4 Aspects to Be Considered When Choosing Filter Paper and How to Use It

Chemical analysis filter paper (qualitative filter paper, quantitative filter paper ) is made of high-quality high-grade cotton, using modern and unique papermaking technology and advanced papermaking equipment. It is a kind of high purity, uniform organization, and has a certain filtering speed and a certain strength of cotton paper. They are widely used in scientific research, industry, agriculture, medicine and health, environmental protection, and other departments for qualitative and quantitative layer analysis and testing. Here are four points to be considered when selecting filter paper.

The choice of filter paper should be determined according to the requirements of the analysis work for filtration and precipitation and the nature and quantity of the precipitation. There are two types of filter papers available in HAWACH. The difference between quantitative filter paper and qualitative filter paper is mainly in the amount of ash produced after ashing: qualitative filter paper does not exceed 0.13%, and quantitative filter paper does not exceed 0.0009%. they can be used in different experiments. According to the size of pores, both quantitative and qualitative filter paper can be divided into three types: fast, medium, and slow. Fast filter paper has large pores, while slow filter paper has small pores.

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: spots are not easy to spread, suitable for samples with small Rf value and developing agents with low viscosity, but the developing time is long;
3. The medium-speed filter paper is between the two.

4 aspects when selecting filter paper

The composition of most filter paper disc is cotton fiber, and there are countless small holes on the surface for liquid ions to pass through, while larger solids cannot pass. This property can satisfy the separation of liquid and solid substances mixed together. Different filter papers have different functions and characteristics, which can meet the filtration problems of a variety of solutions. Users need to pay attention to four aspects when selecting filter paper types. These four points are hardness, filtration efficiency, capacity, and applicability.

Hardness: Quantitative filter paper will become wet during filtration. Consider the tougher filter paper after wet water if for long-term filtration experiments. Qualitative filter paper generally has high adsorption capacity, smooth surface, high wet strength, and a wide application range.

Filtration efficiency: The density and size of the pores on the quantitative filter paper affect its filtration efficiency. High-efficiency filter paper has both fast speed and high resolution. The finished qualitative filter paper has a relatively flat surface, uniform texture, high resolution, good results reproducibility, strong load capacity, good diffusion effect, very few impurities, and low background interference.

Capacity: The solid particles accumulated during filtration or the pores on the filter paper are blocked. Therefore, the denser the water seepage pores, the higher its capacity represents, and the more filter lines are allowed to be filtered.

Applicability: In addition to the normal filter papers, some are made by special processing steps. For example, when used in laboratory medicine to determine the nitrogen content in the blood, nitrogen-free filter paper must be used.

How to use filter paper

In experiments, filter paper is often used together with equipment such as filter funnels and Buchner funnels. Before use, it needs to be folded and a flower-like shape is commonly used. The higher the folding degree of the filter paper, the higher the surface area it can provide and the better the filtering effect, but be careful not to over-fold the filter paper and cause the filter paper to break. Put the drained glass rod on the multi-layer filter paper and apply it evenly to avoid damage to the filter paper. Here are the operation processes.

The filter paper is usually used with the funnel and a flower-shaped folding method is frequently used.
1. Fold the filter paper twice in a row to form a funnel with a 90° central angle.
2. Form a funnel by pressing one side of folded filter paper into three layers and one side one layer.
3. Pour some clean water into the mouth of the funnel to make the soaked filter paper stick to the inner wall of the funnel, and then pour out the remaining clean water and set it aside.
4. Place the funnel with the filter paper on the funnel stand for filtering (such as the ring of the iron stand), place the beaker or test tube that receives the filtrate under the neck of the funnel, and make the tip of the neck of the funnel rest against the surface of the receiving container, and make the tip lean against the wall.

5. When pouring the liquid to be filtered into the funnel, hold the liquid beaker in the right hand and the glass rod in the left. Make the glass rod’s lower end is close to the three-layer funnel lower side, to ensure the cup mouth is close to the glass rod until the filtrate body flows out along the cup mouth, and then along the slope of the glass rod, it flows into the funnel, and the liquid flowing into the funnel cannot exceed the height of the filter paper in the funnel.

6. When the liquid flows down the funnel neck through the filter paper, check whether the liquid flows down the wall of the cup and pours to the bottom of the cup. Otherwise, the beaker should be moved or the funnel should be rotated so that the tip of the funnel is firmly attached to the wall of the beaker so that the liquid can flow down slowly along the inner wall of the beaker.