SELECTIVE PHOTO-IONIZATION DETECTOR USING ION MOBILITY SPECTROMETRY

摘要

A photo-ionization detector (PID) (10) employs combinations of ion mobility spectrometry, ionization energy discrimination, and chemical filtering to identify the presence and quantity of specific gases. One such PID introduces a gas sample into an ionization chamber (14) at an end of a drift tube (16). UV light from a PI source (20) ionizes ionizable molecules contained in the gas sample. The PI source includes either multiple UV lamps (21), each having a specific energy level for discriminating between potential constituents of the gas sample or one multiple-energy level UV lamp with different light bandwidth window zones and a zone selector. A shutter grid (18) is open, an electric field in the drift tube attracts ions that travel against the flow of a drift gas until a collector electrode (32) at the end of the drift tube captures the ions. A time required for the ions to travel the length of the drift tube is characteristic of the type of ion. Thin mesh electrodes (30) in the drift tube sustain a uniform electric field so that groups of ions traveling down the drift tube to create well defined current pulses at the collector electrode.