Determining the concentration and15N abundance of the trace gases NO and N2O in air is difficult owing to their very low concentration in the atmosphere (NO < 1 ppb(v); N2O ≈ 0.32 ppm(v)). Although15N analysis of N2O in ambient concentrations can be carried out using a Gas Chromatograph Quadruople Mass Spectrometer (GC-QMS) and a dosage of 2 mL air by means of a sample loop, this system is not sensitive enough to measure the ambient concentration of NO and its15N abundance. Therefore the concentration of NO must be enriched by cryotrapping. The improved15N analytical apparatus described here facilitates the sensitive and sufficiently accurate measurement of the ambient NO with a15N abundance > 10at.% and thus represents an advance for15N2O analysis (better sensitivity).