A PID Analyzers Model 312 GC (http://www.hnu.com) with a photoionization detector (PID-10.6 eV lamp) is shown below and was used to detect ppt (parts per trillion) levels of benzene in an air nitrogen mix. A 100 ppb standard of benzene in air was diluted with prepurified nitrogen to obtain ppt levels of benzene. A chromatogram with 500 ppt of benzene is show in the Figure below.
The column was a 30M x 0.32 mm id with a 5 micron film of methyl silicon ( http://www.vici.com/). The column flowrate was 6 cc/min of hydrogen with an additional makeup of 6 cc/min. The temperature was isothermal at 120C. The sample was injected with a 10 port valve that had a 0.2 cc loop.
Our PID, with a sealed window, is the most sensitive one available since ppt levels of aromatics can be detected by direct injection without preconcentration. This detector has a very wide dynamic range of 108.