[ RadSafe ] Scintillation Counting Question

Fri Aug 29 08:21:56 CDT 2008

May I suggest some excellant references on this subject. Horrocks and
Kobiashi have written extensively on sample preparation for liquid
scintillation counting. Also, Beckman has produced several works on
this topic.

Thomas Johnston
Health Physicist

On Fri, Aug 29, 2008 at 8:31 AM, jock thomson <jthoms at yahoo.com> wrote:
> I have encountered this type of problem many times. The solution is relatively strightforward.
> The problem is simply one of limited solubility. The count rate increases as the small volume sample slowly dissolves. Extended shaking or ultrasonic treatment will not work.
> To resolve this problem simply add about 500 microlitres of either water or another low quenching solvent that the sample compound is known to be soluble in. Ideally you should add this 500 microlitres to the sample prior to adding the cocktail and that way you will not encounter variable count rates.
> Be aware that certain electronegative solvents such as halogenated solvents are very quenching. I would normally suggest adding either water, ethanol, acetonitrile, ethyl acetate or hexane as these are all low quenching.
> Hope this helps resolve the problem.
> Regards
> James Thomson
> Meridian Biotechnologies Ltd.
> Unit 12 Pottery Lane West
> Chesterfield
> Derbyshire S41 9BN
> England
> Tel: (+44)-1246-559834
> Cell: (+44)-7989-688143
>
>
>
>
> ----- Original Message ----
> From: "Nielsen, Erik" <nielseec at nv.doe.gov>
> To: radsafe at radlab.nl
> Sent: Wednesday, August 27, 2008 11:18:57 AM
> Subject: [ RadSafe ] Scintillation Counting Question
>
>
> To expand on Cary's comment.
>
> I would recommend vigorous shaking of your sample/cocktail mixture and
> degassing it by setting it in an ultrasonic cleaning bath for a few
> minutes.  The ultrasound will degas the sample as well as contribute to
> the homogenization of the sample/cocktail mixture.
>
> Erik C. Nielsen
> Senior Scientist
> Remote Sensing Laboratory
> P.O. Box 98521, M/S RSL-47
> Las Vegas, NV 89193-8521
>
> http://www.nv.doe.gov/nationalsecurity/homelandsecurity/frmac/default.ht
> m
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>
> Message: 8
> Date: Tue, 26 Aug 2008 17:41:38 -0700
> From: "Cary Renquist" <cary.renquist at ezag.com>
> Subject: RE: [ RadSafe ]
> To: "Marshall, Elaine" <emarshall at lrri.org>,    <radsafe at radlab.nl>
>
> Just a thought...
> Perhaps it is a physical phenomenon.
> Since the tritium compound is moderately soluble, perhaps it initially
> forms
> small (microscopic) globules in the aqueous solution that eventually
> "dissolve"
> in the cocktail -- the globules might not be large enough to see, but
> large enough
> to keep the tritium beta from interacting with the cocktail.
>
> Cary
>
> -----Original Message-----
> From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
> Behalf Of Marshall, Elaine
> Sent: Monday, 25 August, 2008 14:47
> To: radsafe at radlab.nl
> Subject: [ RadSafe ] Scintillation Counting Question
>
> I have a researcher who posed the following question to me.  I have not
> experienced this yet and was wondering if anyone else might have an
> idea.
>
> "For this study counting tritium (as estradiol), we are using Ultima
> Gold cocktail, 10-12 ml for 40 microliter samples.  We are seeing
> something that seems odd to me:  after holding for at least half an hour
> in the dark, we get counts that seem low, and if re-counted a day or so
> later, the counts go UP, by about 50%, and reach the expected levels.  I
> know of a number of reasons for counts to go DOWN, but don't understand
> how they can go up.  We do make a point of mixing well, without shaking
> so much as to cause bubbles.  Any clue???"
>
> The researcher wanted me to add that these are aqueous samples, although
> the actual tritiated compound is only moderately aqueous-soluble.
>
> Thanks!!
>
> Elaine T. Marshall, CHP
> Radiation Safety Officer
> Lovelace Respiratory Research Institute
> 2425 Ridgecrest Drive SE
> Albuquerque, NM  87108
> (505) 348-9578
> emarshall at lrri.org
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