[ RadSafe ] LSC Method Assistance Needed - CO2

Tue Jan 12 14:27:10 CST 2010

Dear Enoch:

Indeed, the efficiency of single-pass bubbling through a medium is a
concern.  Here are a couple of anecdotal accounts based on my experience:

The opposite problem, air stripping a sample of water for radon, requires
about 1-2 minutes to reach equilibrium conditions in a closed circuit system
with the volume of air being roughly equal to the volume of water and the
total volume of air is bubbled 2-3 times through the water.  At least that
was my experience a few years ago.

Air-stripping can and has been used to efficiently strip radon from water
systems and approaches 99+% efficiency.  My modeling of radon release from
spray irrigation systems assumes that virtually all of the radon contained
in the groundwater is released, especially considering the very fine
droplets of water produced from the spray - providing a quite high surface
area.

Another experiment involves CO2 equilibrium in aqueous solutions:  I
required my students to measure the begin and end pH of distilled water and
CaCO3-dominated water using a bubbler through which air was bubbled.
Equilibrium took several minutes to achieve with a water volume of 250 ml
and a pre-rinsed fish tank bubbler system.  In the case of the distilled
water, the "endpoint" was reached when the pH dropped to 5.6 (equilibrium
conditions for atmospheric CO2) and 8.3 for CaCO3 dominated water.  These
endpoints were modeled using PHREEQC as well as measured rainwater pH and
analytical calculations.

So efficiency of a single pass for a bubbler would be hard to estimate,
unless the volume of gas sample was sufficient to cause the aqueous solution
to reach or approach equilibrium conditions.

Dan ii

--
Dan W McCarn, Geologist
2867 A Fuego Sagrado
Santa Fe, NM 87505
+1-505-310-3922 (Mobile - New Mexico)
HotGreenChile at gmail.com (Private email)

-----Original Message-----
From: Tung, Enoch [mailto:Enoch.Tung at PERKINELMER.COM] 
Sent: Friday, January 08, 2010 08:55
To: Dan W McCarn; Dale Boyce; radsafe at radlab.nl
Subject: RE: [ RadSafe ] LSC Method Assistance Needed - CO2

Thanks Dale and Dan.  I think you two were able to accurately gauge what
my ambiguous question was asking.
My question via Barb/Radsafe probably wasn't as clear as it should have
been.

The elixir that we use comprise of scintillation fluid and other
constituents, which adds up to the chemicals I/Barb listed.

I should have asked how other people capture CO2, and then what they
used to count the samples.

Considerations for it would include efficiency of the CO2 capture, and
type of scintillation fluid/chemicals used to minimize any collateral
effects (quench, chemiluminesce, etc) that the trapped CO2 solution
would have on the counting.

How efficient is 2NaOH + CO2 = > Na2CO3 reaction?  A chemist told me it
would be pretty efficient (assuming adequate flow rate/surface to area
ratio). Does the reaction occur immediately on contact between the
molecules?

Thanks,
Enoch Tung

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
Behalf Of Dan W McCarn
Sent: Friday, January 08, 2010 12:11 AM
To: 'Dale Boyce'; radsafe at radlab.nl; blreider at aol.com
Subject: RE: [ RadSafe ] LSC Method Assistance Needed - CO2

Dear Dale:

I was about to step into this discussions with exactly the points that
you
raised regarding the mineralization of CO2 to carbonate in a high pH
environment.  I'm glad that you explained the reason for maintaining a
high
pH environment in order to prevent loss of CO2.  This saves me from
running
my mineral-equilibria codes to demonstrate the reason!

Dan ii

--
Dan W McCarn, Geologist
2867 A Fuego Sagrado
Santa Fe, NM 87505
+1-505-310-3922 (Mobile - New Mexico)
HotGreenChile at gmail.com (Private email)
-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
Behalf
Of Dale Boyce
Sent: Thursday, January 07, 2010 21:16
To: radsafe at radlab.nl; blreider at aol.com
Subject: Re: [ RadSafe ] LSC Method Assistance Needed - CO2

One comment that I haven't seen addressed. The NaOH in the original
cocktail

will capture CO2 as carbonate. Solutions with pH on the basic side tend
to 
cause many, if not all cocktails to chemoluminesce.

If I were starting from scratch, I would look for cocktails with a high 
aqueous capacity, as you may need to wait awhile before counting (keep
the 
samples in the dark as well). Setting a lower level discriminator above
the 
chemoluminescence will help assuming you have control over this.

In developing the procedure, I would recommend counting individual
samples 
as a function of time. Prepare any standards from a C-14 carbonate
solution.

You don't want to calibrate with an organic C-14 standard, as the
organic 
will follow the organic phase during organic aqueous phase separation,
while

your C-14 of interest in your sample will follow the aqueous phase.

Do not acidify either your samples or standards at any point. You will
lose 
CO2, and not be able to rely on your results.

Make quench standards specific to your sample and cocktail formulation. 
Maybe a little overkill, but you are developing a new procedure for a 
technique that is on the edge of "normal" lsc usage. Also, look in the 
literature for C-14 carbon dating using LSC. It has been used, and there

should be some papers out there. Typically these were also CO2 samples.

Have fun, and possibly get a paper out of the effort!

Dale 

_______________________________________________
You are currently subscribed to the RadSafe mailing list

Before posting a message to RadSafe be sure to have read and understood
the
RadSafe rules. These can be found at:
http://radlab.nl/radsafe/radsaferules.html

For information on how to subscribe or unsubscribe and other settings
visit:
http://radlab.nl/radsafe/

_______________________________________________
You are currently subscribed to the RadSafe mailing list

Before posting a message to RadSafe be sure to have read and understood
the RadSafe rules. These can be found at:
http://radlab.nl/radsafe/radsaferules.html

For information on how to subscribe or unsubscribe and other settings
visit: http://radlab.nl/radsafe/