I have these plasmids with kanamycin resistance. I was able to transform them some time back. Now I am trying to transform again and its just not working. I used ampicilin plasmid as control just to know if my technique is correct and it works fine. Is there anything special about kanamycin? I am using 25ug/ml conc co selection(Which is less than most references but that's what is recommended by provider) I have checked the plasmids from original vial on gel and they look fine.