Head space gas chromatography with flame-ionization detection (HS-GC-FID), and purge and trap gas chromatography-mass spectrometry (P&T-GC-MS) have been used to determine methyl-tert-butyl ether (MTBE) and benzene toluene, and the xylenes (BTEX) in groundwater. In the work discussed in this paper measures of quality, e.g. recovery (94–111%), precision (4.6–12.2%), limits of detection (0.3–5.7 μg L⁻¹ for HS and 0.001 μg L⁻¹ for PT), and robustness, for both methods were compared. In addition, for purposes of comparison, groundwater samples from areas suffering from odor problems because of fuel spillage and tank leakage were analyzed by use of both techniques. For high concentration levels there was good correlation between results from both methods.

Results from P&T analysis showed that 20 of the 21 samples from the vulnerable areas contained MTBE at concentrations up to 666 μg L⁻¹. Levels in seven samples excessed maximum permissible levels for oder and taste set by the USEPA (20–40 μg L⁻¹); for thirteen of the samples levels were between 0.28 and 17.9 μg L⁻¹. The sensitivity of HS-GC-FID was, however, two to three orders of magnitude lower and concentration of 6–10 μg L⁻¹ could not always be detected, leading to false negatives. The same behavior was observed for analysis of BTEX-the lower sensitivity of HS-GC-FID and coelution of peaks led to results of poor reliability, and confirmation by GC-MS was always necessary. The applicability of two analytical methods widely used for routine monitoring of VOC thus depends on the organoleptic thresholds of MTBE and BTEX in groundwater (20 μg L⁻¹) and the need to survey trace concentrations of persistent MTBE in vulnerable aquifers.