Cylinder fillings frequently display purities that are higher than those which have been guaranteed. Even if this should occur repeatedly, it should nevertheless not be taken as any assurance of uniformly higher purities. The maybe simpliest and most accurate definition of purity is:
“Purity is the absence of impurity in a substance”
Impurity can be defined as a material or substance in the finished product that differs from the chemical composition of the requested material or compound. BUT: 100% purity cannot be achieved due to the manufacturing process.
Purity classification is normally written in two ways:
1. As a quality code, e.g. 5.5 where the number before the dot represents the number of nines and the last number indicates the last decimal (5.5 = 99,9995% or 6.0 = 99,9999%)
2. As impurity in percent, e.g. >99,9995.
Ethylene 2.8 means 99.8 % purity
Argon 6.0 means 99.9999 % purity
Reported impurity level as %
Reported impurity level as ppm
|99,0%||2.0||1%||10 000 ppm|
|99,5%||2.5||0,5%||5 000 ppm|
|99,9%||3.0||0,1%||1 000 ppm|
|99,9999%||6.0||0,0001%||1 ppm (1000ppb)|
Instead of the short suffix, a few gases have an application-related suffix, e.g. Nitrogen CO-free. Irrespective of the minimum purity indicated in the product description, these gases have an especially low residual content of certain otherwise troublesome impurities.