The purity required will be a function of the end use application. There are a variety of grades of hydrogen that can be purchased. The H2 purity will also vary based on source (GH2 or LH2) and production method. CGA G-5.3, Commodity Specification for Hydrogen, lists several typical purities of both liquid and gaseous hydrogen. Standard GH2 available from most suppliers is 99.95% hydrogen. Standard LH2 standard purity is 99.995 % by volume. Often the hydrogen is purer than stated, but the stated purity is based upon the level of analysis. For example, LH2 is usually at least 99.998% pure. Standard quality testing usually includes a “total purity” measurement as well as for typical impurities such as H2O, O2, CO, CO2, and hydrocarbons. Fuel cell applications usually are required to meet the SAE J2719 or ISO 14687 specifications for PEM fuel cell. These specifications list the minimum requirements for over a dozen impurities.