RE: Analytical method

["Pombier, Edward C." <epombier@med.miami.edu>]

Radsafers:

As some of you may remember, I was interviewed on a local TV show here in
Miami regarding meetings held here by the Tooth Fairy Project people.  This
list was very useful in providing me with information for that interview.
Below is one of the documents which was provided to me on the condition that
the source not be identified.  It is in the first person and I am not the
one who generated the information.  Hope it provides some information for
those of you in the analytical world.

"An investigation was performed to determine the protocol used by the
laboratory performing the analysis for Sr-90 in teeth for the "Tooth Fairy
Project". 
We were informed that the facility doing the analysis was the University of
Waterloo's Environmental Isotopic Laboratory (EIL).  On August 31, 1999, I
contacted Mr. Robert Drimmie, director of the EIL (telephone number
519-888-4567), and introduced myself as a Scientist hoping to discuss their
analysis procedure.  Mr. Drimmie quickly pointed out that his laboratory
does not perform this type of analysis.  He directed me to the person doing
such work, Dr. Sharma, a former scientist in his lab.  He told me that Dr.
Sharma works for a company called REMS.  I was able to get Dr. Sharma's
telephone number from him (519-885-2520).
I then called Dr. Sharma this same day and introduced myself.  Requesting
information on his analytical technique he was very willing to discuss his
procedure.  Following is a summary of his procedure:
He typically analyzes one tooth at a time, sample weight approximately 100mg
(0.1 gram).  He claims that 24% of the weight is attributed to calcium and
reports his results in pCi/gram Ca.  
He dries the sample at 110°C, grinds it, and dissolves it in acid.  The acid
is then evaporated to dryness.  The residual is redissolved and then a
calcium carbonate precipitation is performed.  The precipitant is
centrifuged and separated into a liquid scintillation vial.  He then counts
the sample via scintillation counting.
The liquid scintillation counter he uses is a Quantalus Model LKB 1220X.  He
sets his windows at 400 to 1000 channels (200 to 500 keV).  He said below
400 would give tritium and C-14 interference.  The efficiency he uses is
based on a Sr-90 source he received from NIST.  He noted that the Sr-90
source is certified by NIST with a known dpm activity, and since the Y-90 is
in equilibrium with the Sr-90 he uses a counter efficiency of 1.8 in order
to account for both Sr and Y.  The backgrounds he normally sees is 2.3 cpm,
with a count time of 400 minutes per sample.  With this protocol he claims
that his sensitivity (MDA) is less then 1.0 pCi/g Ca.  He's currently
analyzing 20 teeth/week.  The results he has seen so far are between 0 and
10 pCi/g Ca.  He did note that very few are at the upper range but most of
them are between 0 and 1 pCi/g Ca.
He told me that he does not know the location from where the teeth come
(blind study) and that he is working for a "charitable organization".  

On September 1, 1999, I called Dr. Sharma again with some follow-up
questions.  Again, he was very cordial and open to discussing his procedure.
He also told me that he's in his 70's and semi-retired.  He was hired as a
consultant for REMS Inc. (Radiological Environmental Monitoring
Specialists).
I wanted to find out more about his counter so I asked him again about the
window setting that he uses, i.e., 400 to 1000 channels.  He did not know
what the channel per keV was, but he said that while in the logarithmic
scale he gets two distinct peaks, one for strontium at approximately channel
500 and another for yttrium between channels 600-700.  When he sets his
window from 0 to 1000 channels his background increases to 3.4 cpm.  By
using 400 to 1000 channel window his background drops to 2.3 cpm, thus
giving him a lower sensitivity. 
As stated earlier, he forms a calcium carbonate precipitation.  He then
repeats this process by washing with weaker dilutions of sodium carbonate
until he gets a white calcium precipitant.  This is dissolved in pH of 2
then diluted up to 2.0 ml with 2N acid.  He removes 0.1 ml for Atomic
Absorption analysis to determine the the calcium content (between 24 and
27%) and also to determine chemical yield of the analysis from strontium
nitrate carrier.  The remaining 1.9 ml is mixed with 11.9 ml Ultima Gold AB
(he said he was not certain of the Ultima Gold volume).   He claims that he
eliminates all interferences (such as, K-40) because of the many calcium
carbonate precipitations performed.
He does not participate in any cross-check program, but he said he would
like too.  He asked me with whom we participate  and asked if I could send
him information so he can get into a program.  He also asked me something
very interesting.  He asked if I would be interested in doing split samples
with him.  He gets a number of molars that he cuts in half for his analysis.
He would be very eager to send the other half to me for an interlaboratory
comparison.  I informed him that I would discuss this matter with my manager
and get back to him in the near future.  "




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