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