Dear Attila, second possibility is the O-ring joint. Use a touch of vacuum grease (not >Apiezon!) to help the gasket be deformed smoothly. This helped me when I >used such joints. What's the matter with Apiezon grease? I don't use it for carbonate work, but both N and T are widely used in the lab ... Clemente ----------------------------------------------- Dr. Clemente Recio Stable Isotope Laboratory Fac. de Ciencias Univ. de Salamanca E 37008 - Salamanca Spain Phone: (+34) 23 29 44 00 Ext. 1540 Fax: (+34) 23 29 45 14 E-mail: [log in to unmask] -----------------------------------------------