For what it's worth.... Our CE NA1500 Series 2 (EA) running on a Delta plus
is now setup using the oxygen as the purge. Originally when we were using
the AS200 carousel on the EA the helium was used as the purge as per the
original instrument configuration. The flow rate through the fixed
constrictor on the purge using helium was 25 ml/min. Plenty of flow to
purge the small volume of the AS200 carousel.

We are now using the AS128 carousel on the EA. The helium flow rate on the
fixed constrictor (25ml/min) was not enough to purge the larger volume
carousel. We had two options, by-pass the constrictor using a metering
valve or use the oxygen as the purge. After running some tests, I found
that using the oxygen as a purge would not consume any additional gas.
Baselines and blanks are excellent.

Original configuration using AS200:
He flow rate 60-65ml/min at 100kPa
Oven temp 60 deg C
Oxygen flow 30 - 40 ml/min @ 100kPa, 10ml sample loop
Helium purge = 25ml/min
4 meter column

Present configuration using AS128:
He flow rate 60-65ml/min at 100kPa
Oven temp 60 deg C
Oxygen flow 30 - 40 ml/min @ 100kPa, 10ml sample loop
Oxygen purge = 25-30ml/min
4 meter column

I should note that the flow rates and temps I am using are setup so we can
do a slow peak jump between the nitrogen and carbon analyses. Slow peak
jump means we do a peak center on C during the jump. Time between N and C
is approx 88 seconds. The slow peak jump takes approx 50 sec.

Dave

At 09:43 AM 5/24/99 +0200, you wrote:
>Isogeochemist and especially Dr William J. Showers of North Carolina State
>University
>
>
>on our CEInstruments Elemental analyzer we used Helium and Oxygen as
>utilities.
>
>In the EA1108 the Oxygen is used for  Flash Combustion while Helium is used
>as carrier gas and purge gas.
>The function of purge is to eliminate the presence of air , therefore N,
>over the tin container before dropping in the oxidation reactor.
>
>In the CE 2500, Helium is carrier gas while Oxygen has double function :
>oxidative gas and purge gas.
>Using Oxygen as Purge gas, the blank value is reduced (10 time less): this
>factor was very important for  trace elemental analysis
>Consequently in CE2500 configuration, also the He consume , using only for
>carrier , is riduced.
>
>According to the autosampler used the Oxygen flows for purge in CE 2500
>are the following:
>
>AS200  40 - 50 ml/min
>AS128   80 ml/min
>
>while for EA1108, the Oxygen use for Oxidation gas  was 10 - 20 ml/min :
>this is the reason of the different Oxygen  gas consume in EA1108 and CE2500.
>
>Best regards
>
>
>
>Guido Giazzi
>Product Manager
>CE Instruments - Rodano Italy
>phone   ++39 02 95059336
>fax     ++39 02 95059309
>
>
****************************************************************************
David A. Mucciarone
Laboratory Manager
Stanford University
Department of Geological and Environmental Sciences, 320
Stanford, CA 94305-2115
650-723-0817 (office) 650-725-0979 (fax)
Office - Green Earth Sciences Rm. 365
Stanford Stable Isotope Laboratory - Green Earth Sciences Rm. 332 & 334.
e-mail: [log in to unmask]
WWW: http://pangea.stanford.edu/isotope/dam
****************************************************************************