Topics - Argon
Argon is an inert, monatomic gas, having an atomic weight of 40. In gas chromatography, argon must be used as the mobile phase, when the argon detector is employed, and as a mixture with methane, when the electron capture detector is employed. As an inert gas, collisions between argon atoms and electrons are perfectly elastic. Thus, if electrons are generated in argon and are then accelerated under a suitable potential, despite collisions, the velocity (and, thus, the energy) of the electrons continually increase. However, when the energy of an electron reaches 11.6 electron volts or more, on collision with an argon atom, energy is adsorbed and one of its electrons changes orbit and a metastable argon atom is formed. This metastable argon atom, having an energy of 11.6 electron volts, will ionize virtually all organic molecules producing ion and electron pairs. These pairs can be collected by suitably placed electrodes under an appropriate voltage gradient and used as a sensing process for GC detection. The argon detector, functioning in this manner has been shown to have an ionization efficiency of 0.5 % (cf. 0.0015% for the flame ionization detector) and a sensitivity of about 3 x 10-13 g/ml (solute n-heptane). The argon detector is one of the most sensitive general detectors.