A primary xenon isotopic gas standard with SI traceable values for isotopic composition and molar mass

A metrological certification measurement was made on a large batch of xenon separated from the terrestrial atmosphere by Messer Griesheim (Duisburg, Germany). The measurements were performed using the same procedure for measurements of amount ratios as developed for the improvement of the Avogadro constant N-A. During the measurement, the gas effusion from the expansion vessel into the ion source was continuously monitored by measuring experimental values for [m(E-i)/m(E-j)](-(empty set)) to enable correction for mass discrimination. Synthetic mixtures were made of enriched Xenon isotopes and measured. They did not reveal a significant correction factor for residual unknown errors within the measurement uncertainty of 5 x 10(-4). Thus, an isotopic composition and a molar mass (atomic weight) value M(Xe) = 131.29276 +/- 0.00033 g mol(-1) for xenon in this batch was established by procedures confirmed by kinetic gas theory at this level. The measured isotope amount ratios were compared to previous measurements on atmospheric xenon. They are in good agreement but now have considerably smaller relative combined uncertainties: n(Xe-124)/n(Xe-132) = 0.003536(12); n(Xe-126)/n(Xe-132) = 0.0033077(72); n(Xe-128)/n(Xe-132) = 0.070989(29); n(Xe-129)/n(Xe-132) = 0.98112(41); n(Xe-130)/n(Xe-132) = 0.151290(47); n(Xe-131)/n(Xe-132) = 0.789055(76); n(Xe-134)/n(Xe-132) = 0.387819(69); n(Xe-136)/n(Xe-132) = 0.32916(17). Published by Elsevier Science B.V.