Nitrogen isotope fractionation factors (α) measured and estimated from the volatilisation of ammonia from water at pH 9.2 and pH 8.5

摘要

This paper examines the nitrogen isotope fractionation factors (alpha) associated with the volatilisation of ammonia from water under controlled conditions at two pH values (8.5 and 9.2). This experiment assumed the continuous removal of ammonia at a single purge rate of 10 mL air min(-1). The fractionation resulting from the removal of total ammonia from the water into an acid trap was named the observed isotope fractionation factor (alpha(obs)), and it was measured as 1.019 (+/- 0.0025) at pH 8.5 and 1.030 (+/- 0.0025) at pH 9.2. The observed isotope fractionation factor includes the equilibrium isotope fractionation factor (alpha(eq)) and the kinetic isotope fractionation factor (alpha(kin)), each one mathematically derived from the experimental data. The equilibrium and kinetic isotope fractionation factors were estimated as alpha(eq) = 1.036 (+/- 0.0014) and alpha(kin) = 1.050 (+/- 0.003), respectively. Our results are compared to other previously measured and estimated fractionation factors.