An Apparatus for collecting volatile compounds in human breath includes adevice fordiscriminating between alveolar and non-alveolar portions of exhaled breath byreal-timemeasurement of a physical characteristic of said exhaled breath； a device formeasuringvolume of exhaled breath； a chamber with piston or similar compressible devicewithclean internal surfaces designed to collect a precise volume of the alveolarportion of theexhaled breath； a pump to draw the exhaled breath collected in the chamberthrough atleast one sorbent tube； a subsystem for introducing a clean compressed gasinto thechamber to expand it, and for purging the internal tubing of the system； and asubsystemfor selectively collecting a room air sample. A manifold for receiving atleast one sorbenttube includes an input block having at least one open-topped channel forreceiving aninput end of a sorbent tube, and an input port within the open-topped channelconfiguredto be in fluid communication with an input end of the sorbent tube； an outputblockhaving at least one open-topped channel for receiving an output end of asorbent tube,and an output port configured to be in fluid communication with an output endof thesorbent tube； and a locking lever associated with at least one of the inputand outputblocks for moving the input and output blocks linearly towards and away fromeach otherbetween fully open and closed positions.
