Abstract
A procedure suitable for measuring d(18)O-NO3- in waters with moderate ionic strengths and high DOC loads has been established. The conditions necessary to effect complete nitrate recovery and complete removal of other oxygen containing anions and DOC without scarifying the isotopic signature of nitrate were investigated. The wet chemistry train developed for extraction and purification of nitrate from the liquid matrix consists of the following consecutive steps: sulfate precipitation using barium hydroxide, filtration, cation exchange, anion exchange, elution, neutralization and adsorption. A mixed neutralization scheme comprising neutralization using silver oxide and potassium hydroxide has been devised and implemented. Many DOCs removal pathways have been evaluated with regard to their DOCs removal efficiency and negative effects on sample - nitrate pool as well as the oxygen isotope composition of nitrate. Preservation experiments revealed that addition of 1/4 ml chloroform (99.8%) per one liter sample is an effective way of preserving nitrate pool.