A system has been constructed for the quantitative measurement of low-impurity levels in rare gases at both above and below atmospheric pressure. This system, based on a gas chromatograph with metastable helium detectors, allows measurements to be made down to some tens of ppb impurity levels of all active gases, with good reproducibility. The technique has been used to determine the properties of a new type of single-stage rare gas purifier whose working principle is the chemical sorption of the active gases by means of a gettering material held at a suitable temperature. The purification efficiency is usually greater than 98% and the output impurity levels can be maintained at less than 1–3 ppm for long times.