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  • Purity, Grades and Concentration

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

Related Links
  • Pure Gases
  • High purity mixtures

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