Thomas and others:

        We have also been analyzing methane at low concentration in
seawater and some air samples (Popp et al. 1995, Anal. Chem. 67, 405-411;
Sansone et al. 1997, Anal. Chem. 69, 40-44; Reeburgh et al. 1997, Geochim.
Cosmochim. Acta. 60, in press).  Unfortunately, the concentration of CH4 in
RM 8559, RM 8560, RM 8561 are far too high for our instrument and are not
representative of our samples.  We check the calibration of our instrument
with either 100 ppm or 25 ppm CH4 in He.  If anybody is interested in
participating in a laboratory intercalibration of such gases, please
contact us so we can work out how best way to package and send exchange

        We would also like to do a similar exercise for d18O-d15N in N2O;
again low-levels (100-200 ppm as well as pure N2O).


            Brian N. Popp, Associate Professor
University of Hawaii, Department of Geology and Geophysics
         2525 Correa Road, Honolulu, Hawaii 96822
            (808) 956-6206 Fax: (808) 956-7112
WWW Site: