Selecting Qualitative Filter Paper on Amazon.com

Qualitative filter paper is a type of laboratory filter made from cotton cellulose fibers and is typically used to clarify solutions for a broad range of laboratory and industrial applications. A qualitative filter is typically placed inside a filter funnel, Hirsch, or Büchner funnel to trap particles from liquid or gas within the fibers of the filter paper, allowing the filtered solution to be analyzed or used in further processes.

Filter paper is available in a range of grades that represent increasing levels of cellulose purity, surface hardness, and chemical resistance. Available in square or rectangular sheets or as discs, the filter paper can be flat or pre-pleated. Circular filters are designed in a variety of standard sizes, and range in diameter from 25mm to 500mm. Other factors to consider when choosing qualitative filter paper include the flow rate, loading capacity, retention value, thickness, and strength.

A qualitative filter can be designed to allow a slow, medium, or fast flow rate during filtration. To increase the flow rate and loading capacity, pre-pleated filter paper has a greater surface area to trap particles while maintaining filtration speed. Retention values can range between 2 and 40μm, and represent the maximum size of particles in liquid that can be trapped in that filter. A filter with slow flow and a particle retention value of 2.5μm will clarify cloudy solutions by trapping fine particles. A fast flowing filter with particle retention of 20-25μm can be used to retain course particles and gelatinous precipitates. Thickness can range from 140 to 420μm; thicker paper provides greater mechanical strength than thinner paper. Some filter paper contains a resin that, when wet, increases the filter's mechanical strength for filtration applications requiring vacuum or pressure.

Laboratory applications requiring qualitative filter paper include organic extractions and biological fluid separation processes. In industrial environments, it is used for air pollution and contaminant monitoring. Some agricultural applications include soil analysis and seed testing procedures. Manufacturers include Whatman.