STABILITY STUDIES AND PURIFICATION PROCEDURE FOR NITRITE SOLUTIONS INVIEW OF THE PREPARATION OF ISOTOPIC REFERENCE MATERIALS

The lack of reference materials: accurately certified for nitrite, is a problem in view of the importance of this species for environmental and medical reasons. This work outlines a plan for the preparation of nitrite isotopic reference materials (IRMs) in the form of high purity solutions, certified for their nitrite-nitrogen isotopic composition and nitrite concentration. To achieve the desired accuracy (expanded u ncertainty U with a coverage factor k = 2 of less than or equal to 2%) , primary methods of measurement such as isotope dilution mass spectro metry (IDMS), gravimetry, and titrimetry must be used. The main diffic ulty is the stability of nitrite. Other problems expected in the prepa ration and certification of nitrite IRMs are described. Results from l ong term stability studies (up to 1.5 years) and a procedure for the p urification of the candidate nitrite IRMs are presented. The purpose i s to use these IRMs for high accuracy method calibrations and as ancho r points for SI-traceable nitrite concentrations. Reference values lin ked to the SI system are useful to demonstrate the degree of internati onal comparability of nitrite measurements in intercomparison programm es such as the IRMM-International Measurement Evaluation Programme (IM EP). (C) 1998 Elsevier Science B.V. All rights reserved.