Dear Blair,

On 20 April you wrote:
>
> I'm currently looking at resource utilization of a desert bird community
> and measuring the delta 13C of the breath from small birds in the field.
> I am collecting  samples in LABCO exetainers; these 12ml pre-evacuated
> vials are sold by PDZ Europa.  The CO2 levels of my samples range from
> 350 to 10000ppm and from -13 to -25 per mil VPDB.  These vials cost
> about $34.00 per 100.  I am looking for vials with similar
> characteristics.

$34 for 100??? This is daylight robbery. If you are really paying
this princely sum, I'm afraid to say you'r being ripped off.

> I was wondering: 1) what types of containers, of this general type,
> others have used for gas sampling and the manufacturer's contact info,
> and 2) has anyone tested the archival qualities of these particular
> vials or others; do they leak, are there diffusional problems with the
> septa for CO2, how long can samples be stored in these containers
> without undergoing significant fractionation or loss of sample gases,
> how do they do with repeated use etc...

For breath test with human subjects I'm using 'exetainers' as
supplied by Isochem (for address see below). These exetainers are 12
ml, pre-evacuated (sigh!) screw top containers with green plastic
caps containing a septum. Isochem are asking GBP138 for 1,000
(discount for larger quantities) and GBP39 for 1,000 replacement
caps-cum-septa. You see, unless you actually break a container the
only thing that wants replacing is the septum.

Allegedly, you can store human breath samples for up to 3 months in
these containers but I tend to measure mine within a fortnight (at
the latest) of sampling.

Since it poses no problem to displace the ambient air in the
containers quantitatively with breath by breathing down the container
with the aid of a straw, I am not too worried about the composition
and 13C signature of whatever happens to be in the container prior to
sampling. With birds that might be a different matter entirely. By the
by, how do sample bird breath anyway? With difficulty and great
skill, no doubt. But seriously, how do you do it?

If you require evacuated containers you are better off doing the
evacuation yourself as shortly as possible before sampling. I find
that almost every other container out of a box of 200 has lost its
vacuum by the time of delivery/usage; and the degree of vacuum for
the remainder varies a great deal.

If you are not worried about the vacuum but about 13C signature of
the background CO2, it might be a good idea to flush your containers
with N2 (do NOT use Ar!!!).

Oh yes, and another thing, don't tighten the caps beyond finger tight
(septum centre bulging out towards the tube). Tightening them too
hard increases the chance of a leak.

Of course, the are the vacutainers (originally designed for blood
sampling) that look like test tubes and are sealed with a thick red
rubber stopper. In my experience, their advantage (big red rubber
stopper) turns out to be their greatest disadvantage: it's a needle
killer.First, replacing the needle of the Gilson autosampler is a
bit awkward and expensive, too. Secondly, if one relies on the vacuum
(which one shouldn't; even these stoppers don't prevent loosing the
vacuum over time) to draw one's sample in, pushing a syringe needle
through the stopper is not a thing one wants to do in a hurry, and it
invariably leads to material abrasion. One always finds rubber
particles in the tubes and, more annoyingly, in the needle (even in
the side vented ones).

Finally, the UK address for Isochem:

Isochem Ltd
1 Marino Way
Finchampstead
Wokingham
Berkshire       RG40 4RT
UK

Tel: +44-(0)118-9735557
Fax: +44-(0)118-9735092


Hope this helps.


Best wishes,
                       Wolfram


***************************
Dr. W. Meier-Augenstein, CChem MRSC
Senior Research Fellow

University of Dundee, Dept. of Anatomy & Physiology,
OMS, Small's Wynd, DUNDEE  DD1 4HN, United Kingdom

Tel.: +44-(0)1382-34/5124, /4574, /4968
Fax:  +44-(0)1382-34/5514

e-mail: [log in to unmask]

URL: http://www.dundee.ac.uk/anatphys/wma/wolfram.htm


NB Message is confidential and for recipient only: Unauthorized reading and copying
may result in legal action! Opinions expressed those of author not institution.
LEGAL NOTICE: Unless expressly stated otherwise, this message is confidential and
may be privileged.  It is intended for the addressee(s) only.  Access to this
e-mail by anyone else is unauthorized.  If you are not an addressee, any
disclosure or copying of the contents of this e-mail or any action taken (or not
taken) in reliance on it is unauthorized and may be unlawful. If you are not an
addressee, please inform the sender immediately.