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 >**************************************************************************** > >