The Classification, Folding, and Use of Filter Paper Sheets

Filter paper sheets are frequently used in lab experiments and HAWACH will talk about the classification, folding, and design of filter paper. Welcome to visit to visit more.

Classification of filter paper sheets

As we know, there are two kinds of filter paper sheets, qualitative, quantitative filter papers, and chromatographic qualitative analysis filter paper. Qualitative filter paper chemistry lab is generally used to filter solutions for qualitative tests that do not require the calculation of values for chlorides, sulfates, etc.; quantitative filter paper is used to filter for precise calculation of values, such as the determination of residues, insoluble, etc. After filtration, there is no need to enter a high-temperature furnace for treatment.

The difference lies in the ash content after ashing. Qualitative filter paper ash content is less than 0.15%, and quantitative filter paper ash content is less than 0.01%.

1. Qualitative filter paper

Qualitative filter paper generally has more residual ash, which is only used for general qualitative analysis and used for filtering precipitation or suspension in solution and cannot be used for quality analysis.

In the manufacturing process, treat the pulp with hydrochloric acid and hydrofluoric acid, and wash it with distilled water in order to remove most of the impurities in the paper fiber, so there is little residual ash after burning, and the analysis results are almost not influenced. It is suitable for precise quantitative analysis.

Usually, the quantitative analysis filter paper is divided into three categories based on the filtering speed: fast, medium, and slow. The filter boxes are classified with white belt (fast), blue belt (medium speed), and red belt (slow speed) respectively. It could be round or square and for the square ones, there are two specifications available, 30cm×30cm and 60cm×60cm. The specifications of the round paper are divided into d9cm, dllcm, d12.5cm, d15cm, and d18cm according to the diameter.

Qualitative and quantitative filter paper is divided into three types: fast, medium, and slow which is divided by the pore size of filter paper sheets.

2. Quantitative analysis filter paper
For the quantitative filter paper, there is little residual ash after burning, which hardly affects the analysis results. It is suitable for precise quantitative analysis. Compared with the quantitative analysis filter paper, the qualitative ones have more residual ash, making them suitable for precipitation or suspension filtration in solution, not for quality analysis. There are filter papers of the fast, medium, and slow speeds available. However, if the quantitative and qualitative analysis filter paper is not described on the packing box, please should pay attention to:
①Natural filtration is generally used, and the filter paper body and the ability to trap solid particles are used to separate the liquid from the solid;
②Due to the small mechanical properties of the filter paper, both the strength and toughness, try to filter by suction as little as possible. To achieve accelerated filtering speed and to prevent filtration failure, two or three layers of filter paper can be stacked in the funnel, based on the suction force, when the air pump is filtered. For filter paper, when vacuum filtration is used, put a layer of dense filter cloth on the funnel, and then put filter paper on it to filter;
③It’s better not to filter nitric acid or sulfuric acid.

filter paper sheets hawach-filter-papers-bio-113

3. Chromatographic qualitative analysis filter paper
Chromatographic qualitative analysis filter paper is mainly used as a support in paper chromatographic analysis to carry out the qualitative separation of the analyte. There are two types of chromatographic qualitative analysis filter paper, and each is divided into fast, medium, and slow speeds.

Fast: the pore size is 80~120 microns
Medium speed: the pore diameter is 30-50 microns
Slow speed: pore diameter is 1~3 microns

The difference lies in the nature of the precipitation of the separated substances, fast filter paper for colloidal precipitation, slow filter paper for crystalline precipitation. Usually, the markings on the packaging box are white, blue, and red.

Folding and usage of filter paper sheets

There are many ways to fold the filter paper. Generally, the four-fold method is used. The main point is to make the folded filter paper fit and close to the inner wall of the funnel. When folding, the hands should be clean, and the cone of the folded filter paper should be consistent with the cone of the funnel used; the folded filter paper sheets have three layers on one half and one layer on the other half. Tear the outer two layers of the three layers.

Remove a small piece and make it fit better with the funnel wall after moistening it with water. The size of the filter paper sheets used should be about one centimeter below the edge of the funnel. Put the filter paper treated in this way into the display hopper, press it tightly by hand to make it tightly, and then use a washing bottle to add a little water to the filter paper to moisten it.

If the folding cone angle is appropriate, there should be no air bubbles between the filter paper and the funnel wall after water is injected, and a water column can be formed in the funnel neck, whereby the gravity of the water column can speed up the filtration speed. If there are bubbles, they should be driven out. The liquid level of the poured filtrate is generally two-thirds of the filter paper sheets. Please keep spare filter paper in the laboratory to prevent moisture or other material contamination.

Use of qualitative filter paper and quantitative filter paper

Why is the filter paper sheets lower than the edge of the funnel?
Filter paper sheets are lower than the edge of the funnel, which is considered from two aspects: one is that the support strength of the filter paper in the immersion state will be further reduced, which is likely to cause liquid spillage; the other is to facilitate the liquid level control in the filtration process.

For filter operation, we should pay attention to “two low”.
1. The edge of the filter paper sheets should be slightly lower than the edge of the funnel by about 5mm;
2. The liquid level in the funnel should be about 5mm lower than the edge of the filter paper sheets. The purpose is to prevent the liquid from flowing into the filtrate from the gap between the filter paper sheets and the inner wall of the funnel.

Operation process of filter paper

1. Fold the filter paper twice in a row to form a 90-degree central angle;
2. Form a funnel by pressing the folded one into 3-layer on one side and opening one layer on the other side;
3. Put it into the funnel. Place the filter paper funnel on the funnel rack for filtering, and place the beaker or test tube under the funnel neck, and the tip of the funnel neck is against the wall of the receiving container;
4. When the liquid to be filtered is injected into the funnel, use your right hand to hold the liquid beaker and hold the glass rod in your left hand. Make the mouth of the cup close to the glass rod. When the filtered liquid flows out along the mouth of the cup, it will flow into the funnel by tilting it along the glass rod. The liquid level of the liquid flowing into the funnel should not exceed the height of the filter paper in the funnel.