We are using the EA for C and N only. Paul.
At 11:30 AM 2/16/00 -0500, you wrote:
>Are you using your EA for C/N or S analysis?
>Stable Isotope Geochemistry wrote:
>> All EA users:
>> I thought this might interest you, I would appreciate any comments. Paul
>> >>>Hi Paul:
>> >>When you "vacum" out your EA, are you cooling it down or turning off
>> >>the ovens completely?
>> >>I was just wondering if it was better to remove ash with things warm
>> >>or completely off?
>> >We do not turn off the ovens, or even turn them down to standby. We have
>> about a 9.5mm outer diamter copper tube (3/8 of an inch OD) connected with
>> thick flexible tubing to an erlenmeyer flask. The tube happens to be
>> copper but that was simply what we had when we put it together. The flask
>> is connected to simple none high vacuum pump that has a high volume
>> throughput at about 70 cm mercury vacuum. This pump has micron sized
>> filters on both the inlet and outlet. The erlenmeyer flask has a glass
>> tube that goes through a stopper to a few cm from the bottom of the flask,
>> and at the top near the outlet we stuff some glass wool to help stop dust
>> going out of the outlet.
>> >With 9x5mm tin capsules burning plant material we vacuum the ash every 200
>> samples or so, usually at the begining of a run in the morning. We simply
>> take the fitting off the combustion tube and insert the copper tube into
>> the ash, then twist and move it back and forth. This usually removes all
>> the ash from the prevous run. If necessary we have a long drill that we
>> can insert into the combustion tube to try and loosen ash. Both the copper
>> tube and the drill are marked so that we don't dig down into the chromium
>> oxide. We don't leave the copper tube sucking in the combustion tube for
>> more than 10 seconds at a time.
>> >For soils we vacuum out the ash immediately (or first thing the next
>> morning) after every run of about 60 samples. Otherwise we find that the
>> ash becomes so hard we cannot loosen it.
>> >This procedure keeps a combustion tube in good working condition for at
>> least 2000 samples. We usually replace the tube after this as then the
>> cost per samples is only on the order of US$0.20 each for the combustion
>> tube, and it is not worth the possability of any trouble to save only a few
>> cents per sample by trying to make the tube last longer.
>> >When it is being vacuumed the temperature of the combustion tube falls and
>> it is not red hot anymore, but using the white opaque combustion tubes this
>> doesn't seem to damage the tube.
>> >We have tried liners to remove the ash but have found them more expensive
>> and difficult to use than vacuuming the ash out.
>> >Be carfeul to ensure that your vacuum line has good filers on it. The
>> Chromium oxide is bery toxic and its dust must not be allowed into the
>> >Hope this helps,
>> >Paul Brooks.
>> >At 06:51 AM 2/15/00 -0800, you wrote:
>> Paul D. Brooks.
>> Dept. ESPM-Ecosystem Sci.,
>> 151 Hilgard Hall, MC 3110,
>> UC Berkeley, Ca. 94720-3110.
>> phone (510)642-3155
>> FAX (510)643-5098 (to Att. Paul Brooks)
>Gregory A. Wandless
>US Geological Survey
>Reston, VA 20192
>Email:[log in to unmask]
>Phone: (703) 648-6189
Paul D. Brooks.
Dept. ESPM-Ecosystem Sci.,
151 Hilgard Hall, MC 3110,
UC Berkeley, Ca. 94720-3110.
FAX (510)643-5098 (to Att. Paul Brooks)