Have you ever tried to compare filter paper between brands? Found a few cross-reference tables only to find out they contradict each others? You might have wondered how come nobody came up with a standard to describe grades and make sens of this mess?
When it comes to basic grades, the de-facto standard is Whatman, but what about the myriad of grades offered by other manufacturers that don't fit? The problem lies in the many parameters that define a filter paper, a lot more than what can be caracterized by flow or retention alone. Here is a non-exauhstive list of the main paper filter characteristics:
- media : While filter paper is made of pure cellulose, glass and quartz fiber filters are often referenced as filter 'paper'
- category : Qualitative and Quantitative can also be Hardened (chemical resistant or wet-strenghtened). Quantitative is normaly ashless (<0.01%) but can also be low-ash (<0.015%). Then there are technical filters for industrial use and those tailor made for a specific application.
- shape : Most common filters comes as discs to be used in a Buchner funnel but some applications like chromatography require sheets or bands. To improve speed in gravity filtration they can come pre folded as quadrants or pre-pleated as fluted filters.
