I know you can use GC-MS for the analysis of gaseous molecules, but would you be able to instead use an infrared spectroscopy method to analyse gaseous molecules, or does it need to be mass spectroscopy?
GC-MS is just one common method of what is known as 'hyphenated' analysis. GC-IR instruments do exist (see examples), although usually involve some pretty specialised cells to allow for gas flow through the sensor. Hyphenated instruments are limited pretty well by your imagination (and budget) only. LC-NMR-MS is a great example of extended hyphenation, and is a powerful emerging tool for automated analysis of complex sample mixtures.