Purity, grades and concentration
Grade classification
Pure gases are classified by grade.
Grade | Minimum purity | Total impurities |
|---|---|---|
N2.0 | 99% | 1% |
N3.0 | 99.9% | 1000ppm |
N4.0 | 99.99% | 100vpm |
N5.0 | 99.999% | 10vpm |
N6.0 | 99.9999% | 1vpm |
N7.0 | 99.99999% | 100vpb |
The first digit of the grade classification indicates the 'number of nines' purity, e.g. N3.0 = 99.9% purity.
The second digit is the number following the last nine, e.g. N4.6 helium has a guaranteed minimum purity level of 99.996%.
Concentration conversion table
Percent | Parts per million | Parts per billion |
|---|---|---|
1% | 10,000ppm | - |
0.1% | 1000ppm | - |
0.01% | 100ppm | - |
0.001% | 10ppm | 10,000ppb |
0.0001% | 1 | 1000ppb |
- | 0.1ppm | 100ppb |
- | 0.01ppm | 10ppb |