Preparation and characterization of IAEA‐603, a new primary reference material aimed at the VPDB scale realisation for δ 13 C and δ 18 O determination

RATIONALE NBS19 carbonate, a primary reference material (RM) for the VPDB scale realisation introduced in 19871 , was exhausted in 2009, and no primary RM was available for several years. This study describes the preparation and characterisation of a new RM, IAEA-603, (Ca-carbonate, calcite of marble origin) which shall serve as a new primary RM (replacement for NBS19), or primary calibrator aimed at the highest realisation of the VPDB scale for δ13 C and δ18 O values, including the VPDB-CO2 δ18 O scale. METHODS IAEA-603 preparation and characterisation (value transfer) against NBS19 were performed by addressing the major modern technical requirements for RM production and characterisation (ISO Guide 352,3 ). IAEA-603 was produced in a large quantity, and the first batch was sealed into ampoules (0.5 g) to ensure RM integrity during storage; four other batches were sealed for long-term storage. The most accurate method of CO2 preparation for isotope mass spectrometry was used, namely carbonate-H3 PO4 reaction under controlled conditions. RESULTS The assigned values of δ13 C= +2.460±0.010 ‰ and δ18 O= -2.370±0.040 ‰ (k=1) are based on a large number of analyses (~10 mg aliquots) performed at IAEA and address all the known uncertainty components. For aliquots down to 120 μg, the δ18 O uncertainty remains unchanged but shall be doubled for δ13 C. The uncertainty components considered are as follows: (i) material homogeneity (within and between the 5200 ampoules produced), (ii) value assignment against NBS19, (iii) storage effects and (iv) effect of the 17 O correction. CONCLUSIONS The new primary RM IAEA-603 (Ca-carbonate, calcite of marble origin) replaces NBS19 in its use as the highest calibrator for the VPDB δ13 C and δ18 O scale, including the VPDB-CO2 δ18 O scale. The use of IAEA-603 will allow laboratories worldwide to establish consistent realization of the scales for δ13 C and δ18 O values and metrological comparability of measurement results for decades. The VPDB scale definition based on NBS19 stays valid.