What Is the Quality Inspection Method of Quantitative Ashless Filter Paper?

Filtration is the technique that is widely used to separate solids from liquids in the modern lab, by the casting of pouring a mixture onto a membrane, such as filter paper, allowing the liquid to go past and get the results with the collection of the solid parts.

In the process of filtration, the retention level is determined by many factors, such as the retention on the surface and the retention depth. The effects of inertia, electrostatic adsorption, and sedimentation can also work on retention as well. With filter papers which is simple to look at, and easy to use, the goal of filtration is to achieve the fastest velocity for the required retention level.

Looking back into the history of filter papers, we can find J.J. Berzelius (1779–1848), a Swedish chemist who invented the first real filter paper in the world. J.J. Berzelius was also the first chemist who completed the retention of precipitates by using pure wet-laid all-rag paper during the chemical analysis.

With Berzelius’s help, the filter papers began to be manufactured at the paper mill in Sweden around the year 1815. After few years, similar products could be found in other European countries. Since then, the development pattern for the filter paper became clear.

Quantitative filter paper

The pulp of quantitative filter paper is made after leaching with hydrochloric acid and hydrofluoric acid. The content of iron, aluminum, silicon, etc. in the paper is very low. The ash weight of filter paper after burning is less than 0.01 mg/sheet. The filtration speed of quantitative filter paper is divided into three types: fast, medium, and slow, which are marked on the filter carton with different colored paper tapes. The pore size of 80～120 microns is fast quantitative filter paper, 1～3 microns slow speed and 30-50 microns belong to medium speed.

Ashless filter paper

Ashless filter paper (quantitative analysis filter paper) is a kind of quantitative filter paper. After the quantitative filter paper is burned, the filter paper with an ash content of less than 0.0001g becomes an ashless filter paper, suitable for quantitative analysis in chemical analysis. The basis weight is 80g/m2. According to different filtration speeds, it can also be divided into different specifications of fast, medium, and slow speed.

Quality inspection

Quality inspection method of quantitative ashless filter paper is as follows:

Ash test: Accurately weigh 10 pieces of ashless filter paper, take two of them torn into pieces, and places them in two accurately weighed platinum crucibles, and heat them with warm fire in a high-temperature furnace, and then add high temperature. After cooling, the crucible is cooled to room temperature in a desiccator and weighed. The average weight of the ash content of each filter paper can be obtained by subtraction.

Barium sulfate retention test: Heat 20 ml of sulfuric acid to boiling, slowly drip 20 ml of barium chloride solution with a certain equivalent concentration at a rate of 1 ml/sec and continue heating after dripping. After 30 seconds, filter the mixture with filter paper and observe whether the filtrate has white precipitates, which indicates whether the filter paper can retain barium sulfoate.

Starch test: If starch is present in the starch test filter paper, it cannot be used for carbohydrate analysis. The method to test the presence or absence of starch in the filter paper is: tear the filter paper, azeotrope it with distilled water, and drop it into 0.01N dilute iodine solution. If it appears blue, it means that there is starch.

Test of iron in filter paper: Add a drop of paper ammonium solution on the filter paper, and then add a drop of hydrochloric acid. If there is no iron, there will be no brown spots.