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.