Mixed cellulose ester, WME range, circles. 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.
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 black mixed cellulose esters are available plain for automatic colony counting applications. 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.