Hello All,
We at LSIS also have an airlock system based on
designs provided by John Valley/Mike
Spicuzza. We built the airlock to allow for analysis of clays on
our laser line. During my MSc. work, we found that it is possible
to measure reproducible values for our in-house clay mineral standard to
within +-0.3 permil (d18O) when pre-treated at 150 degrees C for 3 hours in
an evacuated chamber prior loading into the airlock. For clay
samples, we do not pre-treat with BrF5 as they may react at room
temperature. I found that each sample must have a specific procedure
developed to minimize splattering. In future we plan to try wrapping each
sample in foil and then loading them in each sample cup to further reduce
splatter. Have others tried this?
Sincerely,
Sam Russell
Laboratory for Stable Isotope Science
The University of Western Ontario
----- Original Message -----
Sent: Monday, May 22, 2006 8:15 PM
Subject: Re: [ISOGEOCHEM] laser ablation
for sulfate O
Hi Doug
>I am curious as to the number (if any) of folks
who have tried to do laser
>ablation with BrF5 for
>oxygen
isotope analysis of sulfate minerals as well as hydroxylated
>sulfur/sulfate species. I would
>like to analyze alunite,
and would like to hear from anyone who has gone down
>this road.
This is one of the first
minerals I tried to analyse when I was introduced to laser ablation. Little
did I know that it was a bridge too far. I'll summarise my experience
briefly, and if you want to discuss details we can do it "off-line". The
first thing I realised that it is was very difficult to get good or even
reasonably good replication of values. The problem is related to yield
which is related to the sample presentation (powder, single grains). I
had to work with powders and as you may know, dealing with powders and
lasering is a problem because the sample tends to fly about and/or splatter. I
had a 2 mm press for making little briquettes, but it didn't completely
resolve the problem. I tried all different ways of lasering (defocussed beam,
etc.), but never got any satisfactory results because it was impossible to get
100% everytime. Someone in Germany contacted me a few years ago and was
thin! king about doing a PhD using the laser method for analysing alunite, but
apparently gave up and ended using high temp combustion (~1000 degC), GC+MS.
I think this is the best way to go.
>Also, I
>am pondering the wisdom of doing clay minerals by
laser with BrF5, and recall
>several
>conversations with others
who were attempting this. We have an airlock design
>similar to
John
>Valley's/Mike Spicuzza's in Madison, but I would like to know if
the spattering
>issues during
>heating have been
solved.
I regularly analyse clay
minerals using the laser with good results. I dont have an airlock
system, so prior to putting the samples (loaded onto sample holder) into the
chamber, I leave them in a oven at 220 deg overnight and with some BrF5
pretreatment, most of the interlamellar water is removed. I have had
problems in the past with smectites, but suspect that they had poor
crystallinity which resulted in them reacting with BrF5 at RT. However, if you
have an airlock system, it shouldnt be a problem. You just need to
practise a little to get the right lasering technique and increasing the laser
power at a suitable rate to minimise splatter.
Sincerely
Kevin
******************************************************************************
Dr
Kevin Faure
Ocean Exploration
GNS Science
30 Gracefield Rd /
PO Box 31 312
Lower Hutt
6009
New
Zealand
http://www.gns.cri.nz/
Tel: +64-4-570 4638
Fax:
+64-4-570 4657