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Grade classification

Pure gases are classified by grade.

GradeMinimum purityTotal impurities
N2.099%1%
N3.099.9%1000ppm
N4.099.99%100vpm
N5.099.999%10vpm
N6.099.99991vpm
N7.099.99999%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

PercentParts per millionParts per billion
1%10,000ppm-
0.1%1000ppm-
0.01%100ppm-
0.001%10ppm10,000ppb
0.0001%11000ppb
-0.1ppm100ppb
-0.01ppm10ppb

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