[ RadSafe ] LSC Method Assistance Needed - CO2

Dale Boyce daleboyce at charter.net
Thu Jan 7 22:16:13 CST 2010

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!


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