This International Standard defines the following quantities commonly used to express the composition of gas mixtures:. mole fraction,. mass fraction,. volume fraction, and . mole concentration,. mass concentration,. volume concentration.For these quantities of composition, this International Standard provides methods for. conversion between different quantities, and. conversion between different state conditions.Conversion between different quantities means calculating the numerical value of an analyte content in terms of one of the quantities listed above from the numerical value of the same analyte content, at the same pressure and temperature of the gas