Hi Priscila,
I ran into the same problem a few years ago -- had a really old
scintillation counter but no information on efficiency and no
standards. If you use the old standards, I think there will always
be caveats to the measurement. For example, I don't think the
difference in scintillation liquid or vial type should be a problem,
but I don't know for sure. If it's really important, you might be
better off buying new standards.
When I asked our radiation safety office about this, they basically
told me that they don't bother calculating dpm and just go by cpm.
So my conclusion at the time was that what's good enough for the
radiation safety people is good enough for me, and I did all my
calculations with cpm. The dpm calculation is just for comparing data
between instruments, right?
Sorry I can't be of more help.
Good luck!
Irit
On Jul 8, 2010, at 5:16 AM, Priscila Peña Diaz wrote:
Hello All
I'm performing transport assays using 3H-labeled ATP and our
scintilation
counter is so old the manuals are lost and the standards used for
it are as
well. Nevertheless the thing works.
My question is regarding the calculation of dpms. As far as I know
the
efficiency of the apparatus to measure the isotope is what defines the
relationship between cpms and dpms. I managed to find some 3H
unquenched
standards from 1966. The date should not be a problem as the decay
can be
easily calculated. The problem is the scintillation liquid they
are in. I
have no idea what the cocktail might be, although its must be a mix of
toluene, which is what was used in the old days. We use a
biodegradable-scintillation liquid. If I use these standards in this
solution, can they be compared to the counts I obtain using the other
scintillation liquid? Should I purchase a standard in the same
liquid as I
use? Also the vials are different. The standards are in a
transparent vial
and we use plastic opaque vials for our measurements. Also an issue??
Suggestions appreciated...
thanks
Priscila
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