Systems and methods are disclosed for calibrating mass spectrometers. In accordance with one implementation, a system comprises a calibrant chamber within a housing of a mass spectrometer. The system also comprises a permeation tube enclosed within the calibrant chamber, wherein the tube contains a calibrant chemical that continuously outgasses the calibrant chemical. The outgassed calibrant chemical may be introduced to the mass spectrometer for analysis. The system may also comprise a heating block to control the temperature of the calibrant chemical. The system may further comprise a valve that introduces a known amount of the calibrant chemical into the calibrant chamber. In accordance with the present disclosure, systems and methods are provided for calibrating a mass spectrometer abundance scale.