CERTIFICATION OF A N-15-ENRICHED NITRATE SPECIES-SPECIFIC SPIKE ISOTOPIC REFERENCE MATERIAL IRMM-627

A new N-15-enriched nitrate species-specific spike isotopic reference material IRMM-627 has been prepared in the form of KNO3 in NaOH soluti on (pH = 10). It is a 64.6% enriched N-15-nitrate material, certified for its nitrogen isotope ratio (in nitrate species) n((NO3-)-N-14)/n(( NO3-)-N-15) = 0.548 +/- 0.012 and its nitrate concentration c(NO3-)/mm ol kg(-1) = 3.124 +/- 0.080 (expanded uncertainty, coverage factor k = 2). The isotopic composition was determined using negative thermal io nisation mass spectrometry and the concentration via reverse isotope d ilution mass spectrometry (IDMS). The mass fractionation of the mass s pectrometric procedure was determined using synthetic isotope mixtures . Isotopic homogeneity, stability and impurity content of IRMM-627 wer e investigated. Orthodox uncertainty evaluation was done by examining the different uncertainty contributions. The species specific spike is otopic reference material can be used to perform isotope dilution anal ysis of nitrate with c(NO3-)/mmol kg(-1) > 0.016. It is available in q uartz ampoules containing approximately 4.5 g of solution.