Certification of a 15N-Enriched Nitrate Species-Specific Spike Isotopic Reference Material IRMM-627

A new 15N-enriched nitrate species-specific spike isotopic reference material IRMM-627 was prepared in the form of KNO3 in NaOH solution (pH = 10). It is a 64.6% enriched 15N-nitrate material, certified for its nitrogen isotope ratio (innitrate species) n(14NO3)/n(15NO3) = 0.548 +-0.012 and its nitrate concentration c(NO3)/mmil.kg-1 = 3.124+-0.080 (expanded uncertainty, coverage factor k = 2). The isotopic composition was determined using negative thermal ionisation mass spectrometry and the concentration via reverse isotope dilution mass spectrometry (IDMS). The mass fractionation of the MS procedure was determined using synthetic isotope mixtures. Isotopic homogeneity, stability and impurity content of IRMM-627 were investigated. Orthodox uncertainty evalaution was done by examining the different uncertainty contributions. The species specific spike isotopic reference material can be used to perform isotope dilution analysis of nitrate with c(NO3)/mmol.kg-1>0.016. It is available in quartz ampoules containing approx. 4.5 g of solution.JRC.D-Institute for Reference Materials and Measurements (Geel