What is ash-free filter paper for

Filter paper

Microphoto of a paper coffee filter. The cellulose fibers can be clearly seen. Pore ​​size of the unsized paper around 5 µm.
Commercially available round filters for laboratory use

Filter paper and filters made from paper-like materials are used in many fields to separate solids from liquids or gases; physically, to separate a solid phase from an aqueous or gaseous one.

application areas

  • In the household
  • In motor vehicles
  • In chemical and biological laboratories
    • solid / liquid: numerous applications with special filter papers (see below)

Use in the chemistry laboratory

In the chemical laboratory, filter paper is important for preparative and analytical work.[1]. Papers with different pore sizes have been developed for the various purposes:[2]

Filter shapes and pore sizes

Filter papers are considered flat for the different funnel shapes Round filter or as pre-folded Pleated filter executed.

Depending on the application, papers with different pore sizes are used, which are identified by color codes:

  • Black band filter serve for coarse precipitation (fast filtration)
  • White band filter serve for finer precipitates (medium-fast filtration)
  • Blue band filter serve for very fine precipitates (slow filtration)

Ashless filter paper

Ash-free filters burn up practically residue-free when a filtered precipitate is dried and incinerated and thus does not influence the sample weight during gravimetric analytical work, as is the case with conventional filters.

Use in the biology laboratory

Round filters are used here, but not for filtering, but for keeping z. B. of small-cut parts of plants in preparative work. As a rule, round filters of the appropriate size are placed in Petri dishes for this purpose.

Individual evidence

  1. Brockhaus ABC chemistry, VEB F. A. Brockhaus Verlag Leipzig 1965, pp. 412-413.
  2. ↑ Walter Wittenberger: Chemical laboratory technology, Springer-Verlag, Vienna, New York, 7th edition, 1973, pp. 105-107, ISBN 3-211-81116-8.