A primary isotopic gas standard for krypton with values for isotopic composition and molar mass traceable to the Systeme International d'Unites

Isotope amount ratios of krypton were measured on subsamples from one large batch of high purity krypton separated from the atmosphere. Synthetic mixtures of enriched krypton isotopes were used to "calibrate" the measurements with small uncertainties. The result is a primary isotopic gas standard (PIGS) IRMM-2030 with certified values for isotope ratios, isotopic composition, and molar mass of krypton with small combined uncertainties u(c), evaluated according to the ISO/BIPM Guide (GUM). It is commercially available from IRMM-Geel or from MESSER (Duisburg, D). The certified krypton isotope amount ratios in the PIGS IRMM-2030 are as follows: n(Kr-78)/n(Kr-84)=0.006 232 5(55), n(Kr-80)/n(Kr-84)=0.040 107(17), n(Kr-82)/n(Kr-84)=0.203 43(17), n(Kr-83)/n(Kr-84)=0.201 79(11), and n(Kr-86)/n(Kr-84)=0.303 205(59) with expanded uncertainty U=ku(c) and coverage factor k=2, The molar mass of Kr in this sample is M(Kr)=83,798 02(16) g/mol. These values are in good agreement with published measurements of atmospheric krypton but have smaller combined uncertainties and are "calibrated" by means of synthetic isotope mixtures. The values of the PIGS are traceable to the SI. Measurements of isotope amount ratios of krypton in other samples can be linked to SI using this PIGS. (Int J Mass Spectrom 206 (2001) 129-136) (C) 2001 Elsevier Science B.V.