Sequential diffusion of ammonium and nitrate from soil extracts to a polytetrafluoroethylene trap for 15N determination

Abstract A novel diffusion method was used for preparation of NH4+- and NO3−-N samples from soil extracts for 15N determination. Ammonium, and nitrate following reduction to ammonia, are allowed to diffuse to an acid-wetted glass filter enclosed in polytetrafluoroethylene tape. The method was evaluated with simulated soil extracts obtained using 50 ml of 2 M potassium chloride solution containing 130 μg of NH4+-N (2.3 atom% 15N) and 120 μg of NO3−-N (natural 15N abundance). No cross-over in the 15N abundances of NH4+-N and NO3−-N was observed, indicating a quantitative diffusion process (72 h, 25°C). Owing to the presence of inorganic nitrogen impurities in the potassium chloride, the 15N enrichments should be corrected for the blank nitrogen content.