Several years ago we developed a headspace GC method for the analysis of H2S which was an impurity in a liquid drug formulation. We used a nitrogen-phosphorus detector and a DB-VRX column I believe. If you are trying to sample the gas phase directly than headspace probably isn't the best sampling approach, and there are probably better methods out there regardless, but we were able to use this approach to develop an accurate and precise method for H2S.