Dave, Why do you have to run your Oxygen line at 30-40 mL min-1 to purge a
10 mL loop? You don't give analysis time but with a 60 mL min-1 flow rate,
60 C oven and 4 meter column I am guessing that your analysis time is over
8 minutes. Wouldn't 10 ml min-1 of O2 for 8 minutes purge the O2 loop 8
times in 8 minutes and then use He to purge the samples? Would it be
possible to simply use a 10 mL min-1 O2 purge plus a 25 mL min-1 helium
purge, and tee them together into the sampler purge?
For that matter, does anyone out there know why CE instruments C/N
analyzers come with such a high O2 purge through the O2 injection loop?
At the same time I might ask as to why the ones I have seen from the
factory come with a 25 mL loop, which in our initial experience went
through copper columns every 200 samples? Why not ship them with 10 mL
loops?
Also, I am curious as to why it would be necessary to do a peak center on C
when jumping from N to C. My Europa Sci. 2020 manages to go days without
any retuning of the source and continually jumps back and forth between N
and C tuning. Is it really necessary on a delta plus to peak center on
every sample?
Paul.
At 06:53 PM 5/24/99 -0700, you wrote:
>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
>****************************************************************************
>
>
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