Mass spectrometric analysis of high-purity helium and hydrogen, using a dynamic sampling and calibration system

A dynamic gas sampling system has been designed for use with a mass spectrometer (A.E.I. Model MS2G). It is capable of sampling directly from gas streams at pressures in the region of 800 torr and has been satisfactorily used for the analysis of high-purity helium and hydrogen containing less than 50 vpm total impurity. The overall sensitivity is 1 vpm or better. The design permits the mass spectrometer to be used with its normal gas sampling system when required. A dynamic gas blending rig, incorporating a recirculation and purification system, has been developed for the calibration of the mass spectrometer over the range 5-100 vpm of impurity content.