Purification procedure for delta N-15, delta O-18, Delta O-17 analysis of nitrate

A solid phase extraction technique has been developed for purification of nitrate in environmental solutions for isotopic analysis. Three materials, C18, silica gel and cross linked poly-vinylpyrrolidone, were used to remove non-polar, slightly polar and humic compounds from solutions with high dissolved organic loads. The clean up procedure does not impact the isotopic composition of the nitrate analyte for samples in the 2-6mg (NO3-) range and improves accuracy and precision of the oxygen and nitrogen isotope analysis using the AgNO3 decomposition and thermal conversion elemental analysis techniques.