Abstract: A chemical cell (40) containing silver nitrate is connected at the inlet (10) of an ion mobility spectrometer (1) so that sample gas for detection flows to the IMS via the chemical cell. When the sample gas contains arsine or phosphine, to which the IMS is not normally sensitive, this is converted by the silver nitrate in the cell (40) to nitric acid, to which the IMS is sensitive. In order to distinguish between nitric acid produced in response to arsine or phosphine and nitric acid present in the sample gas before supply to the cell (40), the inlet (10) is switched to receive sample gas directly.

Abstract: An IMS or other detection system has an entry gate (3) controlled by a pseudo-random binary sequence that is bit-flipped to reduce noise. Matrix algebra is used to carry out deconvolution and analysis of the cell output.