Why won my polyacrylamide gel polymerize?
Poor or slow polymerization of acrylamide is most likely the result of an older solution of ammonium persulfate (APS) solution which has gone off. First try making a fresh stock from solid material. Netters have several quick tests to see if the APS is still good. One way is to put some in a test tube and add the correct volume of water to make 10 mg/ml. If you hear it snap, crackle, and pop, then it is still good. This is because some gas forms within the crystals when water is added to APS which causes them to pop. Another way is to prepare solution of NaI in water and add your APS to it. If the color changes to brown, the APS is still good. Opinions vary concerning how long APS is stable. Some netters store a 10% stock of APS at 4 degrees C for several weeks, while others make 10% APS and freeze single use aliquots at -20. Still others make just enough fresh solution for a single gel just before pouring one. If all tests for polymerization fail, the next thing to test is the solutio
