Dave,

We have both the AS200 and the AS128 and both have low N2 blanks (not
detectable) on the CE NC2500 EA if properly maintained.  Both have good and
bad points about repair and maintenance, we prefer the AS128 so that we can
run filter samples without clogging, but that is an EA issue

That is not the issue with the TCEA which runs the graphite reactor at 1400
or 1450 degrees C.  The connection tube on the autosampler is cooled with a
fan and the outer portion of the tube gets hot, but not too hot.   The
AS128 tube is about 3" high and the AS200 tube is shorter and srews up into
the bottom of the unit so the autosampler sits lower over the reaction
tube.  The plastic slide on our AS200 actually melts onto the polished
metal plates with continued use and the instrument and silver boat blanks
rise and are isotopically variable.  This is the problem with the AS200,
that we do not see with the AS128.

It may be possible to get longer connection tubes to screw into the bottom
of the AS200 and raise the whole unit up several inches, Bruno do you sell
something like that or do we have to get this made in our machine shop?  We
have also looked into getting a collar to go around the autosampler
connection tube and connect it to a chiller/circulator like we have on all
the turbo pumps.

It is the heat rising up from the center of the reactor up into the
autosampler that is the problem, and the temperature tolerances of the
materials that make up the inside of the autosampler.  Not much you can do
if they melt.

Hope this clears up the confusion.

Bill


At 12:14 PM 10/31/00 -0700, you wrote:
>If this msg is in reference to the AS128 autosamplers sold by CE I would
>recommend against its purchase others may have a different opinion which
>should also be shared. However, I have used both the AS200 and the AS128 on
>our 12 yr old CE1500 EA and found that the AS200 is a more robust unit but

>it does have a relatively large blank (depending on the condition of the
>slide and its adjustment) compared to the AS128. The AS128, in my opinion,
>is a maintenance headache. Either the advance pin would break or it would
>go out of adjustment for one of a number of reasons. In addition the more
>drums you would add the worse it would behave. Since we run lots of filters
>we needed the larger sample holes. I did what I could to make modifications
>to the unit but decided that the carousel was not worth my time or money.
>
>My solution has been the carousel that Bruno at Costech provides. I have
>been using it for a number of months with very good success. It is
>presently designed to run either a 32 (31 samples) or 50 (49 samples) hole
>drums on the same unit. All you need to do is change out one drum for the
>other, flip a switch, purge the sample drum, and start running. Since the
>sample drum is sealed and in helium there is essentially no blank. The
>carousel is designed to simply rotate and drop the sample over an open
>hole. There is not slide or rotating cone to fuss with or worry about
>damaging. I am not sure how the carousel will work on the TC/EA but I'm
>sure Bruno could answer this question. If you need the small or large
>volume holes and want a zero blank then I would consider contacting Bruno
>and see if this is something you could use.
>
>Cheers,
>
>Dave
>
>PM 10/31/2000 +0100, you wrote:
>>Dear members & friends of pyrolysis,
>>
>>Have you got the same experience (large blank) like Bill with his AS200
>>autosampler ?
>>I will interesting with this problem, because next months we'll make the
>>acquisition of this configuration, that is true Finnigan suggest the AS128
>>but is it the only one for have good results ?
>>
>>
>>Régis Guérin
>>Eurofins Scientific
>>rue P.A.Bobierre BP 42301
>>F-44323 Nantes cedex 03-France
>>tél : (33) 2 51 83 21 00 - fax : (33) 2 51 83 21 11
>>email : <mailto:[log in to unmask]>[log in to unmask]
>
>****************************************************************************
>David A. Mucciarone
>Laboratory Manager
>Stanford University
>Department of Geological and Environmental Sciences
>Building 320, Room 118
>Stanford, CA 94305-2115
>650-723-0817 (office) 650-725-2199 (fax)
>Office - Green Earth Sciences Rm. 331
>Stanford Stable Isotope Laboratory - Green Earth Sciences Rm. 332 & 334.
>e-mail: [log in to unmask]
>WWW: http://pangea.stanford.edu/isotope/dam
>****************************************************************************
>
----------------------------------------------------------
William J. Showers
Dept. of Marine, Earth, & Atm Sciences
1125 Jordan Hall
North Carolina State University
Raleigh, NC  27695

(919) 515-7143 - voice
(919) 915-1498 - cell
(919) 515-7802 - fax
[log in to unmask] - office email

Even if you are on the right track, you'll get run over if you just
sit there.