are divided into two series, qualitative filter paper, and quantitative filter paper. Qualitative filter papers are divided into standard grades and wet strengthened grades. Wet strengthened grades are added a small amount of chemical stabilizer on the basis of the standard grades. Quantitative filter paper is generally aimed at ashless filter paper. It must undergo special treatment procedures during use. To a certain extent, it can effectively resist certain chemical reactions, so impurities generated on its surface will be much less, under normal circumstances it is generally used in quantitative analysis.