GC has columns that can separate the gases based on their molecular weights, or their interaction with the column material. You need some kind of detector (mass spectrometer or FID) to quantify these gases. The GC column separates these gases which are then passed through the detector to measure the concentration.

There is difference between fluoride and Fluorine. Fluoride is not a gas. Even Inductivily Coupled Plasma mass spectrometer can not estimate Fluoride.

I am more specific about HF in the exhaust gas obtained from industries.

In GC you can use various detectors like FID. GC-MS will be more useful that GC to identify the accurate concentration.