About Applications and Less Frequently Uses of the Qualitative Filter Paper

For experiment operators, filter paper is one of the most frequently used tools in the lab and it has many applications. Today HAWACH has summarized not only the common usages but also various fewer uses of qualitative filter paper.

Filter paper working principle

Filter paper filtration is actually chromatography, and paper chromatography uses filter paper as an inert support. The filter paper fiber has a strong affinity with water and can absorb nearly one-fourth of the water, and part of the water is combined with the hydroxyl group of cellulose in the form of hydrogen bonds, which is difficult to remove under normal conditions. The affinity of filter paper fibers with organic solvents is weak, so general filter paper chromatography actually uses the bound water of filter paper fibers as the stationary phase and organic solvents as the mobile phase.

When the mobile phase passes through the sample along with the paper, the solute on the sample is continuously distributed between the water and the organic phase. A portion of the sample moves with the mobile phase into the solute-free region, where it is redistributed, and a portion of the solute moves from the mobile phase into the stationary phase (aqueous phase). With the continuous movement of the mobile phase, various parts are continuously distributed according to their respective distribution coefficients, and move along the mobile phase, so that the substances can be separated and purified.

hawach-filter-papers-bio-41 filter paper for laboratory use quantitative-filter-papers-bio-41

There are several main considerations in the selection of filter paper:

1. Effective area: the larger, the better.
2. Fiber diameter: the smaller, the better.
3. Binder content in the filter material: the higher, the better.

Qualitative filter paper
The qualitative filter paper filtration belongs to natural filtration, taking the filter paper itself ability to trap the solid particles and achieve separation between the liquid and solid. But please note the suction filtration is not suggested to use frequently, because of its mechanical strength and toughness. If it is necessary to speed up the filtration rate, in order to prevent the filtration failure caused by the filtration, during the air pump filtration, double or multilayer filter paper can be used based on the suction force. Place a layer of dense filter cloth first if for vacuum filtration. Please note the filter paper is not suitable for acid solution filtration.

Various applications of qualitative filter paper

  1. Particulate Filtration:
    • The primary and most common use of qualitative filter paper is for the separation of solid particles from liquids. It is used to remove impurities, precipitates, or undissolved materials from a liquid sample.
  2. Qualitative Analysis:
    • As the name suggests, qualitative filter paper is often used in qualitative analysis techniques, where the goal is to identify the presence or absence of specific substances in a sample.
  3. Microbiological Testing:
    • In microbiology, qualitative filter paper can be used for filtering microbial cultures to separate cells or other solid components from liquid media.
  4. Sample Clarification:
    • It is used to clarify turbid or cloudy liquids by removing suspended particles. This is common in environmental water analysis and industrial applications.
  5. Desalting and Buffer Exchange:
    • Qualitative filter paper can be used in desalting and buffer exchange procedures to remove salts or change the buffer composition of a sample.

Qualitative filter paper is the most commonly used in conventional filtration, with various flow rates and different separation capabilities. In general, the slower the filtration rate, the stronger the separation ability, the better the adsorption effect. For industrial filter paper, you can choose medium-speed filter paper, which saves time while ensuring filtration performance. Medium flow rate and medium particle retention can filter high-viscosity liquids and emulsions (such as sweet juice, wine, syrup, resin solution, oil or plant extracts, Chinese medicine soaking liquid). The quick filter paper is slightly thicker than that, has a higher load capacity, and is suitable for coarse particles, medium and colloidal sediments. Ashless filter paper covers most of the scope of laboratory applications, often used for clarification of liquids, and also used for qualitative analysis and separation of sediments.

What’s more, the qualitative filter paper can be used for the separation of solid substances from liquids or liquid extraction. It is not used as an analysis filter paper, but as a paper filter material. It is used as paper filter material, from coarse filtration of western medicine liquid, coarse filtration and fine filtration of Chinese patent medicine, to filtration of chemical products, filtration of electroplating industry, etc. This filter paper is also often used in daily analysis applications in different industries.

hawach-filter-papers-grade-4  qualitative-filter-paper-roll-grade-2 20-micron-filter-paper-bio-4

Less frequently uses of the qualitative filter paper

HAWACH is specializing in the production of qualitative filter papers, with a variety of diameters ¢7cm, ¢9cm, ¢11cm, ¢12.5cm, ¢15cm, ¢18cm, ¢22cm. According to the separation performance, it is divided into slow, medium, and fast speeds. Of course, in addition to filtration, it has other usages which you may don’t know. This time, HAWACH has collected the following 13 different usages of the qualitative filter paper.

1. Atomic absorption burner has been used for a long time and there will be carbon deposits. Generally speaking, qualitative filter paper will be selected for cleaning if it is not too serious. Unless it is too difficult to clean, use a knife to gently scrape the carbon deposits.

2. When using the pH timer, the glass electrode must be rinsed with deionized water continuously during the interval of the use process, but there will be deionized water on the electrode after the rinse, if it is directly put into the sample to be tested, it will interfere with the sample to be tested. Now, you can use filter paper to gently soak up the water on the electrode. Please note that do not touch the middle glass ball frequently.

3. Carbon tetrachloride in the analysis oil project needs to be adsorbed by activated carbon before it is used, but carbon tetrachloride is particularly volatile. Sometimes it can lose one-fifth of a bottle in 20 minutes, and there is no matching adsorption column cover, so we suggest put filter paper on the adsorption column top and use a rubber band to fix it. We suggest using three pieces of filter paper to seal the lid. The effect is good, and carbon tetrachloride volatilizes very little.
4. A filter paper with a few holes put on the mouth of the beaker, a dehumidifier is produced.
5. The biggest advantage of filter paper is that it has very good water absorption, so sometimes burette or separatory funnel, we will choose to use filter paper to absorb excess reagents.
6. Wipe the excess reagent on the cuvette.
7. When doing titration, use filter paper to compare the titration color.
8. Filter paper can also be used for another purpose. We need to remove the icing when testing sugar-coated tablets. We can moisten the icing layer with water and rub the icing off. Then use filter paper to absorb the outside water, and finally put it into a desiccator to dry. We succeed in manufacturing plain film.
9. When drying some reagents that do not need to be weighed, the filter paper can be dried better. After drying, the filter paper’s color will change and also become brittle.
10. It can be taken as a biological indicator carrier. This is very good for the high-pressure steam sterilization indicator used in general laboratories.
11. It is also used when making fat. Fold the filter paper and put it in the Soxhlet extractor.
12. When we need to filter liquid samples, generally, we use the kind of filter tip that you bought. If there is no filter tip temporarily, and you want to filter, it is also a good idea to squeeze the filter paper into a small ball and plug it into the syringe. It will become a smple and cheap filter device.
13. Use as recording paper.
In our daily analysis process, we will encounter the use of filter paper frequently. Do you have any other uses about qualitative filter paper? Welcome to share it with us.