I was not questioning the difference between the 252 and the 253. The higher water background here could be due to rotary pump oil cracking in the analyser rotary on your 253. We had this problem this past spring when we had an unusually high water background on a Delta XP. After checking everything, I called Peter Stow asking what else we may have forgotten and sure enough I had a "D'OH!" moment when he asked about our last oil change on the main pump. This was the only one we had not changed during our annual Christmas maintenance due to the timing of the arrival of this pump in the previous year. It turns out the "oil" of this Pfeiffer was on its way to 1.5-2 years old; a sure fire way to get high water background in the source.
I was simply stating the difference seen on the Delta V Plus regarding the water (mass 18 vs mass 44) background. The higher transmission of water may be more of a mass issue than a sensitivity issue (molecules per ion). Since all instruments specs are on CO2 and H2 (H3+ factor) then a rethink of the way water behaves with this particular source was needed for background checks.
De : Stable Isotope Geochemistry [mailto:[log in to unmask]] De la part de Herbert Tobias
Envoyé : 22 décembre 2007 19:33
À : [log in to unmask]
Objet : Re: [ISOGEOCHEM] SS analyzer vs Al analyzer
I believe the "higher" water background measurement in different IRMS
instruments is not due to higher transmission/sensitivity. First, Gilles
states sensitivities between two instruments that are not 10X different
(actually a 1/3 higher in one versus the other).
In our lab, we operate a MAT252 & a fairly new MAT253. With CO2
injections through a GCC interface, the MAT252 response is near the MAT253
(within less than a factor of two). Nevertheless, the water background in
the two systems differ by almost two orders of magnitude! (MAT252=~7-50mV,
MAT253=~1000-5000 mV). Tell me if my initial conclusion (up top) is wrong
based on the numbers. Just FYI.
> Hi Wolfram
> The "higher" water background is usually seen on the Delta V PLUS not on
> the Delta V Advantage or previous generation instruments. For example, on
> CO2 (mass 44) in dual-inlet you get:
> Delta V Advantage and older Delta Plus generations: 1200 molecules per ion
> Delta V Plus: 800 molecules per ion
> The water background (mass 18) looks worse because it has almost 10 times
> better transmission to the collectors with the V Plus's refined optics. To
> compare to the other instruments you divide by ~10 the water signal. So
> there isn't more water in the source; it is just the transmission to the
> collectors that falsely indicates worse.
> Gilles St-Jean
> Chercheur / Research Scientist
> Université d'Ottawa / University of Ottawa
> Sciences de la Terre / Earth Sciences
> 140 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5
> Tel: 1-613-562-5800 xt 6830 (Bureau / Office)
> xt 6839 (Bureau / Office Lab)
> xt 6836 (IRMS lab)
> Téléc. / Fax: 1-613-562-5192
> Courriel / E-mail: [log in to unmask]
> Toile / Web: www.isotope.uottawa.ca
> -----Message d'origine-----
> De : Stable Isotope Geochemistry [mailto:[log in to unmask]] De la
> part de Wolfram Meier-Augenstein
> Envoyé : 18 décembre 2007 08:04
> À : [log in to unmask]
> Objet : Re: [ISOGEOCHEM] SS analyzer vs Al analyzer
> Dear Sarthak,
> You are not alone with these questions. I too would be interested to learn
> what Delta-V users experiences are in this respect.
> Some Delta-V users have mentioned to me seeing rather high water
> background readings (higher than on other instruments in the same lab),
> something that may or may not be related to the source seal material.
> Another question would be if long-term use (> 3 years) would result in
> noticeable ion burn effects on the analyzer material?
> From: Stable Isotope Geochemistry [[log in to unmask]] On Behalf Of
> Sarthak Chakraborty [[log in to unmask]]
> Sent: 18 December 2007 04:45
> To: [log in to unmask]
> Subject: [ISOGEOCHEM] SS analyzer vs Al analyzer
> Dear All,
> I have a technical query which I like to get an answer from the users
> rather than from the manufacturer.
> The Thermo Fisher has introduced an aluminum alloy based analyzer instead
> of stainless steel in their Delta V Plus CF IRMS. I would like to know if
> it may affect the vacuum in general and particularly the long term
> performance of the machine.