Abstract Passive and active ammonia (NH 3 ) sampling devices have been tested for their nitrogen (N) capture potential and δ 15 N fractionation effects. Several sampling techniques produced significantly different δ 15 NH 3 signals when sampling the same NH 3 source released from field site fumigation campaigns. Conventional passive NH 3 ‐monitoring systems have shown to provide insufficient N for isotope‐ratio mass spectrometry and various modified devices have been developed, based on existing diffusion tube designs, to overcome this problem. The final sampler design was then tested in a wind tunnel to verify that sampling NH 3 in different environmental conditions did not significantly fractionate the δ 15 N signal. Copyright © 2005 John Wiley & Sons, Ltd.