introduced into flow path 26 through clean air inlet 66 via recirculator pump 14 a fig5 drawing in clean dry air assists in reducing the faim spectrometer 39 s sensitivity to humidity moreover if the spectrometer is operated without clean dry air and a known gas sample is introduced in the device the device can be used as a humidity sensor since the resulting spectrum will change with moisture concentration from the standardized spectrum for the given sample however rather than each filter 32 a e of filter array 62 sharing the same flow path 26 individual flow paths 26 a e fig7 may be provided so that each flow path has associated with it for example inlet 16 a ionization region 18 a confining electrodes 56 a u2032 56 b u2032 ion filter electrode pair 20 a 22 a detector electrode pair 33 a 35 a and exit port 68 a in operation sample gas 12 enters sample inlet 16 a fig8 and is ionized by for example a corona discharge device 18 a the ionized sample is guided towards ion filter 24 a by confining electrodes 56 a as ions pass between ion filter electrodes 20 a and 22 a undesirable ions will be neutralized while selected ions will pass through filter 24 a to be detected by detector 32 a as shown in fig9 multiple simultaneous detections were made of benzene peaks 50 and acetone peaks 51 demonstrating the advantage of the arrayed.