Mimi, We have a similar setup in our lab (GFL 1086 interfaced to a Delta Plus)and have had some of these problems in the past. You may want to check your hoko sticks or hoko beads for the HD analysis. Are they new? If not, what types of samples were analyzed in the past using those same sticks? You will also want to check for consistency in temperature throughout the bath. It may be cooler or warmer at one end causing the problems you are seeing. I am not sure how to avoid this problem except to circulate the water through the system at a constant temperature. You may also want to recheck your equilibration flasks for leaks (even small ones). I hope this helps. Art -- Art Kasson Cornell Isotope Laboratory Dept Ecology and Evolutionary Biology E440 Corson Hall Tower Road Ithaca NY 14853 USA Phone: 607.254.1382 Fax: 607.255.8088 COIL website http://www.cobsil.com Isogeochem website http://www.isogeochem.com