Low ppb Levels of BTEX in water by Headspace GC

We have used a PID Analyzers GC312 (portable GC) with a photoionization detector (PID) http://www.hnu.com/ for analysis of VOC's in water using the headspace method (40 ml VOA vials). The sample injected was 0.2 cc of headspace. A 1 ppm mix of 524.2 was prepared as a standard. The BTEX compounds were identified and used as standards for analysis of unknown field samples. A 30M x 0.32 mm id with a 5 micron film of methyl silicon ( http://www.vici.com/ The chromatogram for the standard is shown below:

One of the samples containing 20 ppb of BTEX  is shown below:

The sensitivity of the method is displayed in the following sample that was found to contain 3 ppb of benzene:

This method clearly has ppt level capability by simply injecting a larger sample volume eg 1 cc instead of 0.2cc. The headspace GC method is ideal for field measurements since it  requires little incremental equipment (40 ml VOA vials, 1 cc gas tight syringe) and is easy to implement.