Dear Isogeochemers,

I've been watching with interest the comments on quartz liners, and I must
say having used them for almost 3 years now, I can't imagine trying to
vacuum out my system. I too have a Geo 20/20 and get our glass blower to
make them up to fit the combusiton tubes. I place a small plug of quartz
wool in the base (so material doesn't fall out), and they are slotted
around 2/3 of the way up with a small hole pierced at the top so a piece of
bent coat-hanger wire can hook them out of the combustion tube and they are
then hung up to cool. I have several which I am rotating at any one time.

Each lasts over 10-20 uses, and I change the liner every 1-2 days depending
on the type and size sample I am doing....Normally after every 120-170
samples, although if I am doing nitrates or samples with sulphur or
inorganic contaminants (in C:N mode) I'll change it straight after as I
feel this can sometimes slightly affect the chemicals in the combustion
tube...probably not true, but call me paranoid! I have found no drift or
linearity problems using the liners and have heard too many horror stories
on ash clouds and toxicity, not to mention continuous breaking of quartz
combusiton tubes by accident, to want to try vacuuming.

I don't have problems with glass filter papers glueing up the liners
either. However once the quartz liners are a little older and becoming more
fragile, they are harder to get the glass filter papers out and tend to
break more easily. The liners can break off part way up, but they are still
usable until most of the slotted part is broken off. Generally if analysing
material on glass filter papers I'll tend to use quartz liners that are
fairly new (and hence less fragile) to avoid this problem.

Regarding the C:N isotope effects of low samples...yes I too see negative N
isotope numbers usually for sample which contain very low nitrogen and more
negative carbon isotopes when the carbon content starts to get really low
as well (usually below 0.1% or 0.05%). I will try scrubbing out the CO2
peak next time I'm working with low nitrate contents as previously suggested.

Cheers

Karyne
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Dr Karyne Rogers
Stable Isotope Laboratory Team Leader
Institute of Geological and Nuclear Sciences
PO Box 31-312
Lower Hutt
New Zealand

tel +644-5704636
fax +644-5704657
email [log in to unmask]
Web Site: http://www.gns.cri.nz
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