Editing Filter paper (section)

==Laboratory-grade paper filters==
{{See also|Filtration}}
[[File:Filter paper 840 3x3 copy.jpg#file|thumb|left|A scan of Whatman Filter Paper 4 Qualitative taken at 840 magnifications under a [[scanning electron microscope]].]]

Filter papers are widely used in laboratory experiments across many different fields, from biology to chemistry. The type of filter used will differ according to the purpose of the procedure and the chemicals involved. Generally, filter papers are used with laboratory techniques such as gravity or vacuum filtration.<ref name="UCI_2013"/>

Historically, a type of soft, porous paper called ''charta emporetica'' was used in [[pharmacy]] as a filter and as packing paper.<ref name="Cyclopaedia"/>

=== Qualitative filter paper ===
Qualitative filter paper is used in qualitative analytical techniques to determine materials. There are different grades of qualitative filter paper according to different pore size. There are total 13 different grades of qualitative filter paper. The largest pore size is grade&nbsp;4; the smallest pore size is grade 602&nbsp;h; the most commonly used grades are grade&nbsp;1 to grade 4.<ref name="qualitative"/>
[[File:Whatman filter paper.jpg|thumb|150mm qualitative filter paper]]
Grade&nbsp;1 qualitative filter paper has the pore size of 11&nbsp;μm. This grade of filter paper is widely used for many different fields in agricultural analysis, [[air pollution]] monitoring and other similar experiments.<ref name="qualitative"/>

Grade&nbsp;2 qualitative filter paper has the pore size of 8&nbsp;μm. This grade of filter paper requires more filtration time than Grade&nbsp;1 filter paper. This filter paper is used for monitoring specific contaminants in the atmosphere and soil testing.<ref name="qualitative"/>

Grade&nbsp;3 qualitative filter paper has the pore size of 6&nbsp;μm. This grade of filter paper is very suitable for carrying samples after filtration.<ref name="qualitative"/>

Grade&nbsp;4 qualitative filter paper has the pore size of 20~25&nbsp;μm. This grade of filter paper has the largest pore size among all standard qualitative filter papers. It is very useful as rapid filter for cleanup of geological fluids or organic extracts during experiment.<ref name="qualitative"/>

Grade 602&nbsp;h qualitative filter paper has the pore size of 2&nbsp;μm. This grade of filter paper has the smallest pore size among all standard qualitative filter papers. It is used for collecting or removing fine particles.<ref name="qualitative"/>

=== Quantitative filter paper ===
Quantitative filter paper, also called ash-free filter paper, is used for quantitative and gravimetric analysis. During the manufacturing, producers use acid to make the paper ash-less and achieve high purity.<ref name="Fisher"/><ref name="Papers"/>
[[File:Chromatography paper.jpg|thumb|filter paper uses for paper chromatography]]

=== Chromatography papers ===
Chromatography is a method chemists use to separate compounds. This type of filter paper has specific water flow rate and absorption speed to maximize the result of paper chromatography. The absorption speed of this type of filter paper is from 6&nbsp;cm to 18&nbsp;cm and the thickness is from 0.17&nbsp;mm from 0.93&nbsp;mm.<ref name="Labtek"/>

=== Extraction thimbles ===
Extraction thimbles are rod-shape filter paper often used in [[soxhlet extractor]]s or atomized extractors. It is ideal for very sensitive detection, the performance depends on the thickness of inner diameter. Also, it is usually used in areas of food control and environmental monitoring.<ref name="Thimbles"/>

=== Glass fiber filters ===
Glass fiber filter has the pore size of 1&nbsp;μm, it is useful for filtering highly contaminated solutions or difficult-to-filter solution. Also, glass fiber filter has extends filter life, wide range of particulate loads and can prevent sample contamination.<ref name="Pall"/> In addition, different types of glass fiber filter are suitable for different filtration situation. There are 7 different types of glass fiber filters and the major difference is thickness.

=== Quartz fiber filter ===
Quartz fiber filter paper has a high resistance to chemicals, does not absorb NO<sub>x</sub> and SO<sub>x</sub> dioxides, is unaffected by humidity and is easily sterilized. Thus, it is mostly used for air pollution analysis.<ref name="quartz"/>

=== PTFE filter ===
[[Polytetrafluoroethylene]] (PTFE) filter has wide operating temperature (−120&nbsp;°C&nbsp;~ 260&nbsp;°C) with high [[air permeability]]. The resistance to high temperature makes PTFE filter paper suitable for use in autoclaves. It is often used to filter hot oils, strong solvents and collecting airborne particulates.<ref name="quartz"/>