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DIFFUSION vs.TURBOMOLECULAR PUMPING We have been using both DPs and turbos of medium capacity (150-200L/s) for high vacuum, i.e. < 10-8 mbar base pressure in the main chamber, for FT-ICR-MS for more than 10 years. Such Turbos are faster to put in action (10 mn) than DPs (> 30 mn). So one important consideration is power failures, frequent in our area. Turbos are generally faster to recover. They necessitate some maintenance, but now forever-lubricated ceramic ball bearing are almost the rule : check for maintenance costs with the seller and consider the possibility of mechanical and electronic repairs in the long run. We never used LN2 traps on DP, though I contemplated to put one. I am sure that most oil (alcanes) contamination comes for the rough pumps : a molecular sieve or alumina trap in the primary line is necessary. As stated previously, modern DPs generate very little backstream, particularly if the proper fluid is used (like polyphenylether for high vacuum applications). We also found that the maximum electrical heating power is not necessary for the optimum diffusion pumping efficiency, which was found at 180 instead of 220 V in our case. We use a closed loop chiller for both turbo or DP. A few weeks ago our 2 turbos (main + spare !) were both down, so we decided - reluctantly - to put back the DP : it was perfect even without change of the 7-years old fluid ! -------------------------------------------------------- J.-F. GAL Groupe FT-ICR-Chimie Physique Organique Fac. des Sciences-Parc Valrose Univ. de Nice-Sophia Antipolis 06108 NICE Cedex 2-FRANCE Tel : foreign (33) 492 07 61 10; domestic 04 92 07 61 10 Fax : foreign (33) 492 07 61 11; domestic 04 92 07 61 11 E-mail : lcpo@unice.fr --------------------------------------------------------Return to Top
Resolution should be defined as delta(m) over m. Resolving power is the reciprocal of this (see the classic "Mass Spectroscopy" by H.E. Duckworth et al). This is similar to the definitions in other spectroscopic and spectrometric fields (in physics). Kumar S. Sharma Atomic Mass Determinations University of ManitobaReturn to Top
My company is considering purchasing an ICP-MS for analyzing trace
metals in various materials. We are currently sending samples out for
analysis on ICP-MS (for many elements) or doing them in-house with
GFAA (for a few elements). We are planning on building an addition to
our current laboratory with clean room and analytical area as our old
lab is quite old and comparatively dirty.
1. The instrument would need to be rugged and relatively easy
to set up and maintain.
2. There are few samples (<10 per day) that require various
numbers of elements to be run. Sample prep varies.
3. Sample analyses range from <50 ppt to several percent.
Yes, I know, high TDS kills.
4. We have the whole range of in-house technicians: smart but
can't tie his shoes; can't run an AA but can fix your car and titrates
up a storm; etc.
I have heard the sales pitches and would like to hear from real users.
If there is anyone who would care to voice an opinion between PE and
HP, please do so. I have looked at POEMS and can't justify it and I
have looked at the major vendors. It's down to PE and HP so please
keep comments to them. TIA.
DamnULP
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I never get lost because people are always telling me where to go.
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I have two answers to all things that happen: "Wow, Cool!" and
"Shit Happens."
Return to TopLooking for a supplier which can deliver 20 micron ID steel capillaries ? Does anyone know whether these exist ? Eddy L. EsmansReturn to Top