Analytical instrument - CRDS isotope monitor - an instrument for automated monitoring of environmental levels of methane. Both mixing ratio and stable carbon isotope composition must be measured. The instrument must be field deployable and work without cryogens and generate data with a time constant <180 seconds. It will largely be based on a climate observatory in the tropics and seldom be re-located. We now request information on the state of the art with respect to these kinds of measurements.