A miniature gas chromatograph (GC) and miniature Paul ion trap (PT) mass spectrometer system has been developed for identifying and quantifying chemical species present in closed environments having a complex mixture of gases. Inherent to the system are high sensitivity, good dynamic range, good PT resolution, low GC flow rates to minimize pump requirements and the need for consumables, and the use of a modular approach to, in future work for example, extract and identify volatile organic compounds dissolved in water. Measurements are reported on system response to gaseous species at concentrations varying over four orders of magnitude. The GCPT has a mass, volume, and power that is, conservatively, 1/20th that of commercial off-the-shelf systems. Potential applications are to spacecraft cabin-air monitoring, robotic planetary exploration, and trace-species detection for (terrestrial) residual gas analysis and environmental monitoring.