What Are the Precautions Should Be Taken Using Filter Paper?

Filter paper classification

Filter paper can be divided into qualitative and quantitative filter papers. The function quantitative filter paper is mainly used for washing and weighing analysis experiments after filtration. According to the size of the pores, filter paper can be divided into three types: fast, medium, and slow. The fast filter paper has the largest pores, and the slow filter paper has the smallest pores. Such as Hawach Qualitative 20 Micron Filter Paper Grade: BIO-4 is fast pores, Qualitative Filter Paper Disc Grade: BIO-1, Qualitative Laboratory Filtration Filter Paper Grade: BIO-2 are medium pores, Qualitative Chromatography Filter Paper Grade: BIO-5, Qualitative Filter Paper Biology Grade: BIO-6 are slow pores for your choice.

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1. Fast filter paper, because the paper is loose and the spots are easy to spread, it is suitable for samples with large Rf values and developing agents with large viscosity.
2. Slow filter paper, the spots are not easy to spread, suitable for samples with small Rf values and developing agents with low viscosity, but the developing time is longer.
3. Medium-speed filter paper is between the two.

If there is no instruction on the filter paper packaging box to use quantitative and qualitative analysis filter paper to filter the precipitate, the following matters should be paid attention to:
a. Adopt natural filtration and separate liquids and solids by utilizing the filter paper body and its ability to retain solid particles;
b. It’s better not to use suction filtration, due to the small toughness and mechanical strength of the filter paper. If the filtration speed must be accelerated, it can be stacked in the funnel according to the suction force, when the air pump is filtration, in order to prevent filtration failure caused by filtration.
c. Please note that nitric or sulfuric acid is not suggested to use filter paper to filter.

What should we note when filtering?

For the convenience of memory, the essentials in the filtering operation can be summarized as one angle, two stirrings, three standing, four lower, and five contacts.

1. Angle: It means that the angle of the filter paper when folded should be consistent with the angle of the funnel. The filter paper cut in this way can stick to the inner wall of the funnel, so as to ensure a fast filtration rate.

2. Stirring: After pouring the mixture into water, stirring with a glass rod can speed up the dissolution rate of soluble substances in it.

3. Standstill: After the soluble substances are completely dissolved, do not filter immediately, but stand for a while. The purpose is to precipitate a part of the particles of insoluble substances first, which can reduce or prevent the insoluble substances from clogging the tiny pores on the filter paper, thereby speeding up the rate of filtration.

4. To be lower: It means that the edge of the filter paper is slightly lower than the edge of the funnel; during the entire filtration process, it is also necessary to always notice that the liquid level of the filtrate is lower than the edge of the filter paper. Otherwise, the filtered liquid will flow down from the gap between the filter paper and the funnel, and flow directly into the receiver under the funnel, so that the unfiltered liquid will be mixed with the filtrate, making the filtrate turbid and failing to achieve the purpose of filtration.

5. Contact: When the liquid is poured into the funnel, the beaker mouth of the beaker containing the liquid to be filtered should be in contact with the inclined glass rod. Also, it means that the lower end of the glass rod should be in contact with the three-layered side of the filter paper. The third means that the neck of the funnel should be in contact with the inner wall of the receptacle that receives the filtrate.