Surface ionization organic mass spectrometry (SIOMS) was applied to some s-triazine herbicides (simazine, atrazine, simetryne, ametryne and prometryne) by using quadrupole mass spectrometry in which the thermal ion source has a rhenium oxide emitter. The mass spectra were interpreted in a purely empirical way by means of evidence from previous investigations, and then compared with conventional electron impact ionization techniques. Sensitivity and selectivity were also studied, demonstrating that (i) these herbicides are efficiently surface ionized, (ii) in the SI mass spectra all s-triazines exhibited the M' molecular ion as the base peak with only relatively minor fragment species, with the exception of prometryne, (iii) the experimental results rationalized the high sensitivity of surface ionization detection (SID) in gas chromatography (GC) for the herbicides examined and (iv) GC/SIOMS coupling can be used for the sensitive and selective detection of these herbicides in the water. An approach to the detection of these herbicides in water by GC/SIOMS and GC/SID is described. The characteristics of both methods provide a reliable, sensitive and selective method which is needed for low concentration level measurements in complex mixtures.