Chemical ionization mass spectrometry: A method of estimating reagent gas pressure in the ion source based on kinetic data

Consequential upon determinations of kinetic rate constants of ion/molecule reactions in methane and isobutane, simple equations are presented from which the pressures of methane and isobutane in the ion source of chemical ionization mass spectrometers can be calculated. Account is taken of the design of the ion source and it is only necessary to determine two ion currents for each gas.