If you are looking for ppm H2S in liquid hydrocarbons, talk to Antek. Otherwise, as TDK stated, GC s very common. The bigger challenge in my view is ensuring that the sample points are well designed, especially for taking samples of streams with high concentrations of H2S. Safety is paramount!
Drager tubes or Gastec tubes will work also if the concentration is low and you're not looking for great accuracy. The tubes are not just for concentrations in air (can also be used for gas streams), but whoever is testing the stream must follow the correct procedure (sampling and safety).
Here is the way I was taught to take samples using Drager:
If you are using a Drager with a hand pump, you first have to build a "T" apparatus...using a small ss T fitting with plastic tubing connected to all three ports. The middle "port" would be a purge...to ensure that you are not pressuring the gas through the Drager tube which would result in an erroneously high reading. You also have to have enough purge to ensure that you are not sucking air instead of sample.
1. First connect one of the tubes hanging off of the T to the sample point.
2. Fit a Drager tube into the hand pump, and then connect the other end of the tube to another one of the plastic tubes. Note that the sample must flow through the tube in the proper direction.
3. Start a very tiny flow of the sample gas...just enough that (if safe to do so) you would barely feel it blow on the back of your hand.
4. Pump the number of pumps required for the tube selected. Then, shut off your sample flow and disconnect everything. Read the result off the tube.
Obviously, the "tube" method is a type of open loop sampling. You have to ensure that you are applying this only to samples where the worker will not be at risk from exposure.
Be careful out there...always use the proper PPE for the job.
Lead Acetate Tape analyzers are also very common for measuring H2S. They're often preferred because they're relatively inexpensive. GC's are also used, but more often for total sulfur measurement rather than just H2S.
-Chris
