The kinetics of organics purging In the purge-and-trap gas chromatography/mass spectrometry technique for the concentration of volatile compounds In water using primary fragment Ions In modified method 524,2 Is revealed to be first order with respect to purging time. This kinetic model Is applicable from a concentration of 200 ppb for ketones and nitrogen compounds to the sub-ppb levels for more readily purgeable volatile compounds. The purging ratios of the compounds, as well as their first-order purging rate constants, are obtained. The rate constant can be used as an alternative guide to gas chromatographic retention time for the selection of Internal standards for quantitation purposes and/or replacement of surrogates for performance and quality assurance.