, it is also important to understand what its stated size represents. For example, Sterlitech's 13 mm glass microanalysis holders use the same 25 mm membrane discs as 25 mm holders but expose a smaller portion of the membrane to the sample. As a result, particles are concentrated over a smaller area, which can affect preparation and subsequent microscopic analysis. 

Membrane diameter and effective area are distinct specifications 

Membrane diameter and effective filtration area (EFA) describe two different aspects of a filter holder. Membrane diameter determines the size of the disc required for the holder, while EFA describes the portion of that membrane actually exposed to the sample during filtration. 

For example, holders with a 13 mm EFA use 25 mm membranes but expose only 1.2 cm² of filtration area. In comparison, holders with a 25 mm EFA that uses the same 25 mm diameter membrane provide a larger effective area of 2.1 cm². Aside from the membrane diameter, a membrane filter holder’s EFA also plays a role in considering which membrane filter holder to use. 

Match Effective Filtration Area to Particle Load 

Effective filtration area influences how densely particles are distributed across the membrane surface. For the same number of retained particles, a smaller effective filtration area concentrates particles into a smaller footprint. Based on the assembly specifications, a 1.2 cm² effective area produces approximately 1.75 times the average particle density of a 2.1 cm² area. 

For samples with low particle concentrations, this increased density can make particles easier to locate and reduce the membrane area that must be inspected or mapped. However, when particle loads are higher, concentrating particles within a smaller area can lead to crowding, overlapping particles, and faster membrane fouling. 

Consider the expected particle load when selecting an effective filtration area. If particles are likely to become too concentrated for downstream analysis, reduce the sample volume or select a holder with a larger effective filtration area. 

For analytical techniques such as FTIR microscopy or laser direct infrared imaging (LDIR), also consider membrane material, effective filtration area, and mounting requirements to ensure compatibility with the instrument workflow. 

Glass Microanalysis Filter Holders Comparison:

Once you have selected an effective area, compare the available models by membrane support and funnel capacity. Use the table below to verify effective filtration area of the membrane filter holders from Rocker Scientific, Advantec and Sterlitech.

Choose for the measurement specific to your feed and particle load 

Start with the analytical endpoint: retained particles or collected filtrate. For particle examination with minimal particle load, choose a membrane filter holder that will concentrate the particles in a smaller membrane filtration area such as: 

• 13mm Glass Microanalysis Holder & 1000ml Funnel, KG 13 C | Sterlitech 
• 13mm Glass Microanalysis Holder, Frit Support, 250mL, 25mm | Sterlitech 
• 13mm Glass Microanalysis Holder, 500mL, KG 13 B, 25mm | Sterlitech 
• 13mm Glass Microanalysis Holder & 100ml Funnel, KG 13 A | Sterlitech 

For higher particle load samples suspended in a small volume of feed, choose a large membrane filter area that maximizes flow, retention, and overall throughput. These filter holders come highly recommended: 

• All-Glass Filtration Assembly, Glass frit, GFA 25 | Sterlitech 
• All-Glass Filtration Assembly, Stainless steel, GFS 25 | Sterlitech 
• Rocker Scientific VF5 Glass Filtration Set, 15mL, 25mm | Sterlitech 
• Rocker Scientific VF8 Glass Filtration Set, 15mL, 25mm | Sterlitech 

A smaller exposed area does not establish lower holdup volume or better recovery. Check model-specific data and verify performance with your sample. Explore Sterlitech’s vacuum filter holders, or share your membrane, sample volume, particulate load, and downstream method with our technical team to help select an appropriate assembly. 

References: 

1. Sterlitech Glass Filter Holders and Assemblies Product Specification Sheet 
2. Rocker VF8 & VF5 Technical Data Sheet 
3. Advantec Glass Microanalysis Holders Data Sheet.pdf