Hello >Does anyone have any experience of cleaning the stainless steel >bellows and inlet assembly of the dual inlet used on the Thermo MAT >253 isotope MS? Our 253 has been contaminated by oil/water from the >pneumatic system and has been out of action now for 15 months. The >contamination was due to the failure of a gold gasket in a valve on >the change-over assembly. Advice to keep baking the instrument may >actually have made the situation worse by moving the contaminant, >via un-crimped capillaries, around the inlet and into the bellows. >However, we think that the 253 mass spectrometer itself is OK and we >have replaced the C/O valve and capillaries. We are still getting >large transitions of 13C and 18O when conducting zero enrichment >between sample and reference inlet. >The old method of cleaning stainless steel vacuum systems was to use >hot trichloroethylene followed by isopropanol. Is it OK to still use >this method? We have ultrasonic baths and vacuum ovens at our >disposal. I also think a torque wrench should be used to tighten the >gold seal valves, does anyone know a suitable torque setting? > >The pneumatic system on this instrument leaked like a sieve, and >this was why oil vapour reached the valve seatings. I >recommend anyone using oil compressors to make sure there are >minimal leaks. Its a good idea to use a flow meter to monitor the >air flow and allowing for a 1 Bar pressure drop across the meter. We >have since switched to using dry nitrogen to drive the pneumatic valves. John John Hill Mass Spectrometry Facility University College London Chemistry Department 20 Gordon St. London WC1H 0AJ Tel: 020 7679 4605 Fax: 020 7679 7451