A sensitive and selective post-column detection system for nitrosamines is described. The principle upon which the detector works is that UV irradiation of aqueous solutions of nitrosamines leads to cleavage of the NNO bond. The amine generated is subsequent detected by chemiluminescence using tris(2,2′-bipyridyl) ruthenium(III), which is on-line generated by photo-oxidation of the ruthenium(II) complex in the presence of peroxydisulfate. Factors affecting the photochemical and chemiluminescent reactions were optimized to minimise their contribution to the total band-broadening. This detection system was tested for N-nitrosodimethylamine, N-nitroso-diethylamine, N-nitrosomorpholine, N-nitrosopiperidine and N-nitrosopyrrolidine, which were separated on an ODS column by isocratic reversed-phase chromatography with acetonitrile–water containing 5mM acetate buffer at pH 4.0. A linear relationship between analyte concentration and peak area was obtained within the range 0.13–500μgl −1 with correlation coefficients greater than 0.9995 and detection limits of between 0.03 and 0.76μgl −1 . Intra- and inter-day precision values of about 1.2% RSD (n=11) and 2.5% RSD (n=10), respectively, were obtained. The sensitivity may increase from 9 to 280 times with respect to UV detection, depending on the nitrosamine in question. An automated solid-phase extraction (SPE) system was used in conjunction with HPLC to determine nitrosamine residues in waters. Detection limits within the range 0.10–3.0ngl −1 were achieved for only 250ml of sample.