There are several types of filter paper depending on the density or number of pores on their surface, as well as their size, which makes them have different properties and applications.
It is used as a physical barrier in laboratories, in order to separate solid or semi-solid substances by the filtration method, which depending on the type of paper used can be fast, intermediate or low speed.
In addition to a mechanical filter barrier, filter paper is also used as an inert support in a variety of qualitative techniques; for example, in electrophoresis and chromatography, to separate and identify organic and inorganic substances.
Filter paper characteristics
The filter paper in its basic structure has cotton fibers made with cellulose, among other materials, presenting the following characteristics:
Filter paper has many holes or pores, as well as different degrees of porosity and different pore sizes. These parameters are relevant when considering their use.
The greater the number of pores and the larger the size, the flow rate or filtration efficiency will vary proportionally. High efficiency is related to high filtration speed.
Term related to the retention of particles during the filtration process. Retained solid particles can clog filter pores that are smaller than particles. The greater the number of pores, the greater the filtration capacity of the filter paper.
By adding some component or chemical stabilizer to the base structure of the filter paper, its hardness or mechanical resistance to humidity is improved. The higher the hardness, the higher the quality and the less deformation or deterioration of the paper.
It will also have a higher volumetric flow rate and better efficiency, being optimal for use in procedures under high pressure and vacuum conditions.
Applicability or inert support
The filter paper constitutes an inert support, it is resistant to the variety of chemical reactions that can be carried out in it, and also does not generate impurities.
There are specific controls in the production of filter paper so that it can be used in special tests, such as reducing the percentage of ash, or so that it can be used in measurements of ash from the waste.
In other controls, for example, the presence of nitrogen on the paper is restricted for use in blood nitrogen measurements.
Filter paper is used in laboratories during the performance of different filtration, precipitation, and qualitative analysis techniques. It also has application in procedures that require high precision or quantitative analysis.
The filter paper has the function of separating molecules or solid substances present in a liquid or in the air that is passed through its surface.
For this process, qualitative paper is used.
The porosity of paper allows fluids or liquid particles to pass through it, without allowing solid particles or substances to pass through.
The absorption properties of filter paper are important: absorption of water in filtering processes, or absorption of reagents, as happens in qualitative test strips, used in urinalysis, in pH indicators, among others.
On the contrary, when it is used in the electrophoresis technique, the less absorbent the paper, the better the results will be obtained.
Only quantitative filter paper can be used for quality analysis or quantitative determinations, which require high precision.
Filter paper types
There are several types of filter paper. They can be classified taking into account different criteria such as the manufacturing material, the use that will be given to it, the manufacturer, among other aspects.
– According to the manufacturing material
Depending on the manufacturing material, the paper can be made of cellulose, glass microfiber, etc.
– According to its use
Qualitative filter paper is mainly made of cellulose. It generally contains more residual ash, and is widely used to filter solutions.
This paper is used in chemical determinations of a qualitative nature, or to analyze the colors of substances by separating them by paper chromatography.
Qualitative filter paper is in turn classified into three types: standard paper, paper with greater resistance to humidity, and qualitative paper for chromatography. Each one having different grades or even more classifications according to the provider.
Quantitative filter paper has low impurities and ash. This role also has several subtypes. It is used in filtrates that require quantitative analysis processes, such as residual value determinations and quantification of unfiltered substances.
– According to the manufacturer
Filter paper is named after the manufacturer. For example, there is the Whatman paper, which in turn is classified into different grades or numbers. There is also Hawach Scientific paper, which in turn has its own specifications.
Examples of filter paper use
Removal of substances in liquids
A daily use is to use the qualitative filter paper, moisture resistant grade, to carry out filtration or clarification processes of solutions. Various types of solutions are filtered, oily substances such as oils, to clarify beverages, medicines, among others.
The filter paper serves as a support or stationary phase medium to carry out the separation of ions, proteins or other substances, by the electrophoresis technique.
Another method of separation and identification of substances that filter paper uses is chromatography. In the thin-layer chromatography variety, filter paper serves as the stationary, solid, and inert phase.
Filter paper is used to determine the ash weight of unfiltered residues or compounds.
As mentioned, there are many uses for filter paper, even the least porous ones are used to weigh solid substances