We always visually judged the correct temperature for LN2 cooled isopentane, by using a glass beaker, although as long as you use a container to see the following described appearance of isopentane aka 2 methylbutane when cooled, it will work.
We lowered a glass beaker (containing isopentane) hanging from a wire holder (redesigned coat hanger!) into a Dewar of liquid nitrogen. When the isopentane becomes thick e.g. viscous, like Karo syrup or molasses, and the bottom of container had isopentane looking a bit white, the temperature was reached ~minus 120C. If we tried to test the temperature with a RT warm thermometer designed for cold temperatures, the isopentane immediately becames less viscous, and the temperature skewed towards warm. Doing this visually was much better than using a thermometer. In fact, if one cools isopentane to the point of becoming a solid aka a glass or super-cooled liquid, you can stir the isopentane with a long, RT metal forceps to let solvent go back to liquid and start over. As for isopentane, storage in an explosion proof refrigerator or freezer is mandatory, or store at room temperature if room is not too hot, in a flammable storage cabinet. This is what we have done in the past. It pays to be safe, and also use a fume hood to not breathe fumes from this solvent. Gayle Callis HTL/HT/MT(ASCP) Bozeman MT -----Original Message----- From: histonet-boun...@lists.utsouthwestern.edu [mailto:histonet-boun...@lists.utsouthwestern.edu] On Behalf Of Robert Richmond Sent: Thursday, November 19, 2009 11:22 AM To: histonet@lists.utsouthwestern.edu Subject: [Histonet] Re: freezing skeletal muscle Galina Deyneko asks about freezing skeletal muscle. I'm not sure that temperature control of the isopentane is too important - it should be very slightly viscous. But do get rid of explosive isopentane and get a non-flammable substitute - see my previous posts on this topic. The technique for freezing skeletal muscle is easier demonstrated than described. Hold a small piece (maybe 5 x 10 mm) in tweezers, and coat it with talc powder so that it appears white on the surface. Then dip the specimen in and out of the isopentane - roughly two dips per second - until it is frozen solid. That will eliminate the ice crystal artifact. But you have to try it a few times before it will quite work for you. Set aside one dead rat and one afternoon. Bob Richmond Samurai Pathologist Knoxville TN _______________________________________________ Histonet mailing list Histonet@lists.utsouthwestern.edu http://lists.utsouthwestern.edu/mailman/listinfo/histonet __________ Information from ESET Smart Security, version of virus signature database 4623 (20091119) __________ The message was checked by ESET Smart Security. http://www.eset.com __________ Information from ESET Smart Security, version of virus signature database 4623 (20091119) __________ The message was checked by ESET Smart Security. http://www.eset.com __________ Information from ESET Smart Security, version of virus signature database 4623 (20091119) __________ The message was checked by ESET Smart Security. http://www.eset.com __________ Information from ESET Smart Security, version of virus signature database 4623 (20091119) __________ The message was checked by ESET Smart Security. http://www.eset.com _______________________________________________ Histonet mailing list Histonet@lists.utsouthwestern.edu http://lists.utsouthwestern.edu/mailman/listinfo/histonet