Whatman mixed cellulose ester membranes are composed of cellulose acetate and cellulose nitrate. These membranes are characterized by a smoother and more uniform surface than pure nitrocellulose filters.

• Sterile options available for critical applications
• Excellent contrast for easier particle detection
• Grids are nontoxic and do not inhibit bacterial growth, ensuring sample integrity
• Black plain and black gridded membranes have a mix of cellulose nitrate and cellulose acetate
• The membrane offers a high degree of internal surface area for greater adsorption of product
• Higher dirt loading capacity
• Biologically inert with good thermal stability
• No surfactants to contaminate samples
• Uniform microporous structure of membrane gives high flow rates

The color contrast provided by the filter surface facilitates particle detection and minimizes eye fatigue. The ME range has a lower cellulose acetate content compared to the WME range of membranes.

In microbiological colony counting procedures, the color contrast between the surface and the colonies facilitates the counting process.

Many microbiological techniques include colony counting after incubation as the standard method of quantitation. Whatman gridded filters have clearly defined grid lines spaced at 3.1 mm or 5 mm intervals. The special ink used is nontoxic and completely free from bacterial growth inhibitors. Whatman black mixed cellulose esters are available plain for automatic colony counting applications, as well as gridded to assist in manual counting procedures. Black membranes provide contrast between residue or cell colors and the filter without having to counter-stain the membrane.

For those laboratories preferring to use membranes sterilized by autoclaving for microbiological work, Whatman provides black gridded membranes in packs with pads ready for laboratory autoclaving.