A method utilizing computerized gas chromatography-mass spectrometry (GC-MS) is presented for qualitative and quantitative determination of volatile organics in drinking waters, natural waters, or industrial effluent waters. It is based on the addition of deuterated internal standard, 1,2-dichlorethane-d₄, to an appropriate-sized portion of sample and use of the Bellar-Lichtenberg method of purge-trap-desorb into determinative instrument. Method validation consisted of analyzing volatile priority pollutants at 2, 10, 50, 100, and 200 ppb with internal standard at 20 ppb in each of seven replicate analysis at each dose. Comparison of relative standard deviations (RSD) of internal and external standard methods of GC-MS analysis revealed no significant differences. This study also yielded valuable information concerning repeatability, reproducibility, stability of internal standard, linear dynamic range of GC-MS, and RSD variation with different area regenerations of diagnostic atomic mass units. Pollutant identification is based on retention time and total mass spectral comparison with authentic compound. Quantitation is based on measurement of the areas of retrieved diagnostic atomic mass unit regeneration of contaminant and internal standard. Using response factors determined from analysis of standard mixtures containing compounds of interest and internal standard, and the known mass of internal standard, the concentration is calculated. Lower detection limit for the volatile priority pollutants is approximately 1 μg/litre. This method has detected several volatiles that are not Environmental Protection Agency priority pollutants.