Hi Yanhua

We use thin wall alumina tube liners in preference to glass, in a Fison/Thermofinnigan 1500 CHN EA.

To use them, we pack the bottom end with a small plug of quartz wool (not too tight) about 1 cm long and then put a layer 1cm of chromium dioxide granules on top.  We load the liner into the combustion tube by lifting off the  sample carousel and lowering the liner into the combustion tube with a stiff bent wire. With the wire at a small angle it will hold the liner  OK. This can be done with the combustion tube at 1020oC . When the sample carousel is refitted, it takes about 15 minutes to stabilise again. Removing or replacing the liner is the reverse and takes less than 10 minutes so there is no need to lower the combustion furnace temperature.

In practice, we change the liner each morning and occasionally during the day if glass fibre filters are being used.  The wad of ash in the used liner is pushed out with a metal rod when it has cooled a bit. A small bit of the liner may break off at this time but the liner is still re-usable until it gets too short to last the whole day.  

For glass liners, I would suggest putting the slots at the bottom and the open end at the top and pack the liner much the same as we do.

We get the alumina liners from:
Du Bray & Associates
Overseas Procurement Specialists
PO Box 4537, Auckland
ph. 09 358 0326
fax 09 358 0471
email [log in to unmask] 
www.dubray.com 

For a Delta+, we order:
Degussit AL-23 alumina tube, open both ends, thin walled, OD 12mm, ID 11mm, length 400mm.

Once they arrive we send them off to the glassblower to get them cut to  length to fit in the combustion tube (each tube into 3 pieces).  

You would need to check the dimensions against your EA combustion tube if you want to use these.

Cheers

Max




Max Gibbs
NIWA, PO Box 11-115
Gate 10 Silverdale Rd
Hamilton 3251
New Zealand
 
Phone: +64 7856 1773
Fax: +64 7856 0151
Cell: 027 604 1449
Email: [log in to unmask]
>>> Yanhua Feng <[log in to unmask]> 19/11/2009 11:58 a.m. >>>
Dear all,
   We have a EuroVector EA 3000 for CN analysis. I am always concerned 
about incomplete combustion after some ash piled in the combustion tube. 
especially with acid fumigation samples, I use two silver capsules for each 
sample. 
  I heard that there is a way to remove the ash with an insert tube. I am 
wondering if anyone has experience on that. We have a few tubes in the lab. I 
think that they are insert tubes. 22cm long, transparent glass, thin wall, 4 
slots on one end. But there is nothing to tell me how to use them. the end 
with slots should be on the top or the bottom. etc. 
   I could also buy some new ones if someone can tell me which kind fit my 
instrument. etc. 
   appreciate any suggestion. 

Yanhua Feng
New Mexico State University
Plant & Environmental Sciences
Las Cruces, NM 88003

NIWA is the trading name of the National Institute of Water & Atmospheric Research Ltd.