In sensing diluent gases which contribute to malodors in the human breath, a detection cell is housed within the hand-held cartridge made up of inner and outer casings movable between and open and closed position. The detection cell has an electrolyte interposed between inner and outer electrodes within the inner casing and when the cartridge is advanced to its open position a sample gas stream created by blowing into the interior of the cartridge is passed into contact with the inner electrode while a reference gas stream, such as, air contacts the outer electrode whereby an electric potential is developed in response to the presence of the diluent gases indicating the presence of malodors in the human breath.