What are the codes for various high-purity gases? There are usually two types of gas purity indicators

For chemists, purity levels such as 99%, 99.9%, 99.99%, 99.999%, 99.9999%, 99.999999%, and 99.999999% are generally used. So the remaining 1%, 0.1%, 0.01%, 0.001%, 0.0001%, 0.00001%, and 0.000001% are impurities.

Physicists use a simple method of n "9" statements based on the above mentioned "9" statements. The purities mentioned above can be written as 2N, 3N, 4N, 5N, 6N, 7N, 8N respectively. If written as 4N8 or 5N5, the purities are 99.998% and 99.9995%, respectively; If written as 5N85, the purity is 99.99985%.

There are constant, trace, and trace representations for impurity content, and for impurities below trace and trace levels, they generally refer to the range of ppm to ppb. The specific impurity concentration is: lppm=10-4％;  1ppb=10-7％;  1ppt=10-10%.

Classification of impurities in gases: Impurities in gases are classified by chemical properties into oxidizing gases (such as oxygen, carbon dioxide, water), reducing gases (such as hydrogen, carbon monoxide), and inert gases (such as nitrogen, argon, helium). If impurities are classified by form, they include gaseous impurities (such as oxygen, nitrogen, carbon monoxide, carbon dioxide, methane, hydrogen), liquid gas impurities (such as water), and solid gas impurities (such as particles or dust).