RE: Measurement of Tritium by Liquid Scintillation

[Franz Schoenhofer <schoenho@via.at>]

At 08:02 04.05.98 -0500, you wrote:
>Radsafers:
>
>A significant problem with measuring tritium in urine is quench.  
>What I do is run replicate samples by liquid scintillation 10 ul, 
>50 ul, 100 ul, and 1 ml of urine in 7 ml of scintillation fluid.  If 
>they all read background, I stop there.  If the readings are linear, 
>then quench is not a significant factor.  If the readings are 
>nonlinear, I either take the most conservative value or spike a sample 
>with a known activity of tritium or both.
>
>Running several samples of varying concentration is a quick and easy 
>way to evaluate whether quench is significantly affecting sample 
>counting.
>
>Tom
>Tom Mohaupt, MS, CHP
>Wright State University
>Radiation Safety Officer
>
>Voice:  (937) 775-2169
>Fax:  (937) 775-3301
>E-mail:  tmohaupt@wright.edu
>Address:  104 Health Sciences Bldg, Wright State University
>          Dayton, OH 45435
>
>------------------------------------------------

We had urin samples which were so heavily quenched, that the efficiency was
0.3 %. 

We therefore take 1 ml of urine, dilute it with 7 ml of water and then add
12 ml of a gelforming cocktail. The dilution results in a much lower quench
and we have efficiencies of at least 15 % for tritium compared to appr. 25%
for tritium in distilled water. This is good enough even for relatively low
concentrations of tritium. We "eliminate" the problem of quench by using
tritium as an internal standard, so we have the exact efficiency.

In my opinion it is wrong to distill the urine sample, because then
organically bound tritium will not be measured and therefore the result
will not be representative for the tritium content of the body. Furthermore
it is not a very pleasant job to distill urine, it takes time and costs money.

Franz


Franz Schoenhofer
Federal Institute for Food Control and Research
Department for Radiochemistry and Radioactivity of Food
Kinderspitalg. 15
A-1095 Vienna
AUSTRIA
tel.: +43-1-40491-520
fax.: +43-1-40491-540