How is the purity of the oxygen generator product expressed?

In the process of production, indicators such as the purity of oxygen products is not less than 99.5%, the purity of nitrogen is not less than 99.99%, and the purity of argon is not less than 99.999% will be encountered. These indicators indicate the content of main substances in the product. Because it is very difficult for the product to achieve absolute purity, more or less there are some impurities, therefore, the degree of its purity is called purity. There are two ways to express the content of certain substance in the gas mixture, one is called mass fraction; the other is called volume fraction. Mass fraction refers to the percentage of the mass of a certain component in the total mass of the mixture; volume fraction refers to the percentage of the volume of a certain component in the total volume of the mixture. For the same content, the values of the two scores are different. For example, the volume fraction of oxygen in the air is 20.93%, while the mass fraction is 23.1%.
Gas mixture is mixed evenly by gas. They have the same temperature and fill the whole space. The volume occupied by each gas in the volume fraction refers to the volume occupied respectively when various components of the mixed gas are separated and the original temperature and pressure are maintained. As shown in figure 5, at this time, the volume occupied by various gases is called Volume: V1, V2, etc. The sum of separate volumes is equal to the original total Volume V. Volume fraction is the ratio of volume to total volume. The purity of gas products generally refers to the volume fraction.