Filter paper is a kind of paper with good filtration performance. The paper is loose and has strong absorption for liquid. Filter paper is often used as the filter medium in the analysis laboratory to separate the solution from the solid. At present, there are three kinds of filter paper produced in China: quantitative analysis filter paper, qualitative analysis filter paper and chromatography qualitative analysis filter paper. Quantitative filter paper and qualitative filter paper are two concepts of cellulose filter paper, which are not suitable for other types of filter paper such as glass microfiber filter paper. Qualitative filter paper is used for qualitative chemical analysis and corresponding filtration separation. Qualitative filter paper is generally used to filter solution, do qualitative test of chloride, sulfate, etc. without calculation value; while quantitative filter paper is used to filter precise calculation value, such as determination of residue, insoluble matter, etc. generally, after quantitative filter paper is filtered, it needs to enter high temperature furnace for treatment.
1. Quantitative analysis filter paper quantitative analysis in the manufacturing process of filter paper, the paper pulp is treated with hydrochloric acid and hydrofluoric acid, washed with distilled water, and most impurities in the paper fiber are removed, so there is little residual ash after burning, which has little impact on the analysis results, so it is suitable for precise quantitative analysis. At present, the quantitative analysis filter paper produced in China is divided into three categories: fast, medium speed and slow speed. The white band (fast), blue band (medium speed) and red band (slow speed) are used as the mark classification on the filter box. The shape of filter paper has two kinds: round and square. According to the diameter, the specifications of circular fixed paper can be divided into d9cm, dllcm, d12.5cm, d15cm and d18cm. There are 60cm × 60cm and 30cm × 30cm square quantitative filter paper.
2. Qualitative analysis filter paper qualitative analysis filter paper generally has a large amount of residual ash, which is only used for general qualitative analysis and suspension in filtration precipitation or solution, not for quality analysis. The type and specification of qualitative analysis filter paper are basically the same as that of quantitative analysis filter paper, indicating fast, medium speed and slow speed, but printing the words of fast, medium speed and slow speed. However, it is not stated on the box of filter paper that when using quantitative and qualitative analysis filter paper to filter sediment, attention should be paid to:
① Generally, natural filtration is adopted, and the ability of filter paper body and solid particle interception is used to separate liquid and solid;
② Due to the small mechanical strength and toughness of filter paper, the method of suction filtration should be minimized. If the filtration speed must be accelerated, in order to prevent filtration failure due to filtration through, two or three layers of filter paper can be stacked in the funnel according to the suction force. When vacuum filtration is used, a layer of dense filter cloth should be placed in the funnel first, and then filter paper should be placed on the funnel for filtration;
③ Filter paper is better not to filter hot concentrated sulfuric acid or nitric acid solution;
3. Chromatography qualitative analysis filter paper chromatography qualitative analysis filter paper is mainly used as a support in paper chromatography. There are two kinds of qualitative separation chromatography qualitative analysis filter paper No.1 and No.3 for the substance to be tested, each of which is divided into three kinds: fast, medium and slow. In addition, the difference between quantitative filter paper and qualitative filter paper is that qualitative filter paper is used for qualitative chemical analysis and corresponding filtration separation; quantitative filter paper is used for gravimetric analysis test and corresponding analysis test in quantitative chemical analysis. The function of quantitative filter paper is mainly used for the ashing weighing analysis experiment after filtration. The ash weight of each filter paper after ashing is a fixed value, while the qualitative filter paper is used for general filtration. The difference between quantitative filter paper and qualitative filter paper mainly lies in the amount of ash produced after ashing. Qualitative filter paper shall not exceed 0.13% and quantitative filter paper shall not exceed 0.0009%. Ash free filter paper is a kind of quantitative filter paper, its ash content is less than 0.1mg, and this weight can be ignored in analytical balance. Note that the two concepts of quantitative filter paper and qualitative filter paper are unique to cellulose filter paper, and they are not applicable to other types of filter paper such as glass microfiber filter paper.
