Inorganic compounds such as hydrides has low ionization potentials and can be detected by a photoionization detector (PID) at low ppb levels with GC-PID. A chromatogram of low ppb levels of AsH3 and PH3 is shown below:
The PID has detection limits in the low ppb range for many of the hydrides and other inorganic compounds. Arsenic in water has been shown to have a detection limit of 0.075 ppb in a paper "Total and Speciated Arsenic Compounds in Water by Photoionization and Gas Chromatography/PID" to be published in "Toxic Trace Metal Remobilization & Remediation - A Geochemical Body of Work" to be published by the ACS in 2012.
PID Analyzers has a broad range of products from GC Detectors (six to choose from) to Lab & Portable GC to the PeakWorks Software. These are shown below and more info is available on or website: http://www.hnu.com .