>>From: "Haraldur R. Karlsson" <[log in to unmask]>
>>Subject: New MS purchase (or old).
>>In-reply-to: <v01510104b100dd9033f8@[130.111.68.62]>
>>To: Stable Isotope Geochemistry <[log in to unmask]>
>>Message-id: <l03130301b1019489c461@[129.118.41.137]>
>>MIME-version: 1.0
>>Content-type: text/plain; charset="us-ascii"
>>
>>Dear Mike and others,
>>
>>I would like to add my two cents to this discussion.  Choosing a mass
>>spectrometer is in many ways like buying a car - it depends on your taste
>>and cash flow.  Just as in the case of a car the "dealership" is usally not
>>the best place to get advice on the quality of the "machine" or go for
>>service.
>>
>>I have used both Finnigans (Delta E precursor to Delta S and a 251) and VGs
>>(MM903 and SIRA-12) through the years (but not Europa's).  I realize that
>>these are not the lastest models but it appears to me that the basic design
>>of the machines has not changed or improved much over the years.  Last
>>year's RING TEST that involved hydrogen isotope analyses by many "old" and
>>"modern" instruments supports this notion.
>>
>>If I am correct the SIRA-12 was VG answer to the highly popular Delta E.
>>One of the first Delta E machine in the US was installed in Bob Clayton's
>>lab (which I was involved in) and many other labs followed Bob's example
>>purhcasing a Delta (Ironically the Delta E had to measure up to an
>>old-fashion double-collecting Nier Machine!).  My experience has been that
>>neither the Finnigans or VGs (I guess micromass) machines are perfect.
>>Each has its own quirks.  The Finnigans have a linear source but the VGs
>>may not.  I like the permanent magnet setup on the VGs better than the
>>electromagnet setup on the Finnigans.  Also the bellows design on the VGs
>>seems to last longer and is simpler to fix.   The Delta E is very compact
>>often difficult to get to the parts you want to fix.  The pumping systems
>>also vary - the Delta E has a more expensive pumping system (ion and turbo)
>>than the SIRA-12 (oil diffusion pumps).  The operating software on both
>>instruments was comparable and easy to use once the intial bugs were worked
>>out.  The first Isodat from Finnigan seemed a step backwards from the older
>>software because of its multitasking function (you were supposed to word
>>process while your mass spec did analysis, but this really never worked).
>>Another interesting tidbit is that the analysis precision on these VGs
>>appears to be almost 10X better than on the Finnigans which simply reflects
>>their way of calculating precision - the VGs report standard error whereas
>>the Finnigan give standard deviation.
>>
>>Cap Introne brought up a point of good care and avoiding a lemon.  Like
>>your car your mass spec will only perform well if it is taken good care of
>>but I honestly don't know how anybody can avoid a lemon - I suppose you
>>could run the mass spec through a series of tests.
>>
>>With regard to small samples, I found the SIRA-12 to perform slightly
>>better than the Delta-E (the automatic coldfinger freeze setup on the SIRA
>>is a nice feature) but in general I tell my students to make their sample
>>bigger since I worry a sample heterogenity at the mg level (e.g. soil
>>carbonates and limestones).  I know for example that on the SIRA-12 (even
>>with a microinlet) according to test run in England (I don't have the paper
>>at hand) the precision worsens below gas size of  less than about 5
>>micromol which corresponds to 0.5 mg CaCO3 (1mg CaCO3 yields 9.99 micromol
>>CO2 via acid dissolution).  If I can recollect correctly even the "big gun"
>>Finnigan 251 didn't give good precision for samples smaller than several
>>umoles.  Although, a priory, I would worry about obtaining good accuracy
>>for extremely small samples (e.g., 0.5 micromol or less) due not so much to
>>the mass spectrometer but the overall reproducibility (sample preparation -
>>blank, memory, etc.), others such as Cap (and the single foram folks) are
>>better judges of those issues than I am.
>>
>>As far as add-on devices, such as autocarb etc., I am old-fashioned and
>>prefer off-line systems.  First, I think these add-ons are extremely
>>expensive for what they do (carbonates and water) and can be built more
>>cheaply through third-party vendors (e.g., Brennikmeijer's automatic
>>all-glass systems).  Secondly, in case the add-on autoprep systems fails it
>>could cause a major problem for the mass spectrometer.
>>
>>I agree with Cap that I would prefer a series of smaller (Delta-S or VG
>>equivalent) dedicated mass specs rather than one super-instrument hooked up
>>to a multitude of front-end devices.  For example, I am not familiar with
>>ion sources that give optimum results for hydrogen isotopes on one hand and
>>C, N, O on the other.  I realize that funding agencies are usually only
>>interested granting funds for one instrument rather than two such that the
>>tendency is to go for the "big gun".  There are, however, many old
>>instruments out there, that can be gotten at reasonalbe expense and
>>upgraded (e.g., Delta E, MM602, MM903 etc.).  The fact that these
>>instruments are still around is a testament to their quality and durabilty
>>- just like old cars.
>>
>>With respect to service after the purchase and expiration the warranty I
>>would aviod the "dealerships".  One is far better of going with
>>independents such as Pro-Vac Services.
>>
>>Finally, choosing a mass spec really boils down to taste - VGs and
>>Finnigan's are pretty similar.  In my mind the ideal instrument would
>>incorporate the best aspects of both or the "Vinnigan".
>>
>>Good shopping,
>>
>>H.R.K.
>>
>>Dr. Haraldur R. Karlsson
>>Associate Professor of Geosciences
>>Department of Geosciences
>>Texas Tech University
>>Box 41053
>>Lubbock, TX 79409, USA
>>
>>(806)-742-3130 office
>>(806)-742-3112 lab
>>(806)-742-0100 Dept. fax
>>