Performance Assessment and Uncertainty Evaluation to Analyze Oxygen-18 Isotopic Content of Nitrate Using Modified Pyrolysis Technique

A method for measuring d18O content of nitrate has been developed. This involves combusting nitrate salt with activated graphite at 550 degree C for 30 minutes and cooling with a moderate cooling rate. Performance assessment of the whole developed analytical train was made using internationally distributed nitrate isotopes reference materials and real world sample of initial zero-nitrate content. The obtained results proved that the method is suited for handling samples of complicated matrices. Nitrate isotopic contents of some selected nitrate salts were measured using the modified procedure and some other well established methods at two different laboratories in Egypt and Germany. Finally, the uncertainty budget associated with the developed procedure was evaluated using the graphical nested hierarchal approach. Through this work, rapid, reliable, precise, catalyst-free, low-priced and less labor intensive offline pyrolysis technique for measuring O-18 content of nitrate has been modified and implemented