Technical Services p00475 at psilink.com
Fri Jan 20 10:47:49 EST 1995

>DATE:   18 Jan 1995 10:25:27 -0800
>Everyone using S35 labelled nucleotides needs to understand the
>following safety issue. When they irradiate to create the S35 labelled
>target molecule, they also make other S35 labelled species, some of
>which are volatile acids. When you open the vial, a cloud of S35
>labelled vapor comes out and will be trapped on basic or buffered
>surfaces (like inside your lungs).  The same thing happens when you
>heat a solution containing the S35 labelled nucleotides.  If you don't
>believe it, put an open container of S35 in a closed space with a
>scintillation vial containing some basic substance to act as a trap;
>then count it.  
>You need to handle this stuff in a chemical hood, especially when you
>open the stock vial or heat reactions in open tubes.  When you have
>tubes with S35 out of the hood, keep them sealed or on ice as much as
>possible.  You can do PCR safely with it; just avoid the variety that
>makes you open the heated tubes.  Also keep in mind that if you put
>open tubes in an incubator, you're going to get a labelled condensate
>on the cooler surfaces of the incubator (usually the door).  Then it
>gets all over your gloves, etc without you seeing it.  Then it gets
>spread everywhere and all your students say "It's not us, it's some
>phantom that sneaks into the lab in the middle of the night and tracks
>S35 around."
>Steve Hardies, Assoc. Prof. of Biochem., Univ. of Texas HSC at San
>Hardies at uthscsa.edu

We would like to second Dr. Hardies' observations on the necessity of
careful monitoring when working with S-35 labelled compounds.

One point requires clarification.  S-35 compounds are not prepared by
direct irradiation: only S-35 sulphate is prepared in this way.  The
sulphate is then used in the synthesis of the labelled compound.  This
is important because potentially volatile impurities are not present
when the compounds are prepared but grow in with time through the
processes of chemical and radiolytic decomposition.

The fact that impurities increase with time suggests a few ways to
prevent contamination:  First, use fresh S-35  labelled compounds, so
that the time for the growth of impurities is minimized.  Second, use
stabilized formulations of labelled compounds.  Various stabilizers
(such as pyridine 3,4-dicarboxylic acid, which is used with methionine
and cysteine) are effective at minimizing radiolytic decompostion of
stock solutions. Third, monitor work surfaces, incubators and
temperature blocks scrupulously.  Finally, consider the  use of other
isotopes such as P-33 where experimental requirements permit.

Peter Riis
Technical Services
Amersham Life Science Inc.
p00475 at psilink.com

More information about the Methods mailing list