Certification of a 15N-enriched nitrate species-specific spike isotopic reference material IRMM-627

Abstract

A new 15N-enriched nitrate species-specific spike isotopic reference material IRMM-627 has been prepared in the form of KNO 3 in NaOH solution (pH = 10). It is a 64.6% enriched 15N-nitrate material, certified for its nitrogen isotope ratio (in nitrate species) n( 14NO 3 −)/ n( 15NO 3 −) = 0.548 ± 0.012 and its nitrate concentration c(NO 3 −)/mmol 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 mass spectrometric procedure was determined using synthetic isotope mixtures. Isotopic homogeneity, stability and impurity content of IRMM-627 were investigated. Orthodox uncertainty evaluation 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(NO 3 −)/mmol kg −1 > 0.016. It is available in quartz ampoules containing approximately 4.5 g of solution.